Laboratory biology and field population dynamics of Trichopria columbiana (Hymenoptera: Diapriidae), an acquired parasitoid of two hydrilla biological control agents

Abstract

The biology and population dynamics of Trichopria columbiana, a native semi-aquatic parasitoid of ephydrid flies of the genus Hydrellia, were investigated in Florida and Texas, USA. Hydrellia pakistanae and Hydrellia balciunasi were introduced for classical biological control of the invasive aquatic weed Hydrilla verticillata in the 1980s and acquired T. columbiana post-release. Several life history parameters of T. columbiana were investigated in the laboratory, including fecundity, egg shape and size, number and location of egg(s) deposited per host, preferred host age, description and number of instars, mode of respiration and host-selection behaviour. Field studies included seasonal abundance of T. columbiana and the introduced Hydrellia spp., parasitism levels, overwintering stage and adult winter sex ratio. T. columbiana is a synovigenic solitary endoparasitoid that developed from egg to adult in 21.9 ± 0.2 days under laboratory conditions. Eggs of T. columbiana are hydropic, hymenopteriform in shape and possess a double membrane. Larvae have three instars; first instars have sclerotised mandibles, bifurcated abdominal appendages and are free floating in the host’s haemolymph. Second and third instars are grub-like and remain attached to the host’s tracheal system until pupation. Individual females produced on average 23.2 ± 0.6 eggs and survived 15.6 ± 1.8 days. Highest parasitism levels of early and intermediate stage pupae occurred when wasps were 8–9 days old. Field parasitism rates of the two introduced Hydrellia spp. averaged 19.1%.

Keywords:

• Hydrellia pakistanae
• Hydrellia balciunasi
• Hydrilla verticillata
• weed biocontrol
• parasitoid accumulation
• apparent competition

Acknowledgements

We thank the following individuals for their technical contributions to this research, in particular, Jerry Butler, Judy Gillmore, Pam Howell, Pauline Lawrence, Michelle Leonard, Karen McKenzie, Julie Nachtrieb, James Nation, Linda Nelson, Christi Snell and Robin Swindle. The authors also thank Lubomir Masner for identification of T. columbiana as well as for comments on the ecology of the wasp, and Howard Frank and Bill Overholt for reviewing an earlier draft of this manuscript.

Funding

This work was funded in part by a US Department of Agriculture, Agricultural Research Service/Institute of Food and Agricultural Sciences, University of Florida Cooperative Agreement [No. 58-6629-4-008]; the US Army Engineer Aquatic Plant Control Research Program.

Additional information

Funding

Funding: This work was funded in part by a US Department of Agriculture, Agricultural Research Service/Institute of Food and Agricultural Sciences, University of Florida Cooperative Agreement [No. 58-6629-4-008]; the US Army Engineer Aquatic Plant Control Research Program.