Residual toxicity of insecticides to Chrysoperla rufilabris and Rhyzobius lophanthae predators as biocontrol agents of pine needle scale
2020
Quesada, C.R. | Sadof, C.S.
Determining toxicity of insecticides to natural enemies is essential for integrated pest management (IPM) programs of armored scales. In our previous work, insecticides did not affect seasonal abundance of parasitoids and predators of scale insects when they were applied one-month before their peak of season activity. In contrast, when applied during periods of natural enemy activity, trees treated with the broad-spectrum insecticide bifenthrin had fewer parasitoids and predators than trees treated with horticultural oil or the reduced risk insecticides pyriproxyfen, spiromesifen, and spirotetramat. In the current study we determined whether, bifenthrin, and the other insecticides differed in residual toxicity to two common predators, Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae) and Rhyzobius lophanthae Blaisdell (Coleoptera: Coccinellidae). First we developed a bioassay that provided predators adequate resources to survive our eight day bioassay. Then, field-grown pine trees were infested with pine needle scale, Chionaspis pinifoliae (Fitch) (Hemiptera: Diaspididae), and treated with insecticides. Pine needles were collected for use in a bioassay that exposed C. rufilabris and R. lophanthae to insecticide residues of different ages. All insecticide treatments reduced live pine needle scales compared to an untreated control. Residues of bifenthrin were slightly toxic to R. lophanthae adult 21 DAT (days after treatment) but were harmless to C. rufilabris larvae 14 DAT. In contrast, horticultural oil and pyriproxyfen, spiromesifen, and spirotetramat did not kill C. rufilabris or R. lophanthae 1 DAT. Our data showed that reduced-risk insecticides can kill pine needle scale and have less residual toxicity than the broad-spectrum insecticide bifenthrin on both C. rufilabris and R. lophanthae.
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