| Camellia weevil, Curculio chinensis is a highly specialized insect of oil-tea Camellia, a unique woody oil crops in China. The lavae develop inside the fruits and cause a lot of fruit drop before harvesting. The weevil’s serious infestation has become a bottleneck for the healthy development of oil-tea industry, since it’s very difficult to control. At present, the studies on the camellia weevil focused on damage surveys, and the systematic and further research on the biology and ecology has rarely been involved.In this article, it was researched about the influence of fruit traits on damage degree of camellia weevil and the adaption strategies of the weevil to variation of fruit traits from the perspective of co-evolution between insects and plants. Fallen drop before harvesting and fruits infested by weevils were collected randomly, and the fruit traits were measured, then the number of juveniles (eggs and larvae) was counted, frequency distribution method of the head capsule width was used to determine the larval instars. The results were as follows:1.191larvae of camellia weevil in different developmental stages were collected at Yiyang region, Hunan province in2013, and their head capsule widths, mandible widths and lengths were measured by means of a binocular microscope coupled with an micrometer (to the nearest0.01mm). Frequency distribution method and Dyar’s rule were used to determine the larval instar number and larval instars, and Crosby law and linear regression analysis were used to choose the optimal morphological index for determining the larval instars of camellia weevil. The results indicated that there were5instars for camellia weevil, instead of4instars reported before. The head capsule width provided the best index to divide instars, since its mean coefficient of variation and Crosby ratio were the least. The linear regression equation of natural logarithm of the head capsule width against the instar number was:y=0.4055x+5.5646, R2=0.997. The growth of the head capsule increased geometrically with a mean growth ratio of1.502, and it followed the Dyar’s rule. 2. To understand the key pre-harvesting factors affecting fruit drop and the relationships between camellia weevil and fruit traits of Camellia meiocarpa, fallen fruits were collected randomly with the parallel sampling method, weight, height and diameter of the fallen fruits were measured, then the correlation analysis between camellia weevil and fruit traits of C. meiocarpa was conducted. The result was showed as follows:Glomerella cingulata and camellia weevil were the main factors affecting fruit drop, and infestation of pests would obviously affact the development of the fruits. Camellia weevil infestation rate was negatively correlated with fruit size, and it presented parabola change with the fruit shape index increasing, and had a maximum value of27.10%when the fruit shape index reached1.04±0.03, but there was no relationship between camellia weevil infestation rate and pericarp thickness of C. meiocarpa.3. Fruits infested by camellia weevil were collected randomly with the parallel sampling method before (July8) and after (July30) the peek of oviposition of weevil adults, and weight, length and diameter of the infested fruits were measured, then each fruit was dissected and the number of juveniles (eggs and larvae) was counted. Linear regression was used to analysis the correlations among puncture number, clutch size, weevil infestation rate and fruit weight, polynomial curve fitting was used to assess the relationships among puncture number, clutch size, weevil infestation rate and fruit shape index. The results was showed as follows:Puncture number, clutch size and weevil infestation rate were positively correlated with fruit weight before the seed coats of C. meiocarpa have been hardened, but there was no correlation among clutch size, weevil infestation rate and fruit weight after the seed coats have been hardened. The weevil infestation rate gradually decreased with the fruit shape index deviating from the value1.0, and it presented parabola change with the fruit shape index increasing. The result tested that the camellia weevil would prefer bigger and spherical fruits to lay eggs, and supported the "optimal foraging theory". |
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