Effects of floral resources on fitness of the parasitoids Trichogramma exiguum (Hymenoptera: Trichogrammatidae) and Cotesia congregata (Hymenoptera: Braconidae)
ABSTRACT This study was conducted to determine if floral resources enhanced longevity and fecundity of the egg parasitoid Trichogramma exiguum Pinto & Platner and longevity of the larval parasitoid Cotesia congregata (Say). Newly eclosed (⩽12 h) female wasps were provisioned with fennel (Foeniculum vulgare P. Mill.) or buckwheat (Fagopyrum esculentum Moench) flowers or one of two controls: honey or water. Wasps were monitored daily until all had died. Daily egg production by T. exiguum was monitored using Ephestia kuehniella Keller egg cards. Longevity of both T. exiguum (6.7 d) and C. congregata (5.1 d) provided buckwheat flowers was increased approximately 8.5-fold compared with wasps provided only water. Buckwheat-provisioned T. exiguum exhibited 2-fold greater longevity than those provided fennel. Longevity of C. congregata provisioned with fennel and honey was not statistically different. Water-provisioned T. exiguum and C. congregata exhibited the shortest longevity (0.8 and 0.6 d, respectively). Total fecundity was 6.3-fold greater in T. exiguum provisioned with buckwheat and 2.3-fold greater in T. exiguum provisioned with fennel than in water controls. Average female to male ratio of progeny over the lifetime of each female was significantly greatest in T. exiguum provisioned with water alone, likely because of sperm depletion in wasps exhibiting greater longevity. Total mean number of female offspring produced was significantly greatest in T. exiguum provided honey or buckwheat flowers although no difference in total female offspring were observed between adults provisioned with buckwheat or fennel flowers. Our results show that provisioning T. exiguum with honey and buckwheat flowers resulted in greater longevity, total fecundity, and lifetime production of female offspring than water alone. Buckwheat flowers also lead to greater longevity in C. congregata.
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ABSTRACT: Nectar is an important food source for adult parasitoids and can increase their longevity and fecundity and hence their parasitization rate. Both floral and extrafloral nectar are used as food sources by parasitoids. While floral nectar exploitation by parasitoids has been extensively studied, little is known on how parasitoids locate extrafloral nectar, nor whether the availability of extrafloral nectar increases parasitization of pests in the field. We conducted a Y-tube olfactometer experiment to determine if the parasitoid Microplitis mediator utilizes olfactory cues to locate the extrafloral nectar of Centaurea cyanus. In addition, we performed a semi-field experiment to investigate whether M. mediator are differentially attracted by C. cyanus offering no nectar, only extrafloral nectar or extrafloral and floral nectar and whether this translates in differential parasitization rates of the cabbage moth, Mamestra brassicae, in close vicinity to the plants. Female M. mediator showed an innate attraction to olfactory cues of open flowers but not to extrafloral nectar of C. cyanus. Under our experimental conditions M. mediator showed higher parasitization rates of M. brassicae larvae in the treatment with both floral nectar and extrafloral nectar compared to the treatment with only extrafloral nectar. Our results indicate that M. mediator may require the floral signals of open flowers to actually locate and exploit the plant’s extrafloral nectaries. This is relevant from an applied point because it demonstrates that accessible (extra)floral nectar sources may be insufficiently exploited if they are not attractive to parasitoids. However, this can be resolved when the accessible nectar is associated with attractive floral signals.Biological Control 07/2013; 66(1):16–20. DOI:10.1016/j.biocontrol.2013.02.007 · 1.87 Impact Factor
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ABSTRACT: The limited availability of sugar sources (e.g., flowers) in greenhouses may affect biological pest control by parasitoid wasps. However, few studies have focused on feeding devices to provide parasitoids with sugar foods. We investigated the accessibility of a yellow-colored bottle-type feeding device to adult Cotesia vestalis (Halliday), a larval endoparasitoid of the diamondback moth Plutella xylostella (L.). All parasitoids died within four days in a room with no sugar source, whereas 66.7 % of individuals survived if a bottle-type feeding device providing honey solution was installed. We also investigated female longevity in response to different sugar solutions presented in a bottle-type feeding device. Honey and sugar mixtures (glucose and fructose) improved female longevity (38.4 and 39.2 days, respectively) much more than water (3.1 days), indicating these feeding devices containing sugar foods to be potentially useful for maintaining C. vestalis in greenhouses where natural food sources are limited.BioControl 12/2014; 59(6):681-688. DOI:10.1007/s10526-014-9611-x · 2.25 Impact Factor
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ABSTRACT: The role biodiversity plays in the provision of ecosystem services is widely recognized, yet few ecological studies have identified characteristics of natural systems that support and maintain ecosystem services. The purpose of this study was to identify landscape variables correlated with natural pest suppression carried out by arthropod natural enemies, predators and parasitoids. We conducted two field experiments, one observational and one experimental, where landscape variables at broad and local scales were measured and related to natural pest suppression. The first experiment measured natural pest suppression at 16 sites across an urban to rural landscape gradient in south central Wisconsin. We found natural enemy diversity positively affected natural pest suppression, whereas flower diversity negatively affected pest suppression. No relationship was found between natural pest suppression and broad scale variables, which measured the percentage of different land cover classes in the surrounding landscape. In the second experiment, we established small (2- by 3-m) replicated plots that experimentally varied flower diversity (0, 1, or 7 species) within a plot. We found no significant relationship between natural pest suppression and the different levels of flower diversity. The fact that we only found differences in natural pest suppression in our first experiment, which measured natural pest suppression at sites separated by larger distances than our second experiment, suggests the more appropriate scale for measuring ecosystem services performed by mobile organisms like insects, is across broad spatial scales where variation in natural enemies communities and the factors that affect them become more apparent.Environmental Entomology 10/2012; 41(5):1077-85. DOI:10.1603/EN11328 · 1.42 Impact Factor