Assessment of interspecific interactions among parasitoids on the outcome of inoculative biological control of leafminers attacking chrysanthemum

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 pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of existing 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 in a simulated, field cage grown, cut chrysanthemum 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. 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. Treatment comparisons included single species releases with complimentary releases of both species either simultaneously or with 2-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 (low densities), and thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively or positively affect the outcome of the augmentative biological control, nor was there a positive outcome; however, crop quality at harvest was influenced.