Consumption of Susceptible and Bt-Resistant Spodoptera frugiperda Eggs by Ladybeetles and Lacewings: Preference and Functional Responses

Immature ladybeetles and lacewings can thrive by feeding on eggs of lepidopteran pests, such as Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). However, considering that the survival and fitness performances of generalist predators are heavily dependent on their ability to select suitable prey, we first evaluated whether eggs of S. frugiperda strains with differential susceptibilities to Bacillus thurigiensis (Bt) toxins would affect the food preference of larvae of the ladybeetle Coleomegilla maculata DeGeer (Coleptera: Coccinellidae) and the lacewing Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae). We further determined, for the first time, the functional responses of all immature phases of both predator species when fed with S. frugiperda eggs. In our choice bioassays, predator larvae were individually offered 25 eggs of each S. frugiperda strain. The number of consumed eggs was recorded hourly and replenished during each evaluation. For the functional responses, increasing densities of S. frugiperda eggs were offered to the larvae of lacewings and ladybeetles, and the number of consumed eggs was recorded 24 h after the release of the predator. Ch. externa larvae had a generalized preference for Bt-susceptible strains of eggs, while Co. maculata exhibited such a ,preference only during the first evaluation hour. Both predators displayed type II functional responses, and their consumption substantially increased during larval development. By demonstrating that lacewing and ladybeetle larvae can satisfactorily consume S. frugiperda eggs, including eggs from Bt-resistant individuals, our findings reinforce the potential of these predatory insects for the ecological management of S. frugiperda.