Effects of Temperature and Photoperiod on Reproduction of the Rice Black Bug, Scotinophara coarctata (Fabricious)

Abstract

The rice black bug, Scotinophara coarctata, was recorded as an occasional pest
but has now become a potential major pest of rice in Thailand. This study investigates
the influence of temperature and photoperiod on reproduction of S. coarctata.
Newly-hatched first instar nymphs were reared in a constant conditions at 25, 30 and
35°C in 10:14, 11:13, 12:12 and 13:11 LD. The findings suggest that temperature is
the dominating factor on nymphal development of S. coarctata. The study finds that
more than 50 percent of fertile mating pairsare found both at 25 and 30°C. Thus,
here isno reproductive diapause in S. coarctata under constant conditions. However,
the number of surviving adults significantly decreased when kept at 30°C and no
nymphs survived at 35°C, so the selected rearing temperatures for investigating the
effect of changing photoperiod on reproduction of S. coarctata is 25°C. To determine
how reproduction of S. Coarctata is affected by photoperiod, first instar nymphs were
reared under both constant (10:14 and 13:11 LD) and induced-changing photoperiod
conditions. In the latter case, first instar nymphs were pre-maintained at 25°C in a short
day (10:14 LD) and long day (13:11 LD) conditions. Until the third instar, nymphs
were transferred into the opposite photoperiod conditions from short to long day and
long to short day conditions. The results show that the fecundity of S. coarctata reared
at 25°C under changing photoperiod conditions are not significantly affected when
photoperiod was changed. The critical information derived from this study indicates
that temperature is the dominating factor on reproduction and there is no reproductive
diapause occurring under either constant or induced-changing photoperiod conditions.