Study on the Synergistic Control Effect of Metarhizium rileyi and Harmonia axyridis Toward Aphids
[Objective]The purpose of this study is to clarify whether the combination of Metarhizium rileyi and Harmonia axyridis can achieve synergistic effect,and to provide theoretical basis and application technology for efficient biological control of aphids.[Method]The direct and indirect pathogenicity of M.rileyi to adult H.axyridis was measured by spraying adult H.axyridis with M.rileyi conidia and feeding H.axyridis with aphids after spraying,the H.axyridis without spraying M.rileyi and the H.axyridis fed with aphids without spraying M.rileyi were used as controls,respectively.After spraying the aphids with conidia of M.rileyi,the feeding selectivity of the H.axyridis to aphids under different starvation times was measured.In order to clarify the impact on the aphid predation ability of H.axyridis after feeding on aphids treated with M.rileyi,the predation function,egg production,and egg hatching rate of the H.axyridis were determined after feeding on aphids treated with M.rileyi.Two treatments were set up to determine the jointly control effect of H.axyridis and M.rileyi on aphids using the reduction rate of insect population as an indicator,one of which was to apply M.rileyi before releasing H.axyridis,and the other was to release H.axyridis alone.[Result]The evaluation of direct and indirect pathogenicity showed that the survival rate of H.axyridis was not significantly different from that of the control group.At 0 h of starvation treatment,the feeding preference rate of H.axyridis to Acyrthosiphon pisum was significantly lower than that of the control group,but there was no significant difference between the two groups at 24 and 48 h of starvation treatment,which was consistent with the conclusion of predation functional response model.The instantaneous attack rate of H.axyridis against A.pisum in M.rileyi treatment group and control group was 0.6585 and 0.6479,respectively,with no significant difference(P＞0.05).The total number of eggs laid by single female H.axyridis in M.rileyi treatment group and control group for 7 consecutive days was 161.67 and 167.33,and the egg hatching rate was 65.60%and 67.60%,respectively,with no significant difference(P＞0.05).The treatment of releasing H.axyridis after applying M.rileyi showed better control effect on A.pisum on the 2nd to 3rd day and Rhopalosiphum maidis on the 2nd to 4th day after the release of H.axyridis.[Conclusion]M.rileyi had no significant effect on the predation ability,egg production and hatching rate of H.axyridis,and the control effect of H.axyridis on aphids was improved after the application of M.rileyi,and the two agents had a synergistic effect.
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