Evaluating the biocontrol potential of lacewing larvae (Mallada basalis) against greenhouse thrips (Heliothrips haemorrhoidalis): predator functional responses to prey density at key life stages

Understanding predator-prey dynamics is crucial for assessing the biological control potential of generalist arthropod predators. The green lacewing (Mallada basalis) is a common natural predator in horticulture but has not yet been evaluated for its effects on greenhouse thrips (Heliothrips haemorrhoidalis) across different prey life stages. This study examined the functional responses of first and second instar M. basalis larvae to three life stages of thrips (second instar nymphs, pupae, and adults) under six initial prey densities (1, 2, 6, 10, 14, and 18 prey per cell) within a 24 h interval. The predation rate varied significantly (p < 0.05) overall with the instar of green lacewings and the life stage of thrips. Between the same prey densities, prey handling time of second instar lacewing larvae consistently exceeded (by c. 50%) that of first instar larvae. The quantity of prey that predators consumed appeared to vary with prey size, prey defence capabilities, and prey age. All functional responses were of type II but it shape varied at different prey developmental stages. Lacewing predation on pupal and adult thrips remained at low levels across varying densities, suggesting limited lacewing predation efficiency on these developmental stages. Our results indicate that lacewing larvae, particularly second instars, are effective predators of immature thrips and may contribute to biological control strategies targeting these early developmental stages. The stage-specific predation patterns we identified provide empirical insights for optimising the integration of lacewings into management programmes for greenhouse thrips.