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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Pest Management and Biocontrol Research » Research » Publications at this Location » Publication #205844
Title: Susceptibility of immature stages of Homalodisca coagulata (Hemiptera: Cicadellidae) to selected insecticides

Author
item PRABHAKER, NILIMA - UNIV CA, RIVERSIDE, CA
item Castle, Steven
item TOSCANO, NICK - UNIV CA, RIVERSIDE, CA

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2006
Publication Date: 12/1/2006
Citation: Prabhaker, N., Castle, S.J., Toscano, N.C. 2006. Susceptibility of immature stages of Homalodisca coagulata (Hemiptera: Cicadellidae) to selected insecticides. Journal of Economic Entomology 99:1805-1812.

Interpretive Summary: Effective chemical control requires knowledge of how particular insecticides act against target pest populations. Different developmental stages of a pest insect often vary widely in susceptibility to insecticides. Applications in the field can potentially be adjusted to target a predominant stage occurring at the time of treatment. The glassy-winged sharpshooter (Homalodisca coagulata) is a good candidate for selective targeting with insecticides due to its discrete generations in southern California citrus that tend to produce large numbers of nymphs, but very few adults, during spring. The present study examined the toxicities of various insecticides to each nymphal stage and revealed that mortality declines with each successive instar. All insecticides tested proved highly toxic to GWSS nymphs with the highest toxicities produced by the neonicotinoid acetamiprid and the pyrethroid bifenthrin.

Technical Abstract: Susceptibility of immatures of the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), to 10 insecticides that included chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam was evaluated in the laboratory. All five instars were exposed to different doses of each foliar insecticide by the petri dish technique, whereas a systemic uptake method was used to assess the toxicity to imidacloprid and thiamethoxam. All test insecticides exhibited high toxicity to all immature stages of H. coagulata at concentrations below the field recommended rates of each insecticide. Although all five instars were susceptible to test insecticides, mortality was significantly higher in first instars than in the older immatures based on low LC50 values (ranging from 0.017 to 5.75 ng(AI)/ml) with susceptibility decreasing with each successive stage. Fifth instars were generally the least sensitive (LC50 values ranging from 0.325 to 216.63 ng(AI)/ml). These results show that mortality was directly related to age of the insect and suggest that chemical treatment at early stages is more effective than at late stages. Acetamiprid (neonicotinoid) and bifenthrin (pyrethroid) were the most toxic to all five instars, inducing most mortality within 24 h and showing lower LC50 values ranging from 0.017 to 0.686 ng/ml compared with other insecticides (LC50 values ranging from 0.191 to 216.63 ng(AI)/ ml). Our data suggest that a diverse group of very effective insecticides are available to growers for controlling all stages of H. coagulata. Knowledge on toxicity of select insecticides to H. coagulata immatures may contribute to our understanding of resistance management in future for this pest by targeting specific life stages instead of the adult stage alone.