| Litchi is a featured fruit which holds a significant economic value in Guangdong,China.The most harmful pest in litchi production is Conopomorpha sinensis Bradley,whose larvae bore into the host,seriously affecting the yield and quality of litchi.At present,farmers mainly adopt chemical pesticides to prevent and control infestations,leading to the problem of "pesticide residue",which seriously impedes the export of litchi.Responding to the government’s call for high-quality agricultural development,new environmentally friendly and safe prevention and control strategies must be explored to replace the chemical pesticides.Previous research has identified that fallen litchi fruits as an important source of C.sinensis,thus,removing fallen fruits is a significant approach.Besides,exploring the overwintering mechanism of C.sinensis is an important prerequisite for winter pest control.This study aims to evaluate the effect of removing fallen fruits as a prevention and control method for C.sinensis.The prevention and control effect of the treatment area(regularly removed fallen fruits)was evaluated by investigating and comparing boring rate for fallen fruit,pupation quantity of 100 fallen fruits,adult quantity of 100 fallen fruits,quantity of adults on tree and fruiting rate of egg-bearing in the treatment area and the control area period-by-period.Secondly,in order to examined the development of C.sinensis in low temperature conditions and the cold resistance of each insect states,explore the overwintering insect state,therefore,the egg period and hatching rate,pupal period and eclosion rate,male and female adult life span and supercooling point of C.sinensis were detected at 10℃,13℃,15℃,17℃,20℃ and 26℃,respectively.In final,adult populations were monitored throughout the year to gain further insights into C.sinensis dynamics after fruit harvesting.The main conclusions are as follows:1.The average rate of bored fallen fruits in May in the control area reached 60%,and there were a maximum of 41 pupae and a maximum of 21 adults in 100 fallen fruits,respectively,indicating that fallen litchi fruits are an important source of insects.Larvae continually came out from the collection of fallen fruits within11 days and formed pupae,indicating that the condition and nutrition of fallen litchi fruits can maintain the normal development of C.sinensis throughout the entire larval stage.2.The rate of fruits bored in the treatment area was significantly lower than the control area on 23 May,however,there was no significant difference between control and treatment areas in the rest of the time.When compared with the control area,the average reduction in the number of pupae was36.59%,the average reduction in the number of adults on the tree was 50.23%,and the average reduction in the number of egg-bearing fruits was 60.53% for the C.sinensis insects in the treatment area.It is shown that insect boring in the young fruit stage is one of the main causes for litchi fruits dropping,removing fallen fruits can effectively reduce the density of C.sinensis,improve litchi fruit-bearing rate,reduce the fruit boring rate,and thus improve yield and quality.3.The eggs could not hatch when the temperature below 13℃,the hatching rate was 40% to 44% between 15℃ and 20℃,the hatching rate was 66% at 26℃.The pupae could not emergence below 10℃;the eclosion rate was 10% at 13℃,the eclosion rate was 30% to 38% between 15℃ and 17℃,the eclosion rate was 70% to 80% between20℃ and 26℃.Both the period of egg and pupal stages increased significantly as the temperature decreased.The average winter temperature in Guangzhou City is 13℃ to16℃,indicating that the C.sinensis eggs cannot live through the winter,and some pupae can live through the winter.4.The life span of male and female adults at 15°C was 124.68 ± 8.42 d and 105.60± 7.07 d,respectively,which was significantly higher than that at other temperatures.When the temperature is 10℃ to 26℃,the effects of different temperatures and different refrigerating time on the supercooling point of female adults were low.The supercooling point of male adults increased with the increase of refrigerating time at26℃,and the supercooling point was not affected by different refrigerating time at 13℃to 20℃,and decreased with the increase of refrigerating time at 10℃.Compared with the adults captured in the field,the supercooling point of male and female adults treated with different temperatures was increased,with variations ranging from 0 to 6°C.It shows that the C.sinensis are freezing tolerant insects with poor supercooling ability;most adults can live through the winter in Guangzhou.5.In mixed orchards of litchi and longan,C.sinensis adults will migrate between litchi and longan trees depending on the degree of preference for the hosts.The number of adults feeding on fruits far exceeded the number feeding on shoots.The number of population was 0 in December to February when the temperature was low.This suggests that temperature and nutrients are the main reasons of changes in the population dynamics of the C.sinensis.This study clarifies that the cleaning of fallen fruits is one of the effective measures to prevent and control the C.sinensis,which provides a new direction for the prevention and control of the C.sinensis.Preliminary exploration of the development of each insect state in low temperature conditions and their cold resistance,providing theoretical support for the study of overwintering mechanism of C.sinensis. |
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