Pesticide Susceptibility of Cybocephalus nipponicus and Rhyzobius lophanthae (Coleoptera: Cybocephalidae, Coccinellidae)

Trevor Randall Smith, Ronald D. Cave


The susceptibility of the predatory beetles Cybocephalus nipponicus Endrödy-Younga and Rhyzobius lophanthae Blaisdell to 6 pesticides commonly used for treating cycad aulacaspis scale, Aulacaspis yasumatsui Takagi, was tested. Three concentrations (half field rate, field rate, and twice field rate) of each pesticide were tested against both beetle species with a coated glass vial bioassay. Nearly 100% mortality in both beetle species occurred at all concentrations when treated with methidathion, dimethoate, and malathion. Insecticidal soap, fish oils, and imidacloprid were much less toxic. At one-half the field rate, C. nipponicus had 66% mortality with insecticidal soap, 76% mortality with imidacloprid, and 83% mortality with fish oil. At one-half the field rate, R. lophanthae had 43% mortality with insecticidal soap, 63% mortality with imidacloprid, and 46% mortality with fish oil. Mortality rate for each beetle species rose with increasing concentration of each pesticide and the soap and oil were the least toxic of all pesticides tested.

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