Regional outbreaks of diamondback moth due to movement of contaminated plants and favourable climatic conditions.

Outbreaks of diamondback moth, Plutella xylostella (L.), are being documented more frequently in many regions of the world and the causes for the outbreaks are often associated with insecticide resistance and lack of natural enemies, the latter often due to use of broad-spectrum insecticides. Growers are likely to think of insect management on an individual field basis (i.e. their fields) without sufficient regard to the larger context in which the insect operates on a regional basis, and this may limit their ability to manage the pest. Like any insect, P. xylostella populations fluctuate on an intra-regional and inter-regional basis and outbreaks in either case may be due to many factors. In this paper two causes of specific outbreaks of P. xylostella, movement of contaminated plants and an unusual climate within a region, are discussed.