Comparative Studies On Cold Hardiness And Instar Determination Of Eucryptorrhynchus Scrobiculatus And E.brandti

Eucryptorrhynchus scrobiculatus Motschulsky and its relative E.brandti(Harold)are major pests of Ailanthus altissima(Mill.)Swingle and A.altissima var.Qiantouchun.These two weevils are host specific,and they are widely distributed in China.E.scrobiculatus and E.brandti caused severe damage to forests in Ningxia Hui Autonomous Region.The two weevils have been listed in "national forestry pests" published by The State Forestry Administration in 2003 and 2013,respectively.Low temperatures in winter have direct effects on the overwintering survival,growth,reproduction and spread of insects.Seasonal changes of ambient temperature may affect the supercooling capability and the synthesis of biochemical substances of overwintering insects.In this paper,researches published have been reviewed and some key factors of cold hardiness had been observed and proper experiments were designed to figure them out.Furthermore,larval instars of E.scrobiculatus and E.brandti have been determined.All the research results are as followsSeasonal changes in supercooling point and freezing point of E.scrobiculatus.For both adults and larvae,the change tendency of supercooling point and freezing point were positively correlated with the environment temperature,which reached the lowest in January.In July and September,supercooling point and freezing point were significantly higher compared to the over-wintering stage,which showed that the supercooling point can reflect the individual’s cold-resistant ability.The supercooling point and freezing point of adult in each period were below the larvae,which showed that adults’ cold-resistant ability was stronger.Seasonal changes in supercooling point and freezing point of E.brandti.The supercooling point and freezing point of both adults and larvae showed significant differences in different seasons,which tended to decrease initially before increasing,and the values were consistent with the seasonal changes in the ambient temperature.The seasonal changes of supercooling point and freezing point of larvae were identical with the adults.Cold-resistant ability of E.brandti was increased with the decreasing of external temperature,adults’ cold-resistant ability was significantly stronger than larvae.Seasonal changes in percentage water content and lipid content of E.scrobiculatus.Variation trends of percentage water content and lipid content of E.scrobiculatus were identical with the seasonal changes.Cold-resistant ability had grown with the values of percentage water content and lipid content tended to decrease.Seasonal changes in percentage water content and lipid content of E.brandti.Water content of both adults and larvae was significantly lower in the middle of the overwintering period(January)compared with that in the late overwintering period and summer(March and July).Water content of E.brandti were positively correlated with the environment temperature,and presents certain hysteresis.The changes in lipid content tended to decreased at first and then increased,and differed significantly in over-wintering stage.Determination of larval instars of E.scrobiculatus and E.brandti.Larval samples of various sizes were collected from both the field and the laboratory and measured different morphological variables.Based on the results of a frequency distribution method and Dyar’s rule,the larvae of E.scrobiculatus and E.brandti were divided into seven instars.The width of the head capsule provided the best measurement for determining instar stage.