Pathogenicity Of Beauveria Bassiana On Delia Antiqua (Meigen)

The onion maggot, Delia antiqua (Meigen), is an important pest threatening garlic, onion and other crops in the the Lily family. By far, the most common method to control onion maggot is to apply insecticides when watering garlic in field, which leads to insecticides residue, resistance and environmental pollution. As it was reported, Beauveria bassiana had significant inhibitition effect on Diptera insect pests. We found that onion fly could be infected by B. bassiana in the field, so the study determined the initial activities of 4 strains of B. bassiana against Delia antiqua (Meigen) adults and larvae and the virulence against the high sensitivity insect state and described the symptoms of onion fly. Then the growth and reproduction of onion fly at 0-1 days old was measured with the sublethal dose of the high virulence strain and compared the effect of the effect of B. bassiana on age-specific adult mortality and fecundity of onion fly. The effects of B. bassiana on physiological and biochemical characteristics of the onion fly were also studied. The main results were as follows:1. B. bassiana had high virulence on onion fly than larvae. The corrected mortality of onion fly were more than 50% after treated 7 days by four strains of B. bassiana. at doses of 1.0×108 conidia/mL, even the corrected mortality of high virulence strains reached 94.9% and 92.3%, respectively. The tested strains had no pathogenicity to the 1 and 3 instar larvae with the corrected mortality was less than 10%. B. bassiana that had high virulence on onion fly was collected.2. Pathogenicity of 4 strains of B. bassiana strains was different on onion fly. Bb01 and Bb03 strains had rapid effects on onion fly with the LT50 were 3.28 days and 3.44 days, respectively. The pathogenicity of BbO2 and Bb04 strains was slow, and their LT50 were 6.95 days and 6.92 days, respectively.As to the stomach virulence, B. bassiana Bb01 showed the highest virulence on onion fly with LC50 values of 1.76×106 conidia/mL. B. bassiana Bb03 and Bb02 had higher virulence with LC50 values of 4.05×106 and 1.86×107 conidia/mL, respectively. B. bassiana Bb04 showed the less virulence and its LC50 was 2.37×107 conidia/mL.3. Onion fly showed obvious symptoms after infected by B. bassiana. The action of treated onion fly was gradually slow and the treatment caused convulsive symptoms of foot when walking. The thoracic legs of dead adults were stiff and hanging in the larger friction cages wall. The dead adults put in the culture dish with moist filter paper, the fungal mycelium began to grow after 3-5 days under the condition of 25 ? and the fungal mycelium emerged through the soft parts of the exoskeleton, such as the wing bases, intersegmental regions of the legs and membranous regions of the abdomen.4. The effects of high virulence strains Bb01 and Bb03 were determinated on sublethal dose LCio, LC30 and LC40 on onion fly aged at 0-1 days old. All the treatment had adverse effects on development and reproduction. Two strains of B. bassiana could prolong the preoviposition period of onion fly. The preoviposition period were extended by 3.75 days and 2.25 days treated by sublethal dose LC40 of Bb01 and Bb03 strains compared with control. Both Bb01 and Bb03 strains had a great influence on the lifetime of the adult, especially the lifetime of the female adult. The sublethal dose of B. bassiana had obvious effect on fecundity. Fecundity of adults were reduced by 51.9%,75.2% and 92.2% when onion flies were treated by the doses of LC10, LC30 and LC40 of Bb01 strain compared with the control, and fecundity of adults treated by Bb03 strain decreased by 40.0% and 69.4% and 83.3%, but hatch rate had no significant difference.5. B bassiana showed age-specific effect on onion fly and had obvious effects adults aged at 0-1 than 9-10 days old with the decrease of survival rate and fecundity. But fecundity of age-specific adults decreased significantly treated in high concentration. However, the hatch rate had no significant effect.When age-specific adults were treated by high virulence strain Bb01 with the dose of 5.8×103 conidia/mL,1.7×105 conidia/mL and 5.7×105 conidia/mL, adult mortality and fecundity had a significant difference, but hatch rate had no significant effect. Adult mortality aged at 0-1 days old treated by three concentrations of Bb01 strain were 17.5% and 35.5% and 47.5%, though adult mortality aged at 9-10 days old were 12.5%,25.0% and 37.5%. The result showed that B. bassiana had more influence on mortality of younger adult. Fecundity of 0-1 days onion fly treated with the dose of 5.8×103 conidia/mL and 1.7×105 conidia/mL were 51.9 and 21.8,51.9% and 75.2% lower than the control, respectively. But fecundity of 0-1 days onion fly were 92.4 and 46.1 in the same concentrations and reduced by 21.6% and 60.8%, respectively. The result showed that B. bassiana had more influence on fecundity of younger adult than older adult. However, B. bassiana had better control effect on fecundity of age-specific adults in concentrations of 5.7×105 conidia/mL with the fecundity of adults aged at 0-1 and 9-10 days old were 8.4 and 20.6,92.2% and 82.5% lower than the control, respectively.6. B. bassiana Bb01 had effect on physiological and biochemical characteristics of the 0-1 days old onion fly treated with 1.0×107 conidia/mL. Both the protein content and activities of protective enzymes SOD, POD and CAT showed a trend of increased first and then decreased compared with the control. However, the activity of SOD reached the maximum value in the first day after treated, while the activity of POD gradually increased and reached the highest in fourth days. In addition, the activity of CAT had been higher than the control and reached the maximum value in third days. Three kinds of protective enzymes played a role in the process of insect adverse effects, while the times were different.