Dispersal of adult western flower thrips (Thysanoptera: Thripidae) on chrysanthemum plants:: Impact of feeding-induced, senescence of inflorescences

The currant study investigated the interaction among density, feeding impact, and dispersal of western flower thrips, Frankliniella occidentalis (Pergande), on potted flowering chrysanthemum plants. In cage experiments using chrysanthemum plants infested with either 0, 400, 800, or 1,200 thrips, the proportion of senescent inflorescences increased with time and with the number of thrips released on chrysanthemum plants. Positive correlations between the proportion of senescent inflorescences and the density of thrips per inflorescence for different time periods indicate that the feeding activity of thrips causes a premature senescence of inflorescences. On plants infested with 0 or 400 thrips, population density slightly increased for 10-14 d and then leveled off; on plants infested with 800 or 1,200 thrips, in contrast, population density remained high for 7-10 d and then steadily declined to very low levels. A high proportion of senescent inflorescences was positively correlated with the proportion of females that dispersed on blue sticky cards for different time periods, whereas the rate of dispersal by males was not consistently impacted by the quality of inflorescences. Releasing adult thrips marked with fluorescent powder in greenhouses indicated that the quality of inflorescences meditates the dispersal behavior of adult thrips up to a distance of 4 m: females are more likely to disperse from senescent than healthy inflorescences and preferentially colonize healthy inflorescences over senescent inflorescences. The dispersal behavior of adult thrips has important implications in terms of sex-specific optimal reproductive strategies, sampling procedures, and population dynamics.