[Effects of low and subzero temperature on a Plutella xylostella laboratory population]

In this study, the effects of low (< 8 degrees C) and subzero temperature on the development, survival and reproduction of Plutella xylostella were examined. The mortality of its egg and pupae at 4 degrees C and 6 degrees C increased with time, no egg and pupae could complete their development at these low temperatures, and all died after 55 days and 70 days, respectively. When the pupae were placed at 4 degrees C and 6 degrees C for various durations and then moved to 16 degrees C for development, the fecundity of the resultant adults was reduced, and the longer the duration at 4 degrees C and 6 degrees C, the further the fecundity was reduced, and the fecundity was reduced to zero when the pupae were retained at these low temperatures for 45 days. The survival of this insect was observed following exposure of various stages of this insect to temperatures below 0 degree C. The results showed that the mortality of all preimaginal stages increased with decreased temperature and prolonged duration. The ability of cold tolerance of the various stages of this insect was in order of the third instar and pupa > the second and forth instars > the first instar and egg. Temporal exposure to temperatures below 0 degree C affected the development of subsequent stages at a favorable temperature. Generally, the developmental time of the subsequent stages increased, and the largest increase of development time was observed with the stage next to the stage treated at low temperatures. Exposure of the pupal stage to low temperature also reduced the fecundity of the resultant female adults, and the reduction was positively correlated to lower temperature and longer exposure.