Interspecific mouthpart length variation and floral visitation in the parasitic wasp genus Agathirsia (Braconidae: Agathidinae)

Authors: PUCCI, T - University Of Kentucky; Jones, Gretchen

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2010
Publication Date: 7/1/2010
Citation: Pucci, T.M., Jones, G.D. 2010. Interspecific mouthpart length variation and floral visitation in the parasitic wasp genus Agathirsia (Braconidae: Agathidinae). Annals of the Entomological Society of America. 103:566-573.

Interpretive Summary: Parasitic wasps control populations of agricultural pests such as corn earworm, black cutworm, and fall armyworm by killing the larval stage and laying their eggs in the carcass of the pest. However, little is known about the host plants on which these beneficial insects feed to ensure their survival. Also, little is known about the relationship of the specialized mouth parts of these wasps in relationship to the flowers on which they feed for nectar. Pollen was removed from museum specimens of 30 Agathirsia (Hymenoptera: Braconidae) wasps and identified to the lowest possible taxonomic rank. Wasps were divided into three categories accordingly to their mouth part length: short (less than 1 mm); medium (1-2 mm); and long (more than 2 mm). pollen from 31 species of Asteraceae (sunflower family) was commonly found on the specimens regardless of mouth part length. Wasps with short mouth parts exhibited different feeding hosts (as indicated by plant pollen) than wasps with medium and long mouth parts, which suggests that elongated mouth parts in Agathirsia are associated with host plant use. There was no significant difference in the plants utilized by male and female wasps. We determined that increased feeding efficiency is the adaptive value of elongate mouth parts in Agathirsia. These results indicate that conservation or augmentation of many Asteraceae species would help maintain and increase population of these beneficial insects and lead to reduced pest infestations in crops.

Technical Abstract: Carbohydrate energy sources are known to be important for many adult parasitic wasps. Floral visitation is commonly observed and the occurrence of specialized mouth part morphology associated with deep nectar extraction exists in many groups. In parasitic wasps, it is not well established what, if any, changes in host plant use are associated with differing mouth part length. In an effort to associate mouth part length to nectar source, pollen was identified from museum specimens of selected species of Agathirsia (Hymenoptera: Braconidae). Despite drastic differences in glossa length, the pollen of several species of Asteraceae were commonly found on specimens regardless of glossa length category. We infer that increased feeding efficiency, as opposed to nectar access, is the adaptive value of elongate glossae in Agathirsia. The short category however exhibited a difference from both the medium and long categories in pollen similarity. This suggests that elongate mouth parts in Agathirsia are associated with a different concentration of host plant use. Males and females exhibited considerable overlap of their common nectar sources and displayed similar pollen richness. Pollen richness was higher in the medium length category compared to the short category but these results are confounded by the fact that the medium lengthed specimens were on average larger bodied.