| The Red Palm Weevil Rynchophorus ferrugineus(Olivier)(RPW), a borer insect which causes destructive damage to the palm trees, has been documented as one kind of forestry quarantine pests in China and an international quarantine pest in the world.We determined the Supercooling point (SCP) of egg, early-stage larvae (ES larvae), middle-stage larvae (MS larvae), old-stage larvae (OS larvae), pupae, female adult and male adult of RPW, counted the corrected mortality of the above subjects exposed to variedly low temperature with different time, and exploited the effect of different cold-acclimation on the physiological mechanism for old larvae as well as effect of fluctuant temperature condition on chill-injury for adults. Results showed as followed:1. There’s significant difference of SCP among our subjects (P<0.05), SCP of egg could reach as lowest as any other stages with the mean value of-26.19±0.28℃for early-stage egg and-24.04±0.28℃for old stage egg, then followed by ES larvae (-17.02±1.53℃), female adult (-11.86±0.28℃), pupae (-11.40±0.29℃), male adult (-10.87±0.87℃), MS larvae (-10.34±0.38℃) and OS larvae (-8.73±0.28℃) with the highest one. Frequency distributions of SCP of all developmental stages followed the normal distribution except for egg stages.2. Corrected mortality interacted with exposure temperature and exposure time for all developmental stages of RPW; The Ltimeso and Ltempso of subjects increased with the exposure temperature raised and the exposure time prolonged; Ltimeso of egg, ES larvae, MS larvae, OS larvae, female adult and male adult exposed to0℃were:0.823h、5.422h、10.311h、6.464h、12.127h、11.326h, therefore, we concluded that0℃should be the lethal temperature for RPW in Hainan and the cold hardness of our subjects sorted by different developmental stages should be:female adult>male adult>MS larvae>OS larvae>ES larvae>egg.3. The content of antifreeze protein induced from hemolymph for OS larvae declined with the cooling rates decreased. The highest content of antifreeze protein induced from hemolymph for OS larvae was26.89mg/ml with the cooling rate at1℃/min, almost4to5times than that of control group, while the lowest one was9.08mg/ml with cooling rate at0.05℃/min; The content of glycerol, total sugar, total lipid and total protein from hemolymph of treatment group were higher than that of control group, while the total water content of treatment group was significant lower than that of control group (P<0.05).From the relationship between corrected mortality and changes of physiological indictors of OS larvae exposed to different cooling condition. we clarify the main cold-resistant system for OS larvae exposed to low temperature within short period should be antifreeze protein induced from hemolymph; Meanwhile, the effective cooling rates for OS larvae for cold-acclimation should be a range between1℃/min to0.1℃/min.4. Effect of fluctuant temperature exposure and constant temperature exposure on chill injury of RPW adult is different. Fluctuation of lethal temperature would counteract some degrees of chill injury for both female and male adult, thus increased their cold hardness, for example, the Ltimeso of female and male exposure to fluctuant temperature at0℃were27.42h and21.71h, which were significantly higher than that of constant exposure at0℃(12.13h and11.33h). However, fluctuation of milder temperature would accelerate the speed of chill injury for both female and male adult, thus decreased their cold hardness, for example, the Ltimeso of female and male exposed to fluctuant temperature at15℃were387.44h and296.11h, which were significantly lower than that of constant exposure at15℃(850.56h and659.8h)(P<0.05). |
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