Studies On The Factors Affecting Egg Hatch And Larval Development Of Bactrocera Minax

The Chinese citrus fruit fly,Bactrocera minax,is one of the most destructive pest of citrus.They are a serious threat to citrus production and international trade.There is a bottleneck in conducting basic research with this fly because their eggs and young larva cannot be successfully reared in lab.This study focused on studying the effects of different gut symbiotic bacteria on the fitness and survival of the eggs and larvae of B.Minax.In addition,we also emulated the conditions in the wild to promote the development of eggs and larvae in the laboratory.This was carried out by varying the temperature,nutrition and propionic acid content and studying their effects on egg hatch and larva development.The main results were as follows:1.Comparing the citrus composition in healthy and damaged fruitsThe sugar,acid and nitrogen content were measured in healthy citrus fruits and infested fruits of different varieties.As a healthy fruit develops,the total acid content increases and then decreases while their sugar content gradually increases.Our results showed that,the total sugar content of infested fruits containing eggs were higher than that of uninfested fruits.Contrarily infested fruits containing larvae had a total sugar content lower than that of uninfested fruits.The nitrogen content of infested fruit containing eggs and first instar larvae was not significantly different from uninfested fruits.However,infested fruits containing second and third instar larvae,had a significantly higher nitrogen content.Understanding the conditions under which the eggs and young larvae develops in citrus fruits in the wild provides the bases for improving their domestication2.Isolation and identification of bacteria from larval guts and infested fruitsUsing physiological,biochemical and 16S rDNA-ARDRA analysis,a total of 8different bacteria specie were isolated from the oviposition site on the fruit,they were Corynebacterium glutamicum,Escherichia hermannii,Kosakonia cowanii,Staphylococcus capitis,Enterobacter sp.,Pantoea agglomerans,Enterobacter cloacae,Kosakonia sp.In addition,5 different species were isolated from the part of the fruit where the first instar larvae hatched,these included Bacillus megaterium,Enterococcus gallinarum,Lysinibacillus sphaericus,Bacillus subtilis,Pantoea agglomerans.In addition,5 and 3 bacteria were isolated from the first and third instar larva respectively,they were Bacillus licheniformis,Escherichia fergusonii,Staphylococcus hominis and Providencia rettgeri,Bacillus licheniformis,Staphylococcus capitis,Providencia sp.,Providencia sneebia respectively.This study lays the foundation for further work to be carried out on the impact of resident bacteria on the fitness of the Chinese citrus fly.3.Effects of symbiotic bacteria on B.minax fecundity,egg hatch and larva survivalThe results showed Citrobacter freundii significantly increased the longevity of B.minax adults,the average mating frequency and female fecundity,and Lactococcus garvieae significantly increased the longevity of the female fly.Pantoea agglomerans on the other hand,significantly increased the average mating frequency and female fecundity.Finally,Enterococcus faecalis and Enterobacter cloacae significantly increased fecundity.After adding Lactococcus garvieae and Enterobacter cloacae to Q diet,the survival rate of newly hatched larvae from 18% to 49% and 42%,respectively.On the other hand,adding Lactococcus garvieae and Enterobacter cloacae to B diet,recorded a survival rate from 49% to 62% and 60%,respectively.4.Effects of environmental factors on egg hatch and larval development of B.minaxA shorter developmental time of 25 days was recorded when eggs were treated with different concentrations of propionic acid at a pH of 3.0.These treatments had a hatch rate of 43%.The rate of egg development was relatively fast when diunal temperatures were varied.However,temperature variations did not affect developmental rates.The survival rate of the second instar larvae reared at 25 was the highest compa℃ red with the other temperatures.Larvae reared at a temperature of 23 ℃had the highest pupation rate.The survival rate of newly hatched larvae was increased from 18% to 49%after adding cholesterol and glucose or sucrose and adjusting the pH to 3.4,The survival rate of the second instar larvae reared on A and B diets increased from 67% to 97% and100% and their pupation rate increased from 39% to 87% and 97% respectively.This study has brought to the lamp light the bacteria associated with the eggs and the young larvae of the Chinese citrus fly which may play a role in their development and survival.Furthermore,the effects of gut bacteria isolates and other abiotic factors on adult fecundity,development and survival of newly hatched larvae were also studied.The present study lays the foundation for improving on the domestication of the Chinese citrus fly,a crucial tool necessary for research and development of sustainable techniques necessary for the management of this fly.