LARVAL BIOLOGY AND CONTROL OF THE RABBITBRUSH BEETLE, TRIRHABDA-NITIDICOLLIS LECONTE (COLEOPTERA, CHRYSOMELIDAE)

The chrysomelid, Trirhabda nitidicollis LeConte, is a common defoliator of rabbitbrush, Chrysothamnus spp., in rangeland areas throughout much of western North America. With the expanded use of this plant in ornamental settings, T. nitidicollis has developed further economic importance, and studies were conducted to better understand its biology and to evaluate control methodology. In the area around Laporte, Colorado, first-instar larvae were first observed on 17 April 1991 and 7 April 1992. Peak larval populations occured during May and adults were present from late May through early September. Eggs were laid as small masses in soil, and there were three instars with mean head capsule diameters of 0.55 mm, 0.89 mm and 1.39 mm for first through third instar, respectively. Three species of predaceous stinkbugs (Hemiptera: Pentatomidae) were observed feeding on T. nitidicollis larvae and adults, including Perillus bioculatus (Fabr.), P. exaptus (Say), and Apateticus bracteatus (Fitch). In addition, larvae were fed upon by the coccinellid, Hippodamia quinquesignata (Kirby). Biological insecticides containing the active toxin of Bacillus thuringiensis var. tenebrionis (M-One, M-Trak) and carbaryl gave excellent control of larvae.