Synergistic Control Of Drosophila Melanogaster By Entomogenous Fungi And Plant Essential Oils And Their Pathogenicit

Drosophila melanogaster that belongs to a genus of fruit flies in the family Drosophila of the order Diptera,is a borer pest.At present,the control of D.melanogaster mainly relies on chemical agents,but since D.melanogaster infests mostly berries,its planting and fruiting period is strictly controlled by all kinds of chemical agents,therefore,its effective and safe control is an urgent problem at present.Entomopathogenic fungi are an important biopesticide with the advantages of high efficiency,low toxicity,no pollution and environmental friendliness,which has become a hot spot for research.In this study,we used entomopathogenic fungi and D.melanogaster as research objects.Through the initial screening of highly virulent strains and indoor virulence determination,we screened out the insecticidal fungal strains with high virulence against adult D.melanogaster.The pathogenic mechanism of entomopathogenic fungi was studied by scanning electron microscopy.Nine kinds of toxic plant essential oils were selected to screen out the plant essential oils with good compatibility with highly virulent strains,and the synergistic control of D.melanogaster was studied by using the method of“fungus and drugs”,in order to provide reference for the control of D.melanogaster.The main results of the study are as follows:（1）Screening of highly virulent entomogenous fungi from D.melanogasterFour strains of entomopathogenic fungi were initially screened to determine the cumulative corrected mortality rate and the lethal time(LT₅₀)of D.melanogaster adults after infestation,among which two strains had a cumulative mortality rate higher than 80%and LT₅₀less than 8 d.The indoor bioassay of these two strains showed that the strain with the better pathogenic effect was Gl-fz with an LC₅₀of 1.288×10⁵spores/m L,which can be used as a potential strain for killing D.melanogaster.（2）Observation of infection process of D.melanogaster by B.bassiana Gl-fzThe infection site and process of Gl-fz strain on the body surface of D.melanogaster adults were observed by scanning electron microscopy,The conidia attached to the body surface of D.melanogaster adults were observed at1 hour,which mostly attached to the folds and depressions of the body surface,but it less distributed in the hard areas such as the chest.The conidia swelled gradually after 6 hours of infection.After 18 hours of infection,the conidia gathered in large quantity,and some conidia germinated into germ tube.After 36hours of infection,Germ tube invaded the body wall of D.melanogaster.The hyphae grew rapidly after 48 hours of infection,after 72 hours of infection,a large number of hyphae grew out of D.melanogaster,and D.melanogaster began to die.（3）Synergistic control of Beauveria Bassiana Gl-fz and plant essential oil against D.melanogasterThe inhibition rates of Dipentene diluted to 1000 times,5000 times and10000 times on spore germination of B.bassiana Gl-fz were 18.32%,15.85%and 9.70%,respectively,the inhibition rates of mycelium growth and sporulation were 19.43%,14.63%,9.55%and 42.45%,30.12%,24.55%,respectively.The co-toxicity coefficient of the mixture of Gl-fz strain and Dipentene to D.melanogaster ranged from 102.40 to 196.84,when the mixture ratio was 1:4,the co-toxicity coefficient was the highest,and all the mixtures had synergistic effect on the biocontrol of D.melanogaster.