| Mirids have historically been considered minor pests of cotton and other crops in China.But since the advent of Bt-cotton in 1997 they have gradually become major pests of cotton.In china,the management to mirid populations is keeping on strengthens because the damage caused by this pest is increasing.Chemical control is relied on heavily for mirids because it's high efficiency and quick-acting.Frequencies and areas of insecticide applying for suppressing mirid bugs are increasing.Excessive and unreasonable use of chemicals will inevitably result in resistance to the insecticides used against target insects and environment pollution.Biological pesticide uses biological living or their metabolites to control pest.Applying biological pesticide is one of the most important measures in biological control,which helps to reduce the selection pressure of chemicals,delay resistance in pest and protect environment.Hence,we monitored the resistance level of mirid bugs populations from different areas to four insecticides.Biological pesticides against mirid bugs were selected in laboratory and field.On this basis,the infection process of Beauveria bassiana and Metarhizium anisopliae were investigated and the pathogenic mechanism of these two fungi to mirid bugs was discussed.These results will enrich biological control to mirid bugs and provide theoretical foundations and data references for the integrate pest management.1.Resistance monitoring of populations in Apolygus lucorum and Adelphocoris suturalisTo investigate insecticide resistance levels in different A.lucorum and A.suturalis populations and to thereby improve both the chemical control of this pest and resistance management,samples of populations were collected from the Yellow River Cotton Growing Area(YRCA)and the Changjiang River Cotton Growing Area(CRCA)between 2011 and 2014 and their resistance to beta-cypermethrin,chlorpyrifos,emamectin and fipronil was measured in a glass-vial bioassay.Compared with a susceptible laboratory strain,A.lucorum populations from Nanjing in Jiangsu Province and Chuzhou in Anhui Province(CRCA)were still susceptible to the four insecticides(<5-fold resistance),but populations from Yancheng in Jiangsu Province(CRCA)had low levels of resistance to beta-cypermethrin(3.4-8.5 fold resistance)and chlorpyrifos(3.3-5.8 fold resistance).However,A.lucorum populations collected from Anyang in Henan Province,Binzou in Shandong Province and Cangzhou in Hebei Province(YRCA)had developed low to middle levels of resistance to beta-cypermethrin(7.1-22 fold),chlorpyrifos(5.2-20 fold)and fipronil(1.6-10.3 fold),were still susceptible to emamectin(0.9-2.6 fold).A.suturalisis occures in the Changjiang River Cotton Area(CRCA).The result showed that populations from Chuzhou of Anhui Province(CRCA)were still susceptible to the four insecticides(<5-fold),and populations from Jinzhou of Hubei Province,Yancheng and Nanjing of Jiangsu Province(CRCA)had low levels of resistance to chlorpyrifos(0.5-1.9 fold),emamectin(0.2-1.6 fold)and fipronil(0.25-3.2 fold),but developed low to middle levels of resistance to beta-cypermethrin(1.8-10.0 fold).Variation in susceptibility to the 4 insecticides was less than 3 fold between years for each of the 6 monitoring locations.Differences in resistance levels between populations in the YRCA and CRCA may be attributed to the history and the amount of insecticide used locally to control A.lucorum.2.Selection of biological pesticide for control mirid bugsThe laboratory and field trials of four biological pesticides to mirid bugs was carried out.The results showed that the corrected control effects in laboratory of 2×10~10 conidia/g B.bassiana DP,2X1010conidia/g M.anisopliae DP,1×1010 conidia/ml E.brevis SC and 5%Emamectin benzoate EC were 94.06%,95.93%,99.54%and 97.67%,respectively 7 days after spraying,which were significantly better than that of 40%profenofos·phoxim EC(86.25%).The corrected control effects in field of 4 biological pesticides were 44.39%,49.04%,58.47%and 73.26%,respectively.The efficacy of emamectin was significantly higher than that of profenofos·phoxim(58.89%)and there was no difference between other 3 biological pesticides and profenofos·phoxim EC.The four biological pesticides showed good biocontrol effects on mirid bugs.3.Infection processes of B.bassiana and M.anisopliae to the Adelphocoris suturalisThe infection processes of B.bassiana and M.anisopliae against A.suturalis were observed using scanning electron microscope.The results showed that time dynamic of infection processes of two fungi were the same.First,fungi attached on the cuticle ofA.suturalis,then began to secrete extracellular mucilage to reinforce the adhesion after 12 hours of inoculation.The adhesion of conidia was affected by the physical structure of A.suturalis cuticle.Most of conidia were deposited on cavities,setae and folded regions,but less conidia attach on the smooth and hard areas.The conidia germinated to form appressoria and germ tube after 16 hours of inoculation and germ tubes developed into hyphae after 20 hours,then appressoria,conidia,and hyphae released extracellular hydrolyzing enzymes to dissolve A.suturalis cuticle in 24 hour.After 36 hours,hyphae penetrated into the body wall of A.suturalis with the aid of mechanical stress of themselves.The hyphae penetrated out from A.suturalis cuticle and developed to aerial hyphae after 48 hours.Conidia scattered and infected into other host after they matured.4.The pathogenic mechanism of B.bassiana and M.anisopliae to A.lucorum and A.suturalisThe relationship between toxicity and biological characteristics,infection processes,proteinase activity of B.bassiana and M.anisopliae was investigated.The results showed that the toxicity of ?-Bb,B.bassiana strain and ?-Ma,M.anisopliae strain to mirid bugs were higher than other strains.?-Bb and ?-Ma The growth rate of ?-Bb and?-Ma were faster than other stain,which colony diameter were 84.16 and 83.89mm,respectively after 96 hours of inoculation.The amount of spores produced were highest,which were 61.55 and 6.20 X l0~9 conidia/ml,respectively.After 24 hours of infection,high toxicity strains ?-Bb and ?-Ma produced more conidia and grew faster on the cuticle of mirid bugs than low toxicity strains VI-Bb and ?-Ma.After induced,the protease activity in ?-Bb and ?-Ma media supernatant was 5.7 to 7.7 times higher than that in strains of lower toxicity.These results indicated that the biological characteristics,infection process and induced protease activity of B.bassiana and M.anisopliae affected their toxicity to mirid bugs. |
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