Antifeedant Effect Of The Sublethal Dose Of Neonicotinoid Insecticides On Sitobion Avenae And Aphis Gossypii

The neonicotinoid insecticides represented by imidacloprid is a new type of insecticide with significant root systemic applicability,and is widely used in production to prevent aphids and other sucking pests.Studies have shown that neonicotinoid insecticides seed dressing of wheat can control efficiently wheat aphid during the whole growth period,whereas the mechanism still needs further study and discussion.In addition,compared with wheat plant,the control effect of neonicotinoids on Aphis gossypii by seed dressing of cotton can only maintain about 40 days.Based on these results,the antifeedant effect and its'preliminary mechanism of the sublethal dose of neonicotinoids on Sitobion avenae and Aphis gossypii were studied.Firstly,the sublethal dose of neonicotinoids on the two important crop aphids,were determined by hydroponics,followed by the antifeedant effect of sublethal dose of neonicotinoid insecticides on tested aphid species was cleared by mark method with trace element Rb,honeydew method and the changes of total sugars and total lipids content of aphids.The preliminary study of the antifeeding mechanism of the sublethal dose of neonicotinoids on tested aphids were studied with EPG and the determination of amino acid content in the leaves of wheat and cotton plants.This study will provide a theoretical basis for better promoting the rational application of neonicotinoid insecticides on sucking pest control.1.Determination of optimal conditions of hydroponics and the sublethal dose of neonicotinoids on tested aphidsThe contents of imidacloprid in different parts of wheat and cotton plants treated by hydroponics were determined by UPLC-MS/MS.The results showed that imidacloprid has high root absorption and systemic characteristics in wheat and cotton plants.The content of imidacloprid in the aboveground parts of wheat plants was generally higher than the roots,or no significant difference between the two parts.Whereas the retention of imidacloprid was significantly higher in cotton roots than that of other parts,and there was no significant difference between cotyledon and true leaf.With the multiplication of the treatment dose,the residue of imidacloprid in wheat plants was nearly saturated at the treatment dose of 12.5²5 mg/kg.Basis on this,the toxicities of seven neonicotinoids and pymetrozine on tested aphids were determined by hydroponics,and the sublethal doses of each insecticide were calculated.2.Antifeedant effect of the sublethal dose of neonicotinoids on tested aphidsThe effects of sublethal dose(LC₂₅)of neonicotinoids on the feed intake of S.avenae and A.gossypii were measured by Rb mark method,honeydew method,analyzed of the total sugars and total lipids content in aphids.The results of Rb mark method and honeydew method showed that the antifeedant rates were all above 80%of sublethal dose of neonicotinoids on S.avenae.But the antifeedant rates were all below 25%of sublethal dose of neonicotinoids on A.gossypii.The results of the total sugars and total lipids content in neonicotinoids treated aphids indicated that the content of total sugars and lipids in S.avenae was significantly lower than that in the control,while there was no significant difference between treated A.gossypii and control.The results of three methods are indicated that the sublethal dose of neonicotinoids has a significant antifeedant effect on S.avenae,and there is no obvious antifeedant effect on A.gossypii.3.Effects of sublethal dose of neonicotinoids on feeding behavior of tested aphidsThe feeding behavior of S.avenae and A.gossypii were investigated by EPG.The results indicated that the non-feeding time and frequency?np waveform,C waveform and pd waveform?were significantly higher than that in the control,but the feeding time?E1waveform and E2 waveform?were significantly shorter than that in the control.This indicated that the sublethal dose of neonicotinoids hindered the feeding behavior of S.avenae.The antifeedant effect of the sublethal dose of neonicotinoids on S.avenae was due to the inhibition of the feeding behavior.Whereas there was no significant difference in the feeding time,non-feeding time and frequency between neonicotinoid treated A.gossypii and the control.Thus,the sublethal dose of neonicotinoid insecticides had no obvious inhibitory effect on the feeding behavior of A.gossypii.4.Effects of systemic absorption of neonicotinoids on free amino acid content in crop leavesThe results of the free amino acid type and content in the leaves of wheat and cotton treated with the sublethal dose of neonicotinoids showed that the contents of threonine,serine,leucine and histidine and the total amount of amino acids in wheat leaves were significantly higher than those in the control.The content of the rest amino acids were not significantly different between the treatments of neonicotinoid and the control.The contents of threonine,serine and tyrosine in cotton leaves neonicotinoid treatments were significantly lower than those in the control.The rest of the amino acids and the total amount of amino acids were not significantly different between the treated plants and the control.Thus,the changes of certain amino acids content in wheat plants after the systemic absorption of neonicotinoid insecticides maybe affect the feeding behavior of S.avenae.