Better alone than in bad company? Modeling the intra-guild predation and release timing in the biological control of Pseudococcus viburni

The obscure mealybug, Pseudococcus viburni, is a serious agricultural pest worldwide. The biological control in commercial fields of P. viburni relies on predators and parasitoids, in particular the generalist coccidophagous ladybird Cryptolaemus montrouzieri and the specific parasitoid Acerophagus flavidulus. However, these two natural enemies can establish an intraguild predation interaction, reducing the efficiency of biological control. Cryptolaemus montrouzieri may negatively impact the population dynamics of A. flavidulus if it feeds indifferently on healthy and parasitized mealybugs. With the aim of improving the biological control of P. viburni, in this work, we studied the feeding behavior of C. montrouzieri in the absence or presence of A. flavidulus larvae of different age within mealybugs, in laboratory conditions. Subsequently, with the data obtained, we mathematically modeled the dynamics of P. viburni to study the impact on P. viburni control of different field implementation schedules for the release of ladybird and parasitoid populations. The ladybird fed on parasitized P. viburni but reduced its consumption when they were infested by parasitoids aged of 4 days or more. Modeling results suggest that these feeding preferences of predators may have a positive impact on pest control, that releasing predators and parasitoids together is in general more effective than releasing them independently, and that releasing highly effective predators alone could be the best choice. Modeling results also provide information on different release schedules.