Abstract
When two or more parasitoid species, particularly candidates for biocontrol, share the same target in the same temporal window, a complex of behaviors can occur among them. We studied the type of interactions (competition and intraguild predation) that existed between the nymphal parasitoids Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae), two candidate neoclassical biocontrol agents against the Puerto Rican cactus pest mealybug, Hypogeococcus sp. (Hemiptera: Pseudococcidae). The surrogate native congener host in Argentina, the cactus mealybug Hypogeococcus sp., was studied to predict which species should be released; in the case that both should be released, in which order, and their potential impact on host suppression. In the laboratory we conducted experiments where different densities of the host mealybug were exposed to naive females of A. cachamai and A. lapachosus sequentially in both directions. Experiments were analyzed by combining a series of competitive behavioral and functional response models. A fully Bayesian approach was used to select the best explaining models and calculate their parameters. Intraguild predation existed between A. cachamai, the species that had the greatest ability to exploit the resource, and A. lapachosus, the strongest species in the interference competition. The role that intraguild predation played in suppression of Hypogeococcus sp. indicated that a multiple release strategy for the two biocontrol agents would produce better control than a single release; as for the release order, A. lapachosus should be released first.
Highlights
Intraguild predation is a combination of exploitative competition and predation among potential competitors that use the same host or prey[1,2], either a uni- or bidirectional interaction
The first theoretical models developed on intraguild predation analyzed the changes that occurred in the equilibrium of the populations of the intraguild predator, the intraguild prey, and in the resource shared by both, as a function of the environmental productivity[12,13,14,15,16,17]
Laboratory studies were carried out with colonies of the parasitoid species A. cachamai and A. lapachosus reared at Fundación para el Estudio de Especies Invasivas (FuEDEI) facilities since 2014 with the methodology described in Aguirre et al.[28]
Summary
Intraguild predation is a combination of exploitative competition and predation among potential competitors that use the same host or prey[1,2], either a uni- or bidirectional interaction. The first theoretical models developed on intraguild predation analyzed the changes that occurred in the equilibrium of the populations of the intraguild predator, the intraguild prey, and in the resource shared by both (i.e., the pest), as a function of the environmental productivity[12,13,14,15,16,17] According to these models, if the intraguild predator is a weaker resource competitor (inferior natural enemy) than the intraguild prey, both can coexist, or even exclude the intraguild prey. One of the most common difficulties of these kinds of experiments is to elucidate what happens inside the h ost[24] and the effect of host availability on the ability of the wasps to locate the h osts[25] To solve this problem, Bruzzone et al.[26] proposed a novel approach that integrates competitive behavioral and functional response models. The models developed allow the description of the competition process of endoparasitoids both on interference (which species is a better interference competitor, if the competitor has advantages by arriving first; and when arriving second, whether the parasitoid avoids, accepts, or prefers the already parasitized hosts), and exploitation (if there are differences in terms of functional response)
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