Adaptability To Environmental Temperature Of Invasive Insect Pest Wallacea Dactyliferae On The Palmaes

Wallacea dactyliferae has been reported as a new invasive palm pest recently.It originated in southern India and then spread to Bangladesh,Vietnam,Thailand and Yunnan and Taiwan of China.It invaded and colonized in France in 2004.W.dactyliferae has a certain ability to invade a new environment,and may further spread the danger in China in the future.For most insects,temperature is an important factor constrains their population distribution and spread range.Therefore,this study focuses on the optimum temperature range of W.dactyliferae and the tolerance of W.dactyliferae to extreme temperature.These two scientific questions are of great practical and theoretical value to answer the adaptability of W.dactyliferae to different environmental temperatures,to promote the population prediction and prevention of W.dactyliferae and to understand the adaptability mechanism of insect to temperature.The main results are as follows:1.The W.dactyliferae belongs to order Coleoptera,superfamily Chrysomeloidea,family Chrysomelidae,subfamily Cassidinae,tribe Botryonopini.The main feature of the adult is that its mouthpart is relatively close to the place where the antennae are inserted and not separated by the large labial base.At the base of the antennae,4 segments are submoniliform,reddish brown,and covered with sparse pubescent hairs.The segments 5-11 are linear,black,wide and long,and densely covered with pubescent hairs.2.The developmental duration,reproductive capacity,survival rate and other population parameters of W.dactyliferae under different constant temperatures were compared using the age-stage,two-sex life table.The population dynamics of each developmental stage of W.dactyliferae within 600 days were also predicted for evaluation.The results showed that the intrinsic growth rates were 0.0070,0.0227,0.0376,and-0.0028 at 15,20,25,and 30℃,respectively,and the net reproductive rates were 16.8,100.4,69.5 and 0.8,respectively.Therefore,temperature above 30℃is not conducive to the population growth of W.dactyliferae;the optimum temperature for reproduction was 20℃;the optimum temperature for population growth was 25℃.3.The tolerance limit of W.dactyliferae adults to extreme high temperature was defined.Under extreme high temperature stress of 0.5 h to 4 h,the high lethal temperature of HLT₅₀0 was 37.4⁴0.7℃.Within a short period of time（0.5 h）,it can only withstand the high temperature below 39℃,however,it is not capable of bearing the high temperature for a long time.4.The tolerance of extreme low temperature in W.dactyliferae adults as well as the cold tolerance strategies were clarified.The supercooling point of W.dactyliferae adult was-17.6℃.However,the low lethal temperature of LLT₅₀0 of W.dactyliferae was-4.9^-9.6℃.It was concluded that adults of the W.dactyliferae were all dead already when the internal ice was formed.The cold tolerance strategy of the adults should be chill-susceptible type with a weak cold resistance under the condition of constant temperature rearing at 25℃and the adults do not have the ability to withstand the low temperature for a long time.5.After rapid cold hardening with different intensities,the cold tolerance of adult W.dactyliferae was significantly improved,and the survival rate increased from 22.2%to 60.0¹00%under-9℃/2 h stress.At the same time,after rapid cold hardening,the supercooling point of W.dactyliferae decreased from-17.6℃to-20.9^-28.3℃;the water content of the body decreased from 64.2%to 48.3%;the content of glycerol and trehalose of the body increased to 84.0%and 100%respectively,while the glycogen content of the body did not differ significantly among different cold hardening treatments except a significant decrease by21.8%only at 0℃.In summary,the optimum temperature of W.dactyliferae is 25℃.W.dactyliferae is not tolerant to extreme temperatures while has a certain plasticity in cold resistance.It can rapidly enhance cold tolerance through rapid cold hardening,indicating that it may have a great potential to migrate to northern China and threaten the palm plants.The results of this study provide a theoretical basis for further understanding the adaptability of W.dactyliferae to environmental temperature and predicting its potential distribution area.