Topical Toxicity of Imidacloprid, Fipronil, and Seven Conventional Insecticides to the Adult Convergent Lady Beetle (Coleoptera: Coccinellidae) 1 Nawal Kaakeh 2 , Walid Kaakeh and Gary W. Bennett Center for Urban and Industrial Pest Management, Department of Entomology Purdue University West Lafayette, Indiana 47907-1158 U.S.A. J. Entomol. Sci. 31(3): 315-322 (July 1996) ABSTRACT The relative toxicities (comparing LD50 and LT5xtsqponmljihgfedcbaTSQ qs) of two synthetic pyrethroids (cypermethrin and fenvalerate), two organophosphorus insecticides (chlorpyrifos, diazinon), three carbamates (propoxur, carbaryl, bendiocarb), a phenylpyrazole representative (fipronil), and a heterocyclic nitromethylene representative (imidacloprid or NTN 33893) were assessed with topical bioassays in the laboratory against the convergent lady beetle, zyxwvutsrqpon Hippodamia convergens Guerin Meneville. LD5q values decreased (i.e., toxicity increased) with an increased time after application of a specific insecticide. The differences between the LD50 values caused by various insecticides were significant. Among tested insecticides, cypermethrin and bendiocarb were the most toxic; fipronil was the least toxic. H. convergens responded differently to different insecticides within the same class. Beetles exhibited similar responses to both organophosphorothionates chlorpyrifos and diazinon 24 to 72 h after application. Of the carbamates, propoxur was 2.4 and 3.5 times less toxic than carbaryl and bendiocarb, respectively. Of the pyrethroids tested, cypermethrin was significantly more toxic than fenvalerate. At 800 ppm, cypermethrin and bendiocarb were the fastest in killing H. convergens among the tested insecticides. The ranking of insecticides in decreasing order of LT50 values was as follows: fipronil > diazinon > chlorpyrifos > propoxur > carbaryl > fenvalerate and imidacloprid. KEY WORDS Hippodamia convergens, predator, topical toxicity The convergent lady beetle, Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae), is an important cosmopolitan natural enemy species in many agricultural settings (Hagan 1962). The application of most insecticides produced a greater loss of beneficial arthropods than any other agricultural practice (van den Bosch 1966). From the standpoint of possible integrated chemical and biological control programs utilizing H. convergens, it is preferable to use insecticides that are less toxic to these predators. Most available 1 Received 03 October 1995; Accepted for Publication 02 June 1996. 2 Current address: Department of Plant Protection, College of Agriculture, Aleppo University, Aleppo, Syria 315 Downloaded from http://meridian.allenpress.com/jes/article-pdf/31/3/315/1561905/0749-8004-31_3_315.pdf by guest on 19 October 2023