| Summary: | 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).
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