EFFECTS OF SUBLETHAL COLD STRESS ON THE WESTERN FLOWER THRIPS, FRANKLINIELLA-OCCIDENTALIS

In order to establish in a new geographical area, introduced insects m ust be able to survive any period of adverse conditions such as a temp erate winter and be capable of subsequent development to adulthood and /or reproduction. However, this aspect of insect overwintering and col d tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshou ses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of t ime during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult fe male Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non-stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though co ld treated larvae took approximately two days longer to reach adulthoo d than untreated individuals (at 20 degrees C, 18L:6D). Chill treatmen t of adult females significantly reduced their rate of reproduction (f rom 1.45 to 0.93 larvae day(-1)), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10. 8 larvae), compared to control females. Acute exposure resulted in non -significant decreases of the same parameters. The relevance of the ab ove effects to overwintering of F. occidentalis is discussed.