Mellitobia acasta (Hymenoptera: Eulophidae) female longevity and life stage-dependent parasitism using commercially managed Megachile rotundata (Hymenoptera: Megachilidae) as hosts

Authors: ANDERSON, ALAN - Utah State University; RAMIREZ, RICARDO - Utah State University; CREECH, J - Utah State University; Pitts Singer, Theresa

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2023
Publication Date: 5/31/2023
Citation: Anderson, A.R., Ramirez, R.A., Creech, J.E., Pitts Singer, T. 2023. Mellitobia acasta (Hymenoptera: Eulophidae) female longevity and life stage-dependent parasitism using commercially managed Megachile rotundata (Hymenoptera: Megachilidae) as hosts. Journal of Insect Science. 23(3). Article 5. https://doi.org/10.1093/jisesa/iead031.
DOI: https://doi.org/10.1093/jisesa/iead031

Interpretive Summary: Melittobia acasta is one among other parasitoid wasps that is a pest of the alfalfa leafcutting bee, Megachile rotundata, which is the primary, commercial pollinator for North American alfalfa seed production. This wasp has a very high rate of reproduction when using the leafcutting bee as a host and can reduce or destroy bee stocks. Hundreds of M. acasta female offspring can develop in a single host cell and leave that cell to infest others to produce thousands more parasitoid wasps. In this study, we determined 1) the bee life stages upon which M. acasta females will lay eggs and if those eggs produce adults and 2) M. acasta female longevity when exposed to various resources within bee cells. We found that M. acasta females lay eggs on mature bee larvae (prepupae) and pupae that survive to adulthood. Eggs are not laid on early instar bee larvae; eggs laid on adults do not survive. Average female life span is five days without feeding, eight days if the bee larva’s pollen-nectar provision is available while the bee develops though larval stages, and 34 days if the wasp can feed on prepupal “blood” (hemolymph). According to our results, wasp females can emerge from bee cells several days after trays of cells are taken to fields. Therefore, just-emerged females could survive long enough for new bee offspring to become prepupae. Our findings support a better understanding of host preference and longevity of M. acasta females that can inform when to use possible control measures.

Technical Abstract: Melittobia acasta Walker is one among other hymenopterous parasitoids of Megachile rotundata F. Commercial M. rotundata populations are employed to pollinate North American alfalfa for seed production. This wasp can be prolific when using M. rotundata as a host and can reduce or destroy bee stocks. Hundreds of M. acasta female offspring can develop in a single M. rotundata cell and disperse to infest other cells, producing thousands of more parasitoids. In this study, we determined (i) upon what bee life stages M. acasta females choose to lay eggs and if those eggs ultimately become adults and (ii) M. acasta female longevity when exposed to various resources within M. rotundata cells. We found that M. acasta females lay eggs on M. rotundata prepupae and pupae and that those eggs can hatch and survive to adulthood. Eggs are not laid on early instar bee larvae; eggs laid on adults do not survive. Average female life span is 5 days without feeding, 8–9 days if a pollen–nectar provision is available while the bee develops through larval stages, and 34 days if the wasp can feed on prepupal hemolymph. Wasp females can emerge from bee cells several days after trays of cells are taken to fields. Therefore, adult females could survive long enough for new bee offspring to become prepupae. Our findings support a better understanding of host life stage preference and the longevity of M. acasta females that can inform the timing of the implementation of possible control measures.