Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts


EVOLUTION, Issue 5 2004
Samuel Cotton
Abstract We used the stalk-eyed fly Cyrtodiopsis dalmanni to examine predictions made by condition-dependent handicap models of sexual selection. Condition was experimentally varied by manipulation of larval food availability. Cyrtodiopsis dalmanni is a highly dimorphic species exhibiting strong sexual selection, and the male sexual ornament (exaggerated eyespan) showed strong condition-dependent expression relative to the homologous trait in females and nonsexual traits. Male eyespan also showed a great increase in standardized variance under stress, unlike nonsexual traits. The inflated variance of the male ornament was primarily attributable to condition-dependent (but body-size-independent) increase in variance. Thus, evaluation of male eyespan allows females to gain additional information about male condition over and above that given by body size. These findings accord well with condition-dependent handicap models of sexual selection. [source]


INSECT SCIENCE, Issue 4 2003
Ke Zhang
Abstract In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along the railway from Beijing to Guangzhou. Bioassay data showed that the resistance levels of the four populations to dichlorvos were high and to parathion moderate as compared with the susceptible strain and there was no significant difference among the four populations to the same organophosphate (OP) insecticide. Starch electrophoresis was done to identify the frequency of known overproduced esterases and to analyze genetic diversity among various populations by electrophoretic polymorphism of five presumably neutral loci. The results indicated that the gene flow between populations existed and the number of effective migrants (Nm) was related to collection geography (Nm from 1.67 to 40.07). In contrast with lower genetic differentiation between two nearby populations (between GZ and ZS, ZZ and SQ) and higher genetic differentiation between two distant populations (between GZ and ZZ), there was a significant and inconsistent difference in the distribution of resistance alleles, A2-B2 when explained only with active migration. This divergent situation could be straightened out when considering passive migration (such as railway transport) which increased the spread of A2-B2 along the railway, i.e., in GZ and ZZ. The resistance alleles, A2-B2, dispersing to around areas by active migration suffered from the limitation of gene flow and the speed of invasion. [source]


INSECT SCIENCE, Issue 3 2001

Abstract A new species of Culicoides, C. tahemanensis sp. nov. is described from Xingjiang Uygur Aut. Reg. in China. The new species is closely allied to Culicoides grisescens Edwards, but both of them are distinctly different in pale spots of cell R5 and cell A of wing of female, and shape of distal portion of aedeagus of male. The ninth tergum of new species is somewhat allied to C. nipponensis Tokunaga, but distinctly different in pale spots of cell R5, cell M2 and cell A of wing, and shape of aedeagus of male. The type speciemens are deposited in the Institute of Military Medical Sciences, Shenyang Military District, Shengyang 110034, China. [source]


INSECT SCIENCE, Issue 3 2001
CUI Yong-sheng
Abstract Two new species of the genus Coenosia Meigen from Mt. Fanjing of Guizhou Province, China, namely C. brevimana and C. fanjingensis, are described. The type specimens are kept in the Institute of Entomology, Shenyang Normal University. [source]


INSECT SCIENCE, Issue 2 2001
XUE Wan-qi
Abstract Five new species of the genus Coenosia Meigen, namely C. subflaviseta, C. subgracilis, C. parva C. aurea, and C. zhooi, are described from the Xinjiang Autonomous Region, China. The type specimen of C. parva is kept in the Department of Biology, Shenyang Normal University, and the others are kept in the Institute of Zoology, Chinese Academy of Sciences. [source]


INSECT SCIENCE, Issue 2 2000
ZHANG Run-jie
Abstract, Effects of temperature on population parameters and the intrinsic rate of natural increase of the leafminer, Liriomyza sativae Blanchard, were studied at constant temperatures, 15, 20, 25, 30 and 3593 80% RH and a photoperiod of 12:12 (L:D) in the laboratory with Phaseolus vulgaris as the host plant. Developmental time of the immature stage decreased from 38 d at 15C to lld at 3593 Regression equations relating temperature (t) to development rates (y) for egg, larval and pupal stages, were y = 1.7862t - 13.841, y = 1.162t - 4.946 and y= 0.634t - 5.146, respectively. Longevity of female adult decreased from 20 d at 15°C to 9 d with temperature up to 35C The most favorable temperature range for reproduction was 20°C - 30oC in which the fecundity ranged from 158 to 282 eggs per female. The lowest total mortality was 9% at 25oC and the highest was 49% at 35 93 High intrinsic rate of natural increase (rm) was 0.27 and high net reproductive rate (R0) was 116.8 at temperature range between 25 t and 30 t indicating that this range was optimal for population growth and that population density might increase 117 times per generation under this temperature condition. Mean generation time (T) and time for population to double (t) decreased as temperature increased, showing a negative linear trend with temperature. The relationship between finite rate of increase (A) and temperature, however, was a positive linear regression. [source]

Significance of Specimen Databases from Taxonomic Revisions for Estimating and Mapping the Global Species Diversity of Invertebrates and Repatriating Reliable Specimen Data

More specifically, we demonstrate for a specimen database assembled during a revision of the robber-fly genus Euscelidia (Asilidae, Diptera) how nonparametric species richness estimators (Chao1, incidence-based coverage estimator, second-order jackknife) can be used to (1) estimate global species diversity, (2) direct future collecting to areas that are undersampled and/or likely to be rich in new species, and (3) assess whether the plant-based global biodiversity hotspots of Myers et al. (2000) contain a significant proportion of invertebrates. During the revision of Euscelidia, the number of known species more than doubled, but estimation of species richness revealed that the true diversity of the genus was likely twice as high. The same techniques applied to subsamples of the data indicated that much of the unknown diversity will be found in the Oriental region. Assessing the validity of biodiversity hotspots for invertebrates is a formidable challenge because it is difficult to decide whether species are hotspot endemics, and lists of observed species dramatically underestimate true diversity. Lastly, conservation biologists need a specimen database analogous to GenBank for collecting specimen records. Such a database has a three-fold advantage over information obtained from digitized museum collections: (1) it is shown for Euscelidia that a large proportion of unrevised museum specimens are misidentified; (2) only the specimen lists in revisionary studies cover a wide variety of private and public collections; and (3) obtaining specimen records from revisions is cost-effective. Resumen:,Sostuvimos que los millones de registros de especimenes publicados en miles de revisiones taxonómicas en décadas anteriores son una fuente de información costo-efectiva de importancia crítica para la incorporación de invertebrados en decisiones de investigación y conservación. Más específicamente, para una base de datos de especimenes de moscas del género Euscelidia (Asilidae, Diptera) demostramos como se pueden utilizar estimadores no paramétricos de riqueza de especies (Chao 1, estimador de cobertura basado en incidencia, navaja de segundo orden) para (1) estimar la diversidad global de especies, (2) dirigir colecciones futuras a áreas que están sub-muestreadas y/o probablemente tengan especies nuevas y (3) evaluar si los sitios globales de importancia para la biodiversidad basados en plantas de Myers et al. (2000) contienen una proporción significativa de invertebrados. Durante la revisión de Euscelidia el número de especies conocidas fue más del doble, pero la estimación de riqueza de especies reveló que la diversidad real del género probablemente también era el doble. Las mismas técnicas aplicadas a las sub-muestras de datos indicaron que gran parte de la diversidad no conocida se encontrará en la Región Oriental. La evaluación de la validez de sitios de importancia para la biodiversidad de invertebrados es un reto formidable porque es difícil decidir si las especies son endémicas de esos sitios y si las listas de especies observadas subestiman dramáticamente la diversidad real. Finalmente, los biólogos de la conservación requieren de una base de datos de especimenes análoga a GenBank, para obtener registros de especimenes. Dicha base de datos tiene una triple ventaja sobre la información obtenida de colecciones de museos digitalizadas. (1) Se muestra para Euscelidia que una gran proporción de especimenes de museo no revisados están mal identificados. (2) Sólo las listas de especimenes en estudios de revisión cubren una amplia variedad de colecciones privadas y públicas. (3) La obtención de registros en revisiones es costo-efectiva. [source]

Conservation of Insect Diversity: a Habitat Approach

Jennifer B. Hughes
To explore the feasibility of basing conservation action on community-level biogeography, we sampled a montane insect community. We addressed three issues: (1) the appropriate scale for sampling insect communities; (2) the association of habitat specialization,perhaps a measure of extinction vulnerability,with other ecological or physical traits; and (3) the correlation of diversity across major insect groups. Using malaise traps in Gunnison County, Colorado, we captured 8847 Diptera (identified to family and morphospecies), 1822 Hymenoptera (identified to morphospecies), and 2107 other insects (identified to order). We sampled in three habitat types,meadow, aspen, and conifer,defined on the basis of the dominant vegetation at the scale of hundreds of meters. Dipteran communities were clearly differentiated by habitat type rather than geographic proximity. This result also holds true for hymenopteran communities. Body size and feeding habits were associated with habitat specialization at the family level. In particular, habitat generalists at the family level,taxa perhaps more likely to survive anthropogenic habitat alteration,tended to be trophic generalists. Dipteran species richness was marginally correlated with hymenopteran species richness and was significantly correlated with the total number of insect orders sampled by site. Because these correlations result from differences in richness among habitat types, insect taxa may be reasonable surrogates for one another when sampling is done across habitat types. In sum, community-wide studies appear to offer a practical way to gather information about the diversity and distribution of little-known taxa. Resumen:No existe ni el tiempo ni los recursos para diseñar planes de conservación para cada especie, particularmente para los taxones poco estudiados, no carismáticas, pero ecológicamente importantes que componen la mayoría de la biodiversidad. Para explorar la factibilidad de basar acciones de conservación en biogegrafía a nivel comunitario, muestreamos una comunidad de insectos de montaña. Evaluamos tres aspectos: (1) la escala adecuada para el muestreo de comunidades de insectos; (2) la asociación de especialización de hábitat,quizá una medida de vulnerabilidad de extinción,con otras características ecológicas o físicas; y (3) la correlación de la diversidad a lo largo de los grupos principales de insectos. Mediante el uso de trampas en el condado Gunnison, en Colorado, capturamos 8847 dípteros (identificados a nivel de familia y morfoespecies), 1822 himenópteros (identificadas hasta morfoespecies) y 2107 otros insectos (identificados a nivel de orden). Muestreamos tres tipos de hábitats,vega, álamos temblones y coníferas,definidos en base a la vegetación dominante a escala de cientos de metros. Las comunidades de dípteros estuvieron claramente diferenciadas por tipos de hábitat y no por la proximidad geográfica. Este resultado también se mantiene para las comunidades de himenópteros. El tamaño del cuerpo y los hábitos alimenticios estuvieron asociados con la especialización del hábitat a nivel de familia. En particular, los generalistas de hábitat a nivel de familia,los taxones que posiblemente tengan mayor probabilidad de sobrevivir alteraciones antropogénicas del hábitat,tendieron a ser generalistas tróficos. La riqueza de las especies de dípteros estuvo marginalmente correlacionada con la riqueza de especies de himenópteros y estuvo significativamente correlacionada con el número total de órdenes de insectos muestreadas por sitio. Debido a que estas correlaciones resultaron de diferencias en la riqueza de especies entre tipos de hábitats, los taxones de insectos podrían ser substitutos mutuos razonables cuando se muestrea entre diferentes tipos de hábitats. En resumen, los estudios a lo largo de comunidades parecen ofrecer una forma práctica de recolectar información sobre la diversidad y distribución de los taxones poco estudiados. [source]

Remarks on the morphology and biology of Cleigastra apicalis (Meigen, 1826) (Diptera, Scathophagidae)

ACTA ZOOLOGICA, Issue 4 2006
Maria Grochowska
Abstract The egg, second- and third-instar larvae and puparium of Cleigastra apicalis are described for the first time. All pre-imaginal stages are found on stems of the common reed affected by flies of the genera Lipara and Platycephala and the butterfly Arenostola phragmitidis. The larvae feed on dead plant and animal tissue and the excreta of other insects that live inside the stems of the common reed. Exceptionally they will scrape living plant tissue. The pupa is the overwintering stage. [source]

Flies and concealed nectar sources: morphological innovations in the proboscis of Bombyliidae (Diptera)

ACTA ZOOLOGICA, Issue 3 2002
N. U. Szucsich
Abstract Bee-flies (Bombyliidae) have morphological adaptations of the mouthparts to particular floral traits. To investigate this the short, plesiomorphic proboscis of Hemipenthes morio was compared with the long, apomorphic proboscis of Bombylius major. A novel feeding position enables B. major to use flowers that open to the side as additional nectar sources. The new horizontal feeding position is enabled by the prolonged ventral base of the proboscis. Bombylius major exploits deep corolla tubes with an elongate proboscis, and an increased efficiency in both the suction pumps and the sealing mechanisms of the proboscis. The exploitation of narrow corolla tubes is made possible by the shift from a sponging feeding mode, exhibited by H. morio, to the exclusively sucking mode in B. major. Besides quantitative changes in the proportions of the different proboscis components, labellar movements as well as the structures of saliva distribution are changed along with this shift. The labial musculature of B. major does not significantly differ from the plesiomorphic state, since both examined species do not only feed on nectar, but also on pollen. [source]

Nested distributions of bat flies (Diptera: Streblidae) on Neotropical bats: artifact and specificity in host-parasite studies

ECOGRAPHY, Issue 3 2009
Bruce D. Patterson
We examined the structure of ectoparasitic bat fly infestations on 31 well-sampled bat species, representing 4 Neotropical families. Sample sizes varied from 22 to 1057 bats per species, and bat species were infested by 4 to 27 bat fly species. Individual bats supported smaller infracommunities (the set of parasites co-occurring on an individual host), ranging from 1 to 5 fly species in size, and no bat species had more than 6 bat fly species characteristically associated with it (its primary fly species). Nestedness analyses used system temperature (BINMATNEST algorithm) because it is particularly well-suited for analysis of interaction networks, where parasite records may be nested among hosts and host individuals simultaneously nested among parasites. Most species exhibited very low system temperatures (mean 3.14°; range 0.14,12.28°). Simulations showed that nested structure for all 31 species was significantly stronger than simulated values under 2 of the 3 null hypotheses, and about half the species were also nested under the more stringent conditions of the third null hypothesis. Yet this structure disappears when analyses are restricted to "primary" associations of fly species (flies on their customary host species), which exclude records thought to be atypical, transient, or potential contaminants. Despite comprising a small fraction of total parasite records, such anomalies represent a considerable part of the statistical state-space, offering the illusion of significant ecological structure. Only well understood and well documented systems can make distinctions between primary and other occurrence records. Generally, nestedness appears best developed in host-parasite systems where infestations are long-term and accumulate over time. Dynamic, short-term infestations by highly mobile parasites like bat flies may appear to be nested, but such structure is better understood in terms of host specificity and accidental occurrences than in terms of prevalence, persistence, or hierarchical niche relations of the flies. [source]

The species-area relationship in the hoverfly (Diptera, Syrphidae) communities of forest fragments in southern France

ECOGRAPHY, Issue 2 2006
Annie Ouin
The effect of forest fragmentation was studied in hoverfly communities of 54 isolated forests (0.14,171 ha) in south west France. The positive relationship between species richness and wood patch area was investigated by testing the three hypotheses usually put forward to explain it: 1) the sampling effect hypothesis, 2) the patch heterogeneity hypothesis, 3) the hypothesis of equilibrium between distance from other patch (colonisation) and surface area of the patch (extinction). The syrphid species were divided into 3 ecological groups, based on larval biology as summarized in the "Syrph the Net" database: non forest species, facultative forest species and forest species. A total of 3317 adults belonging to 100 species, were captured in the 86 Malaise traps. Eight species were non forest (N=16), 65 facultative forest (N=2803) and 27 forest species (N=498). Comparison of the slopes of the species-area curves for species richness and species density per forest patch showed a strong sampling effect in the species-area relationship. Wood patch heterogeneity increased with wood patch area and positively influenced hoverflies richness. Less isolated wood patches presented high richness of forest species and low richness of non forest species. Only forest species richness seemed to respond to the equilibrium between surface area and isolation. Depending on which hypothesis explained best the species-area relationship, management recommendations to mitigate fragmentation effects were formulated at various spatial scales and for different stakeholders. [source]

Can host-range allow niche differentiation of invasive polyphagous fruit flies (Diptera: Tephritidae) in La Réunion?

Abstract 1.,Biological invasions bring together formerly isolated insect taxa and allow the study of ecological interactions between species with no coevolutionary history. Among polyphagous insects, such species may competitively exclude each other unless some form of niche partitioning allows them to coexist. 2.,In the present study, we investigate whether the ability to exploit different fruits can increase the likelihood of coexistence of four species of polyphagous Tephritidae, one endemic and three successive invaders, in the island of La Réunion. In the laboratory, we studied the performances of all four species on the four most abundant fruit resources in the island, as well as the relative abundances of fly species on these four fruit species in the field. We observe no indication of niche partitioning for any of the four abundant fruits. 3.,Analyses of an extensive field data series suggest that: (i) the four fly species largely overlap in fruit exploitation, once climatic effects are accounted for; (ii) however, one species (Ceratitis capitata) can exploit rare fruit species that are not exploited by others present in the same climatic niche; and (iii) the endemic species C. catoirii, now nearly extinct in La Réunion, has no private niche with respect to either climatic range or fruit use. 4.,On the whole, with the possible exception of C. capitata, the results point to a limited role of fruit diversity in encouraging coexistence among polyphagous tephritids recently brought into contact by accidental introductions. [source]

Feeding by Hessian fly [Mayetiola destructor (Say)] larvae does not induce plant indirect defences

Abstract 1.,Recent research has addressed the function of herbivore-induced plant volatiles in attracting natural enemies of feeding herbivores. While many types of insect herbivory appear to elicit volatile responses, those triggered by gall insects have received little attention. Previous work indicates that at least one gall insect species induces changes in host-plant volatiles, but no other studies appear to have addressed whether gall insects trigger plant indirect defences. 2.,The volatile responses of wheat to feeding by larvae of the Hessian fly Mayetiola destructor (Say) (Diptera: Cecidomyiidae) were studied to further explore indirect responses of plants to feeding by gall insects. This specialist gall midge species did not elicit a detectable volatile response from wheat plants, whereas a generalist caterpillar triggered volatile release. Moreover, Hessian fly feeding altered volatile responses to subsequent caterpillar herbivory. 3.,These results suggest that Hessian fly larvae exert a degree of control over the defensive responses of their host plants and offer insight into plant-gall insect interactions. Also, the failure of Hessian fly larvae to elicit an indirect defensive response from their host plants may help explain why natural enemies, which often rely on induced volatile cues, fail to inflict significant mortality on M. destructor populations in the field. [source]

Pollution by conspecifics as a component of intraspecific competition among Aedes aegypti larvae

Stéphanie Bédhomme
Abstract., 1. The role of pollution by conspecifics in the costs associated with larval intraspecific competition was investigated for Aedes aegypti (Diptera: Culicidae). 2. The growth of larval A. aegypti mosquitoes reared in clean water and water in which another larva had previously grown was compared; this procedure eliminates interactions through food consumption between competitors and allows the effects of other processes to be expressed. 3. A cost of growing in polluted water was found: this cost was expressed as an increase in developmental time and a reduction of adult longevity when starved, starved adult dry weight, and wing length. 4. Contrary to previously reported results of an experiment allowing for competition for food, these costs were not expressed in a sex-specific manner and were independent of the sex of the polluter. 5. It was thus demonstrated that competition arises from both resource depletion and other effects that result in deterioration of the environment, with chemical pollution of the environment being the most likely cause. [source]

Coexistence of natural enemies in a multitrophic host,parasitoid system

Michael B. Bonsall
Abstract., 1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host,parasitoid assemblage. 2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored. 3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae, was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid. 4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence. [source]

Adult mortality and oviposition rates in field and captive populations of the blowfly Lucilia sericata

K. M. Pitts
Abstract., 1. Adult mortality and oviposition rates were determined for populations of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae). This species is of economic importance as the primary agent of sheep myiasis throughout north-western Europe. 2. Populations of marked flies in six, 1 m3, outdoor field cages and unmarked wild flies at two farms in south-west England were studied simultaneously between May and September 1998. 3. In the field, wild female L. sericata were caught and aged using a combination of wing-fray and ovarian dissection techniques. Survivorship analysis gave estimates of mortality of 1.94% (± 0.037) and 2.09% (± 0.044) per day-degree and mean life expectancy of 51.5 and 47.9 day-degrees above a threshold of 11 °C, at the two farms studied. Mean lifetime reproductive output in the field was estimated to be 159.6 and 138.4 eggs per female at the two farms respectively. 4. The survivorship of cohorts of marked female flies in cages was followed by counting the number of dead individuals each day; the mortality rate of these flies was 0.81% per day-degree (± 3.49 × 10,4%) and the mean life expectancy was 123.1 day-degrees above a threshold of 11 °C. Mortality rate was shown to increase significantly with average ambient temperature and relative humidity lagged for two sample periods (approximately 10 days). Oviposition rate also increased with average temperature but declined with average relative humidity. A best-fit multiple regression model incorporating both ambient temperature and humidity explained 60.5% of the variance in the pattern of oviposition. 5. The differences between the field and cage populations highlight the caution required when extrapolating life-history parameters from artificial to natural habitats. [source]

A review of relationships between interspecific competition and invasions in fruit flies (Diptera: Tephritidae)

Pierre-Francois Duyck
Abstract., 1. A number of invasions in the family Tephritidae (fruit flies) have been observed worldwide despite quarantine procedures. In this review, the potential importance of interspecific competition and competitive displacement among different tephritid species is evaluated in the context of recent invasions. 2. Where polyphagous tephritid species have been introduced in areas already occupied by a polyphagous tephritid, interspecific competition has resulted in a decrease in number and niche shift of the pre-established species. No reciprocal invasions have been observed. 3. The data on tephritid invasions seem to support a hierarchical mode of competition; however, complete exclusion usually did not occur. Indeed, tephritid distribution and abundance are markedly structured by various abiotic (mostly climatic) and biotic (host plants) factors. 4. The primary determinant of competitive interactions in near-optimal conditions, such as lowlands with abundant fruit plantations, is probably the life-history strategy. The r,K gradient could be used as a predictor of potential invaders, because K traits (such as large adult size) may favour both exploitation and interference competition. 5. For future research, a better understanding of competition mechanisms seems essential. Different species competing in the same area should be compared with respect to: (i) demographic parameters, (ii) the outcome of experimental co-infestations on the same fruit, and (iii) behavioural and chemical interference mechanisms. [source]

Phorid fly parasitoids of invasive fire ants indirectly improve the competitive ability of a native ant

Natasha J. Mehdiabadi
Abstract., 1.,The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), is an invasive species of south-eastern U.S.A. Since its introduction from South America approximately 70 years ago, this pest has devastated natural biodiversity. 2.,Due to such ecological costs, Pseudacteon phorid fly parasitoids (Diptera: Phoridae) from South America are being introduced into the U.S.A. as a potential biological control agent. Here, the indirect effects of these specialised parasitoids on an interspecific native ant competitor, Forelius mccooki (Hymenoptera: Formicidae), are evaluated. 3.,Over the course of a 50-day laboratory experiment, the results show that the native ant improved aspects of exploitative, but not interference, competition when S. invicta -attacking flies were present compared with when they were absent. 4.,Forelius mccooki colonies from the phorid treatment had approximately twice as many foragers at food baits relative to controls; however, there was no significant difference in interference aspects of competition or native ant colony growth between the two treatments. 5.,These results suggest that the S. invicta -specialised parasitoids help shift the competitive balance more in favour of F. mccooki than if these flies were not present; however, this competitive advantage does not translate into increased colony growth after 50 days. These laboratory findings are interpreted with regard to the more complex interactions in the field. [source]

Gall size determines the structure of the Rabdophaga strobiloides host,parasitoid community

Brian H. Van Hezewijk
Abstract., 1.,The relationship between gall size and mortality of the willow pinecone gall midge Rabdophaga strobiloides (Diptera: Cecidomyiidae) was examined by determining the fate of all galls in a 30-ha area in central Alberta, Canada over 4 years. It was found that gall size has a large effect on the type and intensity of mortality experienced by the gall midge, and consequently this factor has the potential to influence the dynamics of the host,parasitoid interaction through the creation of phenotypic refuges. 2.,Total midge mortality ranged from 51% to 78% over the course of the study and was dominated by parasitism by Torymus cecidomyiae (Hymenoptera: Torymidae) and Gastrancistrus sp. (Hymenoptera: Pteromalidae) as well as predation by birds. Gall size had a strong, non-linear effect on the attack rates of each of these natural enemies. 3.,Birds attacked the smallest size classes. Torymus cecidomyiae preferentially attacked medium diameter galls and thus avoided predation by birds in smaller galls. Gastrancistrus sp. preferentially attacked the largest galls and consequently suffered lower rates of predation by both T. cecidomyiae and birds. 4.,This study emphasises the importance of understanding the interactions among mortality factors in order to describe adequately the susceptibility of R. strobiloides to parasitism and predation, and ultimately its population dynamics. [source]

Clutch size in frugivorous insects as a function of host firmness: the case of the tephritid fly Anastrepha ludens

Francisco Díaz-Fleischer
Abstract. 1.,Optimal clutch size theory predicts that individuals will oviposit the number of eggs that increases their fitness. In Anastrepha ludens Loew (Diptera: Tephritidae), females oviposit larger clutches in unripe (firm) fruits than in ripe (soft) fruits. The following hypotheses were tested: (1) Using fruit firmness as an indicator of fruit quality, A. ludens females vary the number of eggs per clutch every time they reach an oviposition decision. (2) Maximising offspring survival with respect to either unripe or ripe fruit requires placing large clutches in firm fruit and smaller clutches in soft fruit. 2.,Agar spheres were used as artificial hosts. Three agar concentrations resulted in three degrees of firmness. Mango fruits Mangifera indica L. served as natural hosts. Ripe and unripe fruits were used to test soft and firm host conditions respectively. Females laid significantly larger clutches in the firmer artificial hosts than in the softer hosts. They also laid significantly more eggs in artificial hosts without sugar than in hosts with sugar. Firm (unripe) mangoes also received significantly larger clutches than soft (ripe) mangoes. 3.,When an individual female was first presented with a firm artificial host, it laid a large clutch. If subsequently offered a soft host, the female laid a significantly smaller clutch. Finally, if again offered a firm host, clutch size was increased significantly. 4.,Possible trade-offs in offspring fitness were explored in ripe and unripe mangoes by measuring offspring egg-to-adult survival, pupal weight, mean adult longevity, and fecundity. Despite the fact that larval survival was greater in soft fruit than in firm fruit, parameters such as pupal weight, mean longevity, and fecundity of adults stemming from both fruit types did not differ significantly. 5.,A probable trade-off between high offspring mortality caused by host unsuitability and low offspring and adult mortality caused by parasitism and predation is discussed as the reason for the exploitation of sub-optimal hosts. [source]

Using age grading by wing injuries to estimate size-dependent adult survivorship in the field: a case study of the yellow dung fly Scathophaga stercoraria

Dieter U. Burkhard
Abstract 1. Studies of natural selection depend on estimates of longevity and mortality in the wild. In small and mobile species such as insects, direct, mark,recapture (resight), studies are difficult to perform because individuals cannot be tracked easily. 2. It was investigated whether age grading based on wing injuries alone can be used to estimate size-specific survivorship in the field in the yellow dung fly Scathophaga stercoraria (L.) (Diptera: Scathophagidae). 3. The accumulation of different types of wing injury throughout the spring and autumn flight seasons for both sexes was recorded: tears, notches (both reflecting regular wear), and large missing areas (probably due to intra- and inter-specific interactions). 4. Female longevity increased with body size in both spring and autumn, whereas male longevity increased slightly with size in spring but decreased in autumn. 5. The two sexes and males of different size classes accumulated the various types of wing injury differentially, presumably due to differential patterns of intraspecific interactions. Additionally, body size exhibited a seasonal pattern, complicating interpretation of the relationship between body size and wing injuries. 6. It is therefore concluded that estimating adult viability selection on body size using wing injuries is problematic in dung flies, and potentially also in other species. It is suggested that before this method is applied in any particular species, pilot studies should be conducted to verify whether wing injuries accumulate equally in all classes of individuals of interest. In addition, it is necessary to investigate the causes of different types of wing injury. [source]

Community effects of praying mantids: a meta-analysis of the influences of species identity and experimental design

William F. Fagan
Abstract ,1. Generalist arthropod predators are ubiquitous in terrestrial ecosystems but experimental studies have yielded little agreement as to their effects on prey assemblages. Drawing on results from a suite of experimental field studies, a meta-analysis was conducted of the impact of praying mantids (Mantodea: Mantidae) on arthropod assemblages in order to identify predictable and unpredictable effects of these extremely generalised predators. 2. Results across different experiments were synthesised using the log response ratio framework, with a focus on quantifying net mantid impacts on arthropod density across taxonomic orders and trophic levels of arthropods, paying special attention to the contribution of mantid species identity and experimental design variables, such as the use of cages, length of experiment, and manipulated mantid density. 3. Calculated on a per mantid-day basis, the net impacts of Tenodera sinensis on arthropod density were generally weaker but more predictable than the effects of Mantis religiosa. Mantids in general had weak negative effects on density for most taxa but exhibited strong negative and positive effects on some taxa. Tenodera sinensis tended to have negative effects on Homoptera, Diptera, and Hemiptera and herbivores as a group, however M. religiosa exhibited greater variation in response of different taxa that appeared to be affected more strongly by experimental design. The effects of Stagmomantis carolina tended to be negative or non-significant. 4. Experimental cages had little influence on either the sign or magnitude of net community impacts for T. sinensis, however cage experiments reversed the sign of the mean effect for two of six taxonomic orders when the experimental predator was M. religiosa. Cages also increased the variability of effect size greatly for M. religiosa but not for T. sinensis. 5. It was concluded that it is possible to use log response ratios to determine general, predictable trends in a well-studied system. Similar meta-analyses of generalist predator effects in other systems should produce predictions of how these predators influence food webs, an important step towards defining more clearly the influences of generalist predators on community structure and dynamics. [source]

Contrasting frequencies of parasitism and host mortality among phorid and conopid parasitoids of bumble-bees

Michael C. Otterstatter
Abstract 1. Phorid (Diptera, Phoridae) and conopid (Diptera, Conopidae) parasitism among four North American bumble-bee (Hymenoptera, Apidae) species was investigated. Male bumble-bees experienced a significantly higher incidence of parasitism by the phorid, Apocephalus borealis Brues, and a significantly lower incidence of parasitism by the conopid, Physocephala texana Williston, than did workers. 2. The incidence of parasitism by A. borealis and P. texana varied between bumble-bee sexes and species in patterns that did not reflect differences in relative host abundance. Differences in foraging behaviour between bumble-bee workers and males, as well as between species, may explain these results. 3. Bumble-bee workers and males parasitised by A. borealis had significantly shorter lifespans than unparasitised bees. Based on previous estimates of bumble-bee mortality, A. borealis parasitism may reduce worker lifespans by up to 70%. In contrast, the mortality rate of bees parasitised by P. texana was not significantly different from that of unparasitised bees. 4. These results contrast with previous work highlighting the importance of conopid parasitism to bumble-bee populations, and suggest that phorid parasitism may impose greater costs to bumble-bees than does conopid parasitism in local populations. [source]

Do parasitoids diversify in response to host-plant shifts by herbivorous insects?

James T. Cronin
Summary 1. For herbivorous insects, the incorporation of a novel host into the diet, and subsequent formation of distinct host associations (races), is thought to be a significant early step in the speciation process. While many studies have addressed this issue, virtually nothing is known about the evolutionary response of natural enemies to herbivore host-race formation. 2. The hypothesis that the parasitoid wasp Eurytoma gigantea (Hymenoptera: Eurytomidae) has formed host races in direct response to the host shift and subsequent host-race formation by its host, the gallmaker Eurosta solidaginis (Diptera: Tephritidae) was tested. Emergence time, mating preference, and female oviposition preference were determined for parasitoids derived from galls of each Eurosta host race. 3. Male and female E. gigantea overlap broadly in their emergence times from each Eurosta host race, suggesting that there is no phenological barrier to gene flow. 4. In choice experiments, female parasitoids did not mate assortatively: females that emerged from one Eurosta host race were equally likely to mate with males from either Eurosta host race. 5. Oviposition behaviour experiments revealed that female parasitoids do not prefer to oviposit on their host race of origin and that there is no overall preference for one host race, even though fitness is higher when parasitoids are reared from Eurosta galls of the Solidago gigantea host race than when reared from Eurosta galls of the Solidago altissima host race. 6. These results suggest that E. gigantea has not diverged in parallel with its host in response to the herbivore host-plant shift. Further studies are needed before the ubiquity of this diversification mechanism can be evaluated fully. [source]

The role of resources and natural enemies in determining the distribution of an insect herbivore population

Iain S. Williams
Summary 1. Both resources and natural enemies can influence the distribution of a herbivore. The ideal free distribution predicts that herbivores distribute themselves to optimise utilisation of resources. There is also evidence of herbivores seeking out refuges that reduce natural enemy attack (enemy-free space). Which of these theories predominates in a thistle,tephritid Terellia ruficauda (Diptera: Tephritidae),parasitoid interaction is examined. 2. The plant, Cirsium palustre, had a contagious distribution approximated by the negative binomial distribution. Terellia ruficauda foraged preferentially and oviposited on isolated plants although its larvae gained neither nutritional benefit nor reduced natural enemy pressure from such behaviour. 3. Parasitoids of T. ruficauda foraged and oviposited more frequently on isolated than on crowded T. ruficauda, resulting in inverse density-dependent parasitoid attack at all spatial scales examined. Neither the herbivore nor natural enemies distributed themselves according to the predictions of the ideal free distribution and the herbivore did not oviposit to reduce natural enemy attack. 4. Extrapolating from the theoretical predictions of the ideal free distribution and enemy-free space to the field requires considerable caution. Terellia ruficauda and its parasitoids appear to select their oviposition sites to spread the risk of losses through factors (e.g. mammal herbivory) that may damage dense clusters of C. palustre. [source]

The influence of host plant variation and intraspecific competition on oviposition preference and offspring performance in the host races of Eurosta solidaginis

Timothy P. Craig
Summary 1. A series of experiments was conducted to measure the impact of plant genotype, plant growth rate, and intraspecific competition on the oviposition preference and offspring performance of the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and Solidago gigantea (Asteraceae). Previous research has shown that both host races prefer to oviposit on their own host plant where survival is much higher than on the alternate host plant. In this study, neither host race showed any relationship between oviposition preference and offspring performance in choosing among plants of their natal host species. 2. The larval survival of both host races differed among plant genotypes when each host race oviposited on its natal host species. In one experiment, altissima host race females showed a preference among plant genotypes that was not correlated with offspring performance on those genotypes. In all other experiments, neither the altissima nor gigantea host race demonstrated a preference for specific host plant genotypes. 3. Eurosta solidaginis had a preference for ovipositing on rapidly growing ramets in all experiments, however larval survival was not correlated with ramet growth rate at the time of oviposition. 4. Eurosta solidaginis suffered high mortality from intraspecific competition in the early larval stage. There was little evidence, however, that females avoided ovipositing on ramets that had been attacked previously. This led to an aggregated distribution of eggs among ramets and strong intraspecific competition. 5. There was no interaction among plant genotype, plant growth rate, or intraspecific competition in determining oviposition preference or offspring performance. [source]

Methoprene modulates the effect of diet on male melon fly, Bactrocera cucurbitae, performance at mating aggregations

Ihsan ul Haq
Abstract The effect of access to dietary protein (P) (hydrolyzed yeast) and/or treatment with a juvenile hormone analogue, methoprene (M), (in addition to sugar and water) on male aggregation (lekking) behaviour and mating success was studied in a laboratory strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Six-day-old males were treated with (1) protein and methoprene (M+P+), (2) only protein (M,P+), or (3) only methoprene (M+P,), and compared with 14-day-old sexually mature untreated males (M,P,). The lekking behaviour of the four groups of males when competing for virgin sexually mature females (14,,16 days old) was observed in field cages. The following parameters were measured at male aggregations: lek initiation, lek participation, males calling, male,male interaction, female acceptance index, and mating success. For all these parameters, the M+P+ males significantly outperformed the other males. Moreover, for all parameters, there was a similar trend with M+P+ > M,P+ > M,P, > M+P,. More M+P+ males called and initiated and participated in lek activities than all other types of male, which resulted in higher mating success. They had also fewer unsuccessful copulation attempts than their counterparts. Whereas treatment with methoprene alone had a negative effect in young males with only access to sugar, access to dietary protein alone significantly improved young male sexual performance; moreover, the provision of methoprene together with protein had a synergistic effect, improving further male performance at leks. The results are of great relevance for enhancing the application of the sterile insect technique (SIT) against this pest species. The fact that access to dietary protein and treatment of sterile males with methoprene improves mating success means that SIT cost-effectiveness is increased, as more released males survive to sexual maturity. [source]

Small-scaled geographical variation in life-history traits of the blowfly Calliphora vicina between rural and urban populations

C. C. Hwang
Abstract The impact of the urban heat-island effect, the warming-up of an urban area caused by human activity, on the blowfly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) was examined at two British sites, 30 km apart. Waterloo in Central London is a highly urbanised built-up area, whereas Box Hill in the county of Surrey is a rural pasture and woodland location. The phenotypic plasticity of 12 C. vicina cultures, originated from single females from each of the two sites, was measured using three developmental characters: adult body size (represented as the length of the cross vein dm-cu of the right wing), development time as accumulated degree-days (ADD), and growth rate (length of dm-cu/ADD), along a constant temperature series of 16, 20, 24, and 28 °C in the laboratory. The blowflies from Box Hill had the same ADD as those from Waterloo, but showed a significantly larger adult size and growth rate at lower temperatures, suggesting the existence of local adaptations that may be caused by the differing levels of urbanisation between the two studied sites. Not surprisingly, a trade-off between adult size and development time was found. Females showed longer development times than males at all four temperatures, indicating they may need to ingest more food as larvae to furnish ovarioles and increase fecundity. However, females had larger adult size than males at 16 and 20 °C but a reverse at 28 °C, suggesting that females may be more cold-adapted than males. [source]

Control of aphids on wheat by generalist predators: effects of predator density and the presence of alternative prey

Katja Oelbermann
Abstract There is evidence for both positive and negative effects of generalist predators on pest populations and the various reasons for these contrasting observations are under debate. We studied the influence of a generalist predator, Pardosa lugubris (Walckenaer) (Araneae: Lycosidae), on an aphid pest species, Rhopalosiphum padi (L.) (Hemiptera: Aphididae; low food quality for the spider), and its host plant wheat, Triticum spec. (Poaceae). We focused on the role of spider density and the availability of alternative prey, Drosophila melanogaster Meigen (Diptera: Drosophilidae; high food quality). The presence of spiders significantly affected plant performance and aphid biomass. Alternative prey and spider density strongly interacted in affecting aphids and plants. High spider density significantly improved plant performance but also at low spider density plants benefited from spiders especially in the presence of alternative prey. The results suggest that generalist arthropod predators may successfully reduce plant damage by herbivores. However, their ability to control prey populations varies with predator nutrition, the control of low-quality prey being enhanced if alternative higher-quality prey is available. [source]