Effect of temperature on the development of Laodelphax striatellus (Homoptera: Delphacidae).

Temperature has a significant influence on the development of Laodelphax striatellus (Fallén), an important rice pest insect in east Asia. We set eight constant temperatures from 18 to 32 degrees C in 2 degrees C-increments to check the effect of temperature on the developmental rate of this insect species. The developmental durations of eggs and nymphs were observed daily. To ensure the accuracy of developmental durations, 500 initial samples were taken for the nymphal stage at each temperature. Performance-2 model was used to fit these data because this model can provide the lower and upper developmental thresholds simultaneously. The estimate of lower developmental thresholds of eggs (10.0 degrees C) was different from that of nymphs (7.5 degrees C). And the estimate of upper developmental thresholds of eggs (35.5 degrees C) was also different from that of nymphs (30.2 degrees C). However, for male and female nymphs, the difference in the lower developmental threshold is nonsignificant, and the difference in the upper developmental thresholds is very small (95% confidence interval of the difference: [0.007 degrees C, 0.043 degrees C]). The rate isomorphy hypothesis considers that the lower developmental thresholds of different stages for the same insect might be constant. However, the current study provides a counterexample of this hypothesis that the lower developmental threshold of eggs is different from that of nymphs. Thus, we demonstrate that the rate isomorphy hypothesis does not apply all insects. In addition, we used a popular nonlinear model, Lactin model, to fit the developmental rate data of our experiment. And we found that the estimates of lower and upper developmental thresholds by using Performance-2 model were very approximate to those by using Lactin model. The current study provides reliable estimates of thermal parameters for L. striatellus by using large experimental samples at different temperatures. It would be useful for exploring the relationship of climate change and the outbreak of this insect on rice.