Abstract
Maternal effects of heat shock are reported for some species of insects, but little is known about such effects in the western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). WFT is a pest of vegetables in greenhouses worldwide. It is susceptible to high temperatures in its natural environment and is controlled using heat treatment in China. WFT population growth is suppressed by a brief exposure to a high temperature of 40°C or 45°C in the laboratory. To explore the mechanism by which high temperatures suppress the growth of WFT populations, as well as the effects of multiple heat treatments on WFT, we recorded the duration of development and survival of immature WFT, and the sex ratio (female/male) and fecundity of F1, F2, F3 and F4 adult females that developed after a single heat shock, and those of F2 offspring after a double heat shock. We also recorded the longevity and ovarian structure of adult females of the treated generation (P) and their F1, F2 and F3 offspring after a single heat shock. In addition, we determined whether the effects of a heat shock on second instar nymphs and adults differed. The results indicate that exposure of the parental generation to 41°C or 45°C for 2 h significantly prolonged the duration of development, reduced survival of immature WFT and altered the sex ratio (female/male), longevity and fertility of their adult female offspring. The effects of a heat shock of 41°C persisted for two generations, whilst the effect of heat shock of 45°C persisted for three generations. In addition, double heat shocks had more pronounced effects than a single heat shock. Heat shock administered to second instar nymphs resulted in a decrease in the number of ovarioles, whilst a heat shock administered to adults resulted in ovariole deformity. The maternal effects of heat shock in terms of the biological parameters of WFT, structure and number of ovarioles, are critical in determining the suppression of the growth at high temperatures of WFT populations.
Highlights
Maternal effects of environmental factors are reported for plants (Roach & Wulff, 1987) and insects (Crill et al, 1996; Chen et al, 2011)
We investigated the effects of subjecting the parents to a heat shock on the duration of development and survival of the immatures, the sex ratio and the fecundity of adult females of the first (F1), second (F2), third (F3) and fourth (F4) generation offspring, and the longevity and structures of the ovaries of the females in the treated generation (P) and their F, F and
Similar trends were recorded in the experiments in which the heat shock was applied to second instar nymphs of the parental generation; the thermal injury caused by 45°C was more pronounced than that caused by 41°C, and the effects of 45°C persisted for more generations than that of 41°C (Fig. 2)
Summary
Maternal effects of environmental factors are reported for plants (Roach & Wulff, 1987) and insects (Crill et al, 1996; Chen et al, 2011). WFT are native to North America and have spread to nearly 70 countries on all continents except Antarctica (Van Rijna et al, 1995) This insect pest has caused severe damage to vegetables in greenhouses in Beijing, China since 2003 (Zhang et al, 2003) and has recently spread to Shandong Province (Zheng et al, 2007). This pest is susceptible to high temperatures in its natural environment and is controlled using heat treatment in China. The results of this study may improve our understanding of the mechanism by which high temperatures suppress the growth of WFT populations
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