Evaluation Of The Application Of Isaria Cateinannulata HL3 Strain Against Panonychus Citri For Biological Control

The citrus red mite（Panonychus citri）is a worldwide agricultural pest mite that has seriously affected the citrus industry causing serious damage.At present,the control of Panonychus citri is still based on chemical control.However,its resistance is becoming more and more serious due to its short generation time,serious overlapping generations and unscientific use of acaricides in the field.The application of biological control such as biological natural enemies and entomopathogenic fungi（EPF）is not only less likely to induce resistance,but also relatively friendly to the environment.Therefore,more and more attention is paid to the application of efficient biological control agents.The aim of this study was to screen out a highly pathogenic biocontrol fungal strain against P.citri and a chemical acaricide with high compatibility with this strain,as well as to evaluate its safety against predatory mites,and to comprehensively evaluate the potential of biocontrol applications of EPF.The main studies were as follows:1 Evaluation of virulence of EPF against P.citriThe pathogenicity of five EPF against was determined by inoculating conidia suspension under of lab conditions（26±2℃and 70±5%）of using spraying.HL3strain has the highest virulence with cumulative mortality of 74.23±1.88%and88.45±1.61%at concentration of 1×10⁷and 1×10⁸conidia/m L respectively,and the LC₅₀at 7 days post inoculation was about 3.40×10⁴conidia/m L.The pathogenicity of HL3 strain on non-maturing stages of P.citri was subsequently tested.The results showed that HL3 was less virulent to larva and nymph compared to adult mites,causing60.37±2.37%and 56.81±5.00%of cumulative mortality respectively at concentration of1×10⁸conidia/m L;while HL3 was the least pathogenic to egg stage with only 13.38±1.60%of mortality rate.2 Identification and observation of fungal infectionBased on the morphological and molecular identification of the fungi,strain HL3was finally identified as Isaria cateniannulata,which is second only to Beauveria bassiana in terms of distribution in forest ecology and has been reported for the control of Tetranychus urticae.The infestation process of HL3 strain was observed using fluorescein diacetate,lactophenol cotton blue and frozen section.It was concluded that the spores completed germination within 48 hours after inoculation and mycelium successfully penetrated into the mite bodies within 72 hours.The mycelium gradually covered the cuticle of the mite bodies in high humidity.3 Evaluation of the compatibility with acaricidesIn order to improve the efficiency of EPF,the effects of four common acaricides,pyridaben,fenpropathrin,bifenazate and abamectin on the growth,sporulation and germination of HL3 were determined to provide a theoretical basis for the combined application.The results proved that abamectin was the most compatible with HL3 with the lowest inhibitory effect on HL3 at three concentrations（high,medium and low concentration）.The inhibition rates of abamectin on colony growth,sporulation and germination were only 2.71%,11.03%and 7.02%respectively at the low concentration（1/8recommended concentration）,which were significantly lower than those of other three acaricides.Therefore,the combined virulence of HL3 strain and low-dose abamectin against P.citri was subsequently evaluated.The concentration of HL3 was set at 1×10⁷conidia/m L and conidia suspension was mixed with abamectin.The results showed the mortality rates were significantly higher than that of simply treated with HL3 indicating there was a good synergistic effect of combination against P.citri.4 Evaluation of the compatibility with predatory mitesIn our study,we evaluated the pathogenicity and the effect of HL3-treated on Neoseiulus barkeri’s fecundity and functional response.The results showed that the cumulative mortality rate of HL3-treated N.barkeri was only 9.17%within 7 days after inoculation,and HL3 had no significant effect on the fecundity of female adults compared with the control.However,the results based on Holling’s disc equation showed that HL3-treated prey had some negative effect on the predatory ability of the predatory mites with an increase in the handling time and a decrease in the attack rate of predatory mites.Whether the coordinated application can improve the efficiency of pest mite control in the field needs further study in the future.In this thesis,we screened the highly pathogenic HL3 against P.citri and assessed its compatibility chemical acaricides and natural enemies,and the results proved that HL3 has good potential to suppress the population of P.citri.