Aphid Honeydew Enhances Parasitoid Longevity to the Same Extent as a High-Quality Floral Resource: Implications for Conservation Biological Control of the Wheat Stem Sawfly (Hymenoptera: Cephidae).

Providing sugar resources for parasitoids is an important component of habitat management approaches to bolster biological control. We screened three flowering cover crop species, and one aphid species, for their potential to increase the longevity of the parasitoid wasp, Bracon cephi (Gahan) (Hymenoptera: Braconidae), an important biological control agent of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae). We found that buckwheat and honeydew from the cereal aphid, Rhopalosiphum padi (Linnaeus) (Hemiptera: Aphididae), increased longevity of B. cephi females by over threefold, while longevity on sunflower and coriander was not significantly different from controls on wheat. The results suggest that incorporating buckwheat into cover crop mixes could enhance parasitoid performance. However, the finding that honeydew associated with a common aphid in wheat provides a suitable resource suggests that a better understanding of the varying quality, and spatial and temporal availability, of aphid honeydew will be a critical consideration in evaluating the potential benefits of managing floral resources for parasitoid conservation in this system.

Do Floral Resources Benefit the Herbivorous Sawfly, Cephus cinctus (Hymenoptera: Cephidae), a Major Pest of Wheat in North America?

Leveraging floral resources to promote biological control requires carefully screening prospective floral species for their suitability not just for natural enemies, but also for targeted pests. Here we examined the influence of access to various sugar resources on Cephus cinctus Norton (Hymenoptera: Cephidae), a major pest of wheat in the northern Great Plains of North America. We conducted greenhouse studies to examine the effect of access to a honey-sucrose solution, three flowering plant species, and aphid honeydew, on the longevity and potential fecundity of C. cinctus. Cephus cinctus longevity increased significantly (females living 1.18-1.25 times as long) in treatments with buckwheat (Fagopyrum esculentum Moench (Polygonales: Polygonaceae)) flowers compared with controls. In contrast, there was no significant effect of two additional mustard species (Capparales: Brassicaceae) tested, canola (Brassica napus L.) and white mustard (Sinapis alba L.), or aphid (Myzus persicae Sulzer (Hemiptera: Aphididae)) honeydew on C. cinctus longevity. Access to buckwheat did not significantly increase the cumulative number of eggs laid by C. cinctus, suggesting that sugar feeding on this plant is unlikely to increase pest impacts. To our knowledge, this is the first published experimental evidence that access to floral resources can increase the adult lifespan of C. cinctus. The results re-inforce previous observations that sugar feeding may be common in Cephus spp. and other Cephidae. Our results further suggest that screening prospective floral species being considered for conservation biological control programs against both C. cinctus and potential parasitoids will be an important precautionary measure in future work.

Phylogeography of the Wheat Stem Sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae): Implications for Pest Management.

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a key pest of wheat in the northern Great Plains of North America, and damage resulting from this species has recently expanded southward. Current pest management practices are inadequate and uncertainty regarding geographic origin, as well as limited data on population structure and dynamics across North America impede progress towards more informed management. We examined the genetic divergence between samples collected in North America and northeastern Asia, the assumed native range of C. cinctus using two mitochondrial regions (COI and 16S). Subsequently, we characterized the structure of genetic diversity in the main wheat producing areas in North America using a combination of mtDNA marker and microsatellites in samples collected both in wheat fields and in grasses in wildlands. The strong genetic divergence observed between North American samples and Asian congeners, in particular the synonimized C. hyalinatus, did not support the hypothesis of a recent American colonization by C. cinctus. Furthermore, the relatively high genetic diversity both with mtDNA and microsatellite markers offered additional evidence in favor of the native American origin of this pest. The genetic diversity of North American populations is structured into three genetic clusters and these are highly correlated with geography. Regarding the recent southern outbreaks in North America, the results tend to exclude the hypothesis of recent movement of damaging wheat stem sawfly populations from the northern area. The shift in host plant use by local populations appears to be the most likely scenario. Finally, the significance of these findings is discussed in the context of pest management.