COMPARATIVE OPTIMAL TIMES OF APPLICATION OF BENZOYLPHENYL UREAS TO WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE)

Abstract

AbstractFour benzoylphenyl ureas (BPU’S) were tested on the four feeding larval instars of western spruce budworm, Choristoneura occidentalis Freeman, from a nondiapausing laboratory colony. BPU’s compared were chlorfluazuron, penfluron, triflumuron, and XRD-473 (N-(((3,5-dichloro-4-(1,1,2,2-tetrafluoroethoxy)phenyl-amino)carbonyl)-2, 6-difluorobenzymide). Although previous evidence suggested that BPU’S were generally most active on younger instars, last-instar western spruce budworm larvae were most susceptible to three of the four tested. Contour plots of estimated effectiveness during development of a western spruce budworm laboratory population indicated that the optimal time of application (lowest LC90) for XRD-473 would be ca. 16 days after the first group of larvae hatched, but the optimal time for the other three BPU’s would be between 40 and 50 days after hatch began. However, chronological age of insects in natural populations is difficult to estimate because of the influence of factors such as climatic conditions (e.g. temperature) and other ecological factors. The need to estimate optimal timing for application of BPU’s and other chemicals in terms of physiological time during population development is discussed.