Temperature-dependent fecundity of overwintered Unaspis yanonensis (Hemiptera: Diaspididae) and use of degree-days for the prediction of first crawler

Abstract

The longevity and fecundity of the overwintered arrowhead scale, Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae), was examined at constant temperatures. The total fecundity increased up to 24 °C and declined thereafter. Total fecundity reached a maximum of 260.9 eggs per female at 24 °C. Females demonstrated periodic oviposition activity but the pattern differed with temperature. The first cycle of fecundity was not significantly different between 16 and 28 °C. However, fecundity in the latter cycles, measured at rearing temperatures of 16, 20 and 32 °C, was lower than at 24 and 28 °C. The pre-oviposition period ranged from 49.0 d at 16 °C to 19.7 d at 32 °C, and was shortest (19.4 d) at 28 °C. The longevity was found to be greatest (87.3 d) at 16 °C and was as short as 48.9 d at 32 °C. Regression of the mean development rate vs. temperature provided a low-threshold temperature estimate of 8.7 °C for the pre-oviposition stage and a thermal constant of 358.4 degree days. The theoretical low threshold temperature and thermal constant applied to the calculation for the completion of the U. yanonensis pre-oviposition period predicted the appearance of first crawlers in the field.