Insecticide resistance in Plutella xylostella (Linnaeus) (Yponomeutidae) in the Federal District, Brazil: effects of local and long-range movement of moths

Abstract

In this study the level of insecticide susceptibility of Diamondback Moth strains from the Federal District, located in the central region of Brazil, was evaluated in 1995 and in 1996. A large degree of homogeneity in deltamethrin, acephate and
phenthoate susceptibility was observed in the surveyed strains. One strain, highly susceptible to B. thuringiensis in August 1996, lost its susceptibility after approximately two generations in the field with a 36- fold increase in its LC_50• Movements of the pest were suggested as one factor that could account for the observed results.
The intensity of selection for resistance Diamondback Moth by insecticides applied to cabbages was studied by examining the distribution of larvae on the plants in relation to the penetration of the spray and the distribution of residues.
It was concluded that for insecticides with no translaminar activity, a proportion of the larvae are likely to remain protected from exposure. Insecticide resistance management strategies are discussed taking into account the results obtained, with special emphasis on the insecticide chlorfluazuron.
Diamondback Moth males were caught in pheromone traps deployed in an area that was at least 12 km away from the nearest brassica fields, which confirmed that movements of the pest over at least this distance occurred. The occurrence of local movements of moths was also confirmed using pheromone traps in sprayed and unsprayed areas of brassica cultivation. A light trap deployed in a field showed sudden increases in the numbers of adults that could not be explained by local emergence. Two types of Diamondback Moth movements could have occurred: a) long-range migratory movements or b) local population redistribution. Although the relative importance of these different types of movements remains to be determined, it is pointed out that immigrating Diamondback Moth can carry genes for insecticide resistance and may be responsible for spreading resistance into new areas.

Date of Award	Sept 1997
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) Amazônia Oriental
Supervisor	Alexander Gatehouse (Supervisor)