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Species guide - species detail

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Melittobia acasta (tiny parasitic wasps)



Melittobia acasta are tiny, parasitic wasps in the family Eulophidae. M. acasta is a type of wasp that parasitizes different Megachile species, particularly M. rotundata. When M. acasta uses M. rotundata as a host, it can reproduce rapidly and potentially harm bee populations. This is an issue because M. rotundata is commonly commercially used to pollinate alfalfa crops. This wasp can lay hundreds of offspring in a single cell of M. rotundata which then spreads to infest other cells, leading to the production of thousands more parasitoids.


Melittobia acasta are extremely small parasitic wasps with an average length of only 1mm-1.5mm. When looking at the facial features of M. acasta, the species has narrow facial grooves that run separately to the facial scrobes and do not converge mid-face. The scape and the pedicel of the antennae in M. acasta is darkly and uniformly colored throughout. The costal margin of the forewing is almost entirely straight and does not diverge at an angle as in other species. These specimens can be hard to identify to species as they tend to deflate and shrivel when air-dried and have microscopic differences/characteristics.

Nest Structure

Melittobia acasta infiltrates the nests of Hymenoptera, Coleoptera, Diptera, Lepidoptera, and Blattodea. In our case, they are solely infesting the nests of Hymenoptera, most commonly different Megachile species. The wasps lay their eggs on the prepupae and pupae of bee species. When the eggs hatch, the wasp larvae consume the prepupae or pupae. Since M. acasta is a very fertile species that can lay hundreds of eggs in multiple generations, bee cells can easily become overwhelmed with these parasites.

Hole Sizes

No information at this time.


In Minnesota, Melittobia acasta is particularly prolific and can produce many generations with its multivoltine cycle.

Activity Period

Melittobia acasta is active in Minnesota from mid-May to September.


Anderson, A. R., Ramirez, R. A., Earl Creech, J., & Pitts-Singer, T. L. 2023. Melittobia 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): 5. Dahms, E.C. 1984. Revision of the genus Melittobia (Chalcidoidea: Eulophidae) with the description of seven new species. Journal of Entomology 10(2): 123-136.

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.

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