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Title: Biology and feeding requirements larval hunter flies Coenosia attenuata (Diptera:Muscidae) reared in larvae of the fungus gnat Bradysia impatiens (Diptera:Sciaridae)

Author
item Ugine, Todd
item SENSENBACH, EMILY - Cornell University
item SANDERSON, JOHN - CORNELL UNIVERSITY
item Wraight, Stephen

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2010
Publication Date: 8/2/2010
Citation: Ugine, T.A., Sensenback, E.J., Sanderson, J.P., Wraight, S.P. 2010. Biology and feeding requirements larval hunter flies Coenosia attenuata (Diptera:Muscidae) reared in larvae of the fungus gnat Bradysia impatiens (Diptera:Sciaridae). Journal of Economic Entomology. 103(4):1149-1158.

Interpretive Summary: The hunter fly Coenosia attenuata is native to southern Europe, but its range has expanded worldwide to include North America. Throughout its range, this generalist predator has become established in greenhouses and is considered beneficial, as it attacks many common greenhouse pests, including fungus gnats, shore flies, and leaf mining flies. Both the adult flies and the soil-inhabiting larvae are predatory. A few studies have investigated the biology of these insects, but much remains unknown, especially with regard to the immature stages. The objectives of this study were to determine the minimum and optimum numbers of three sizes (instars) of fungus gnat larvae (Bradysia impatiens) required by C. attenuata larvae to complete development to the adult stage. Results indicated a threshold number of between 10–15 small (second-instar) prey and 5–7 intermediate sized (third-instar) prey/day for successful development. Hunter fly larvae fed large (4th-instar) fungus gnat larvae were able to complete development when provided a single larva/day, but suffered high mortality (75%) from wounds received from defensive strikes by the prey. Prey succumbed very rapidly to attack, and we hypothesize mortality would be much lower in the natural soil habitat, where movements of tunneling prey would be restricted. The hunter fly larvae killed large numbers of prey during their development (average 232 2nd instars, 144 3rd instars and 87 4th instars when prey were abundant) and fed actively for 12–14 days. These findings are useful in assessing the biological control potential of the larval stage of this predator, and will contribute toward development of methods or strategies to enhance activity of these beneficial insects in the greenhouse environment.

Technical Abstract: The larval feeding requirements and biology of the generalist predatory muscid fly Coenosia attenuata were investigated at 25 deg C. Larval C. attenuata were fed 2nd-, 3rd-, and 4th-instar (L2, L3, and L4) larvae of the fungus gnat Bradysia impatiens at variable rates to determine minimum and optimum numbers of these prey required for normal development. The proportion of C. attenuata larvae surviving to pupation differed significantly as a function of L2 and L3 prey numbers. When the number of prey/day was increased from 10 to 15 L2 and from 5 to 7 L3 per day, the respective percentages of pupation increased from 0 to 77% and 0 to 48%. In contrast, all numbers of 4th-instar (L4) prey (1–7/day) supported pupation, and the pupation rate did not vary with prey number. At the highest prey numbers tested, mortalities of C. attenuata larvae fed L2, L3, and L4 fungus gnat larvae were 7, 30, and 75%, respectively. The higher mortality of larvae fed L4 prey was clearly the result of lethal wounds inflicted by the fungus gnat larvae in defensive strikes against the predators. At prey numbers supporting maximum rates of adult emergence, larval development required 12–14 days, and duration of the pupal stage was ca. 10 days. C. attenuata larvae killed large numbers of prey during their development (means of up to 232 L2, 144 L3, or 87 L4 fungus gnats), and larvae provided with marginally inadequate numbers of prey survived for long periods (mean 14–22 days, maximum 34 days) before succumbing to apparent starvation. These are favorable attributes with respect to use of C. attenuata as a biological control agent, suggesting a strong potential to substantially impact high-density pest populations and to survive in low-density pest populations.