UC Riverside

Resource provisioning as a habitat manipulation tactic to control the melon aphid, Aphis gossypii, by the polyphagous aphid parasitoid, Aphidius colemani, was investigated in the ornamental, potted-plant nursery using the shrub Photinia x fraseri as a plant host. Floral food resources from an invasive, Conium maculatum, an ornamental, P. x fraseri, and a native, Salvia apiana considerably improved the longevity and fecundity of A. colemani in laboratory experiments. Additionally, floral nectar from P. x fraseri and honeydew from A. gossypii had a statistically similar effect on the longevity, fecundity, percent emergence, and sex ratio of A. colemani and enhanced the parasitoid more than extrafloral nectar from Cucurbita pepo. In common garden field studies, A. colemani remained for the entire seven days tested in the presences of resources while in the absence of resources, the parasitoid was detected for only 3 days. Further field studies using floral food of P. x fraseri, honeydew of A. gossypii, and a flowers x aphids treatment were conducted to determine the effects on the abundance and movement of the parasitoid in a common garden. Significantly more parasitoids were initially associated with flowers x aphids treatment 24 h post release. This was followed by a switch to the aphids treatment 1 week later. Parasitoids were found in both the treatment plots and associated crop plots (no resources) suggesting that A. colemani moves in search of resources and may be switch-foraging to maximize fitness.

Imidacloprid, a systemic insecticide commonly used in nursery systems, was detected in the xylem, nectar, pollen, and leaves of P. x fraseri treated with a full or half label rate. The concentration of imidacloprid detected in the xylem and nectar was greater than the determined LC₅₀, LC₇₅, and LC₉₀ of imidacloprid for A. colemani. Bioassay data suggested the survival of the parasitoid is negatively impacted by feeding on nectar from imidacloprid treated plants. No effect was observed when the parasitoid was exposed to leaves from imidacloprid treated plants. These findings suggest that soil-applied imidacloprid is moderately compatible with biological control due to toxicity occurring through contact with nectar from treated plants rather than direct exposure.