Testing method of pesticide on Grapholitha molesta (Busck) neonate larvae

YU Qin; FENG Yuntao; GUO Xiaojun; DU Enqiang; GUO Guiming; ZHANG Runxiang

doi:10.13925/j.cnki.gsxb.20170066

Abstract：[Objective] Grapholitha molesta is a destructive pest of many fruits.Although difficult,chemical pesticide spray is still the most common way to control the pests.There are serious problems in the current testing methods which are aimed at the adults and eggs,for instance,more dosage and longer times are needed to effectively control the pests.We had proved that G.molesta neonate larvae were more sensitive to chemical pesticides than the adults and eggs.Neonate larvae should be one of the key methods of chemical control.But currently there is no toxicity testing method to measure the efficiency to G.molesta neonate larvae because of the high mortality of neonate larvae crawling and gnawing on apples after hours.This paper aims to study a way to measure the pesticide efficiency with fewer errors.[Methods] In order to study the control efficiency determination method of pesticide to G.molesta neonate larvae,the survival rate and damage rate of G.molesta neonate larvae was measured by using different developmental states of the pests and the apple fruit.The pests included ready-to-hatch eggs and neonate larvae,the apples included fruitlet (d=3.5-4.0 cm),ripening fruit (d≥7.0 cm) and cut-ripening fruit.The neonate larvae and larvae were fed in a artificial intelligence incubator with (25±1) ℃,3 000-4 000 lx light,D∶ L=15 ∶ 9.The number of eggs laid on the apples was 13 or 14 eggs per fruitlet,40 eggs per ripening fruit or 20 eggs per cut-ripening fruit.The number of neonate larvae laid on the apples was 10 neonate larvae per fruitlet,15 neonate larvae per ripening fruit or 30 neonate larvae per cut-ripening fruit.The survival rate was surveyed in 14 h after laying the eggs or 8 h after laying the neonate larvae.The damage rate was surveyed 5 d after laying the eggs or neonate larvae.Damage symptoms and the growing development of the G.molesta was observed with an Olympus stereoscope in 10 h,14 h,18 h,30 h,54 h,78 h and 5 d.The survey method was determined by carefully observing pest morphological characteristics and damage symptoms of G.molesta on apples and the damage rate at different times.The pesticides included λ-Cyhalothrin and Chlorantraniliprole.96.0％ λ-Cyhalothrin and 95.3％ Chlorantraniliprole were dissolved in propanone and 5 different series concentrations were diluted with water.That was done as follows:washing and drying apples were dipped into a solution for 5 min,pulled out and the solution was removed with filter paper,then laying eggs or neonate larvae were applied.The borers were investigated in 30,54,78 h and 5 d.The number of borers was the same as the number of holes 30 h and the number of borers was the same as the number of traces at 54 h and 78 h.Experimental data were analyzed with Duncan's new multiple range test statistical methods.[Results]The survival rate of G.molesta neonate larvae was ＞ 90％ and its damage rate was 76.81％-77.18％ using ready-to-hatch eggs and apple fruitlets.The borer rate was 76.80％,77.18％ laid eggs on fruitlets and cut-ripening fruit and greater than 62.60％ laid eggs on ripening fruit.The borer rate dropped to 65.56％,53.32％ and 56.68％ from 76.80％,62.60％ and 77.18％ when G.molesta neonate larvae was laid on the fruitlets,cut-ripening fruit and ripening fruit,respectively.The control efficacy of λ-cyhalothrin to G.molesta neonate larvae using cut-ripening fruit was higher than ripening fruit and fruitlets.The control efficiency of 3.00 and 4.00 mg· L-1 λ-cyhalothrin to G.molesta were 21.88％,22.38％,26.04％ and 31.25％,31.33％,35.42％ for the laid eggs on fruitlets,cut-ripening fruit and ripening fruit respectively,and there were no significant differences among similar concentrations.The control efficiency of 5.00 and above λ-cyhalothrin to G.molesta were 48.98％-98.96％ on cut-ripening fruit which was higher than the 38.80％-97.01％ on fruitlets and ripening fruit.Damage symptoms of G.molesta larvae changed constantly with prolongation of time after laying ready-to-hatch eggs on the apples.The number of traces of endangered pests was the same as the number of living G.molesta larvae in 54 h and 78 h after laying ready-to-hatch eggs on the apples.G.molesta larvae was affirmed as dead after showing no action after being touched or not moving freely in 14 h after laying ready-to-hatch eggs on the apples or in 8 h after laying neonate larvae on the apples.The damage rate was investigated in 30 h and 54 h after ready-to-hatch eggs laid on apple based damage symptoms.The holes which had adhering frass and no traces of endangered pests in 54 h and 78 h after laying ready-to-hatch eggs on the apples could not be counted as borers.G.molesta larvae still died even if bored into the apples,particularly in pesticide treatments.The G.molesta larvae could continue to damage and grow when the individuals lived in 54 h after laying ready-to-hatch eggs on the apples.The control efficiency of 3.33 and 5.00 mg· L-1 λ-cyhalothrin to G.molesta were 19.19％ and 33.33％ in 30 h and were significantly lower than 23.96％ and 40.63％ in 54 h and after.So 54 h after laying ready-to-hatch eggs on the apples is reasonable surveying time of the toxicity test for G.molesta neonate larvae.The control effect of Chlorantraniliprole to G.molesta neonate larvae increased with the increase of the concentrations using the above methods and measured parameters.Its corresponding linear equation was y=2.148 4x+ 1.367 8,R2 was 0.937 1.[Conclusion] Using the methods of immersion fruitlets and inoculation ready-to-hatch eggs,the survival rate of the controlled processing was no less than 90％ and its damage rate was no less than 70％,the number of borers were determined according to pest damage symptoms.The above methods and parameters could test the control efficiency of G.molesta neonate larvae.It needs to be validated whether this control efficiency method was appropriate for measuring the toxicity test of G.molesta neonate larvae.