Subsequent chemical and foraging ecology preferences of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae) reared on two alternate stored product host insects

Authors: MAILLE, JACQUELINE - Kansas State University; ALBIN, CHLO - Kansas State University; HARMAN, RACHEL - Orise Fellow; Hetherington, Matthew; RANABHAT, SABITA - Kansas State University; MONTGOMERY, JAYE - Kansas State University; STOLL, IAN - University Of Missouri; LILLICH, MADISON - Kansas State University; GILLETTE, SAMANTHA - Retired Non ARS Employee; Brabec, Daniel; ZHU, KUN YAN - Kansas State University; Scully, Erin; Gerken, Alison; Morrison Iii, William

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2024
Publication Date: 12/6/2024
Citation: Maille, J.M., Albin, C.E., Harman, R.R., Hetherington, M.C., Ranabhat, S., Montgomery, J., Stoll, I.M., Lillich, M., Gillette, S., Brabec, D.L., Zhu, K., Scully, E.D., Gerken, A.R., Morrison III, W.R. 2024. Subsequent chemical and foraging ecology preferences of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae) reared on two alternate stored product host insects. Biological Control. 200(105665). https://doi.org/10.1016/j.biocontrol.2024.105665.
DOI: https://doi.org/10.1016/j.biocontrol.2024.105665

Interpretive Summary: The parasitic wasp, Theocolax elegans, serves as a promising biocontrol agent of stored product insects, including rice weevil and lesser grain borer. Both stored product pest species are found worldwide and cause significant damage to wheat grain in the USA. Although T. elegans can effectively parasitize two different stored product insect species, it is unclear whether it prefers one over the other and it is unclear whether adult insects prefer the species that they completed their development on. In this study, we examined preference by rearing T. elegans on either rice weevil or lesser grain borer for multiple generations. Behavioral assays revealed that adult wasps that fed on lesser grain borers preferred both lesser grain borers and wheat that had been damaged by lesser grain borers over rice weevils or rice weevil-damaged grain. However, wasps that fed on rice weevils did not have a clear preference for rice weevils or wheat damaged by rice weevils. Likewise, field studies showed that wasps more effectively parasitized lesser grain borers when reared on lesser grain borers, but the same was not true for rice weevil. Nonetheless, wasps did feed on both stored product insect species and reduced feeding damage to wheat by 35-38% in lesser grain borer-infested wheat and by 1-18% in rice weevil-infested wheat. Overall, we found T. elegans effectively parasitized both stored product insect species in the field, but its preferences changed depending on which insect it was reared on. This suggests that careful attention should be paid to the insect species that is used for rearing this parasitoid for biocontrol releases.

Technical Abstract: Theocolax elegans (Hymenoptera: Pteromalidae) is a potential postharvest biocontrol agent whose host range includes Sitophilus oryzae (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae). Both host species are cosmopolitan and destructive pests of bulk wheat. In addition, either species could be used when mass rearing T. elegans. The Hopkins-Host Selection principle suggests the natal host environment may influence the semiochemicals an organism utilizes when foraging for oviposition sites. Thus, later efficacy may be impaired if important semiochemicals are lost from the foraging repertoire of T. elegans. In order to investigate the impact of natal host environment on the behavioral response of T. elegans to potential hosts, we reared T. elegans on either S. oryzae or R. dominica for multiple generations. We then we evaluated the orientation and taxis of T. elegans to six treatments: S. oryzae, R. dominica, damaged grain+S. oryzae, damaged grain+R. dominica, damaged grain+insects from the natal environment, or an undamaged control. We found T. elegans reared on R. dominica most preferred damaged grain from R. dominica in a four-way olfactometer, which was 4.2-fold more often chosen than S. oryzae individuals alone. Treatments containing R. dominica were differentiated from others based on headspace volatiles while S. oryzae-infested grain generally overlapped with uninfested grain. Both rearing host and subsequent foraging host affected efficacy of T. elegans released in a pilot-scale elevator. Wasps appeared most effective in suppressing grain damage by 35–38% when reared on R. dominica and foraging for R. dominica compared to S. oryzae-reared wasps that only reduced damage by 1–18%. Overall, we found that the natal host and chemical cues significantly affected taxis and foraging by T. elegans, suggesting that careful attention should be paid to the mass rearing procedure for this parasitoid.