Effects of temperature, soil humidity and soil cover on Plutella xylostella (Lepidoptera: Plutellidae) pupae emergence

Plutella xylostella is one of the main pests that affect vegetable commodity output. Current treatment by chemical pesticide spray has been considered the effective control of P. xylostella. This treatment has also developed the insecticide resistance, increased pesticide residue risks and threatened pollution-free vegetable production. In the present study, the effects of abio-chemical conditions such as temperature, soil moisture, water-logging and soil cover on P. xylostella pupae eclosion were investigated. The study aimed to elucidate agro-measure control effects, especially those of paddy/dryland rotation and soil plowing, on P. xylostella. The results showed that the rate of pupa emergence exceeded 73% at 26~30 ℃, which declined to 46.67% at 34 ℃. When treated at 4 ℃ and then grown at room temperature, the rate of pupae emergence dropped significantly. The longer the 4 ℃ pretreatment, the lower was the rate of pupae emergence. However, the emergency rate recovered to normal levels after long time of growth at room temperature. When soil moisture was 10% and 20%，the emergence rate was respectively 12.5% and 6.2% of that under normal moisture condition. No pupa emergence was observed within 6 d at soil moisture of 30%. When treated with water-logging for 12 h and 24 h and then returned to surface soil, the rate of emergence of P. xylostella pupae dropped respectively by 25.0% and 50.0% and emergency was delayed too. No pupa emergence was observed under extended treatment time of 36 h. Soil covering also had noticeable effects on P. xylostella pupa emergence. The emergence of pupae was delayed by 2 d when covered at 1 cm depth soil. Pupa did not successfully emerge when soil cover was 1.5 cm deep. The above results suggested that timely irrigation, paddy/dryland rotation and soil plowing were critical control factors of P. xylostella pupae in vegetable fields.