Impact of interspecific interactions among parasitoids on inoculative biological control of leafminers attacking chrysanthemum



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Texas A&M University


Indigenous natural enemies occur within field grown crops at varying densities dependent upon a variety of other biotic and abiotic parameters. This natural control often does not provide adequate suppression, which results in the application of other remedial pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of indigenous natural enemy populations, competitive interactions are likely to occur. To assess the influence of these interspecific interactions on the outcome of such biological control practices, studies were conducted both in a laboratory and in a simulated, field grown, cut chrysanthemum (Asteraceae: Dendranthema grandiflorum) production system. Competitive interactions of two commercially available parasitoids were studied both in terms of parasitoid-host population dynamics and the impact of interspecific interactions on crop quality at harvest in this type of system. The parasitoids Diglyphus isaea and Dacnusa sibirica attacking the leafminer Liriomyza langei were used as the model insect system. Both parasitoids are cosmopolitan and are known to occur in many ornamental production areas. Conclusions drawn from laboratory experiments were that D. sibirica produces more offspring that D. isaea over approximately the same number of days. Treatment comparisons in the field included single species releases with complimentary releases of both species either simultaneously or with two-week time lags, as well as a no release control to measure the background effects of natural mortality. Conclusions drawn from results of population-level studies replicated within and among years were that levels of interspecific competition among parasitoid species were undetectable at leafminer densities typical of field-grown ornamental crops; thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively affect the outcome of the augmentative biological control. The two species were able to coexist inside field cages for the duration of the crop. Most of the release treatments suppressed host densities lower than the control cages where no parasitoids were released, and there were no treatment effects on host suppression. Even though parasitoid release combination did affect the amount of damage visible at harvest, there was no influence on the number of flowers produced (yield).