| Abstract: In order to explore the overwintering ability of Plutella xylostella in Yan'an area undernatural conditions, the supercooling points, low temperature viability and overwintering outdoors undernatural conditions of Plutella xylostella were studied. The results indicated that for Plutella xylostellalarvae, the supercooling point of the first instar larvae was the lowest, which was -17.07 ℃. The averagesupercooling point of larvae was -14.36 ℃, following by -15.25 ℃ in adults and the lowest supercoolingpoint was observed in pupae, which was -19.45 ℃. These results showed that the cold tolerance of pupaewas the strongest in various stages. Under 5, 0, -5 and -10 ℃ conditions, Plutella xylostella pupae's LT50,LT90 and LT99.9 were shortened as the temperature decreased. The time required for the 99.9% pupae's deathwas 52.82, 29.03, 26.17, 13.45 d, respectively. This indicated that Plutella xylostella could not survivein the area where winter temperature was below 0 ℃ for more than 29 d. In addition, the results of fieldoverwintering experiment showed that the Plutella xylostella pupae's overwintering mortality was 100% inYan'an. Combined with winter temperature change rules of Yan'an area, it was preliminarily concluded that Plutella xylostella could not pass the winter under natural conditions in Yan'an. |