Study on Biological Characteristics of Polyphylla gracicornis

Polyphylla gracicornis generate 1 generation in 4 years and live through the winter by larva. The larva living through the winter start to damage the forest in early April every year and live through the winter in late October. Its activity range is 10～25 cm in soil and the soil depth in which it live through the winter is 40～70 cm. Its imago generate in middle June and dominant period is in middle and late July; the dominant hatching period of larva is in early and middle August. The duration of pupa is 29 days, ovum is 26 days, larva with 1 instar is 340 days, larva period with 2 instars is 365 days, larva period with 3 instars is 700 days and imago period is 16 days. The ratio of female and male imago is 1.2:1, and they are active in the day and keep quiet at night and the active peak time is 21:00～23:00. The imago is free from food. The female imago oviposit sporadically and they average amount of ovum are 26, mainly oviposit in the soil with depth of 15cm. The land with deep soil, appropriate water and rich nutrient is subject to damages of these insects.