Acute and Sublethal Activity of the Entomopathogenic Fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) on Adult Aphelinus asychis (Hymenoptera: Aphelinidae)

In order to be most effective, components of integrated pest management programs should act in concert with minimal antagonistic interaction between natural enemy groups and other interventions. Entomopathogenic fungi and insect natural enemies have the potential to complement or interfere with one another, depending on environmental conditions. The acute and sublethal effects of the hyphomycete fungus, Paecilomyces fumosoroneus (Wize) Brown & Smith, on adult female Aphelinus asychis Walker, a common parasitoid of the Russian wheat aphid, Diuraphis noxia (Mordvilko), were studied under conditions of low (≈55% RH) and high (≥95% RH) humidity at 24°C. Parasites exposed to dosages of P. fumosoroseus ranging from 3.75 to 3.75 × 103 conidia per square centimeter and incubated at 24°C in low or high relative humidity responded with mortality ranges of 20-33% and 33-88%, respectively. The effect of treatment with P. fumosoroseus at 5.2 × 104 spores per square centimeter (2× LC95 for D. noxia) on foraging behavior of the parasitoid was studied with video image analysis 24-96 h after treatment with the fungus and incubation at low or high relative humidity. There was no significant difference between control and fungus-treated females that were incubated at the lower humidity in terms of percentage of time walking, turning, resting, and average walking speed. However, fungus-treated insects that were incubated at high relative humidity were significantly less active than their respective controls for percentage of time walking, walking speed, and distance covered. Also, average walking speed and distance walked by treated parasitoids incubated at low relative humidity for 96 h following treatment was significantly greater than treated insects incubated at the high relative humidity. Females treated with 2.6 × 104 spores per square centimeter and held in ≥95% RH for 24 h followed by incubation at 60% RH survived for an average of 5.7 d relative to 9 d for untreated females. The number of mummies produced per female per day was not significantly different between treated and untreated females, but more aphids were parasitized by the control insects due to longer survival. The limited untoward effect of P. fumosoroseus on adult A. asychis under conditions of lower humidity indicates good potential for their combined use for control of the Russian wheat aphid.