Cold hardiness of the red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) in Shanghai

The invasive red palm weevil (RPW), Rhynchophorus ferrugineus (Olivier), native to Southern Asia, is becoming a serious invasive pest of palms in China. In order to understand how well the RPW survives under cold temperature, with materials from fields in Shanghai we determined the supercooling points (SCPs) with supercooling point determinator and the degree of cold hardiness in environmental chamber at low temperatures, simulated field overwintering test in Shanghai, and analyzed the north limit for overwintering of RPW. The results indicated that SCPs of the RPW were significantly decreased as the developmental stages increased. Adults had the lowest SCPs, followed by 9th, 5th and 1st instar larvae and eggs in an increasing order. The viability of various developmental stages in the RPW was measured in 6, 24, 48 and 72 h, and the relationship between the survival rate and low temperature could be fitted with logistic model significantly or extremely significantly. Ltemp50(the temperature that results in 50% mortality of the experimental population) was increased as time prolonged at all stages of the RPW. At 72 h after treatment, Ltemp50 values of eggs, 1st instar larvae, 5th instar larvae, 9th instar larvae and adults were 1. 61, -1.67, -2.39, -2.40 and -0.40[degree]C, respectively. This result showed that the larvae had the highest cold hardiness, followed by adults and eggs in order. The above data indicated that the correlation between the cold hardiness and SCPs was not uniformly positive. Thus, we speculated that either adult or larva could be possible stage of overwintering for the RPW. The field ovenvintering test also showed that survival rates of both larvae and adults were above 60% in continuous two years ( 2007 and 2008), suggesting that the RPW could overwinter in the field in Shanghai. Based on the results obtained and distribution of the hosts of the RPW, we tentatively inferred that the northern limit for overwintering of the RPW is proximate to 35[degree]N or where the average low temperature in January is around 0[degree]C.