A Preliminary Study On The Control Effect Of Entomopathogenic Fungi And Botanical Insecticides On Gonocephalum Retiulatum

The common ground beetles in China are mainly Gonocephalum retiulatum,Opatrum subaratum and G.bilibneatus.In the tobacco-growing areas of Sichuan Province,Tenebrionidae seriously harm tobacco,especially tobacco seedlings.At present,the species of Tenebrionidae in Sichuan tobacco-growing areas are not clear,and the related biological control measures are rarely reported.Therefore,this study collected the tested insects from the tobacco-growing areas of Liangshan,Sichuan Province,observed their external morphological characteristics and their living habits in the field,and determined that the main group was G.retiulatum.The 12 B.bassiana strains preserved in our laboratory were selected to compare their culture characters and pathogenicity,and the high virulence strains were screened,and their application potential in the biological control of G.retiulatum was explored.In order to preliminarily explore the possibility of application of highly virulent B.bassiana strains in the field,the compatibility of the strain with plant-derived pesticides was analyzed,and the strain was cultured against the fungi isolated and purified from the soil of Sichuan tobacco field to determine whether the fungi in the soil had an antagonistic effect on B.bassiana strains.The main results of this study are as follows:1.Morphological identification of G.retiulatumMorphological identification was based on insect taxonomy.The head,antennae,anterior chest,dorsal plate,foot and other organs of the test insect were observed by stereoscope.By referring to’Chinese tobacco insect atlas’,’Chinese crop diseases and insect pests’,’tobacco diseases and insect pests’,’Chinese crop diseases and insect pests atlas’with the main characteristics of the test insect（adult antennae were beaded,a total of 11 sections and 4sections at the end were gradually expanded,the anterior chest and dorsal plate were arc-shaped on both sides,the leading edge was concave and the leading edge angle was sharp,the sheath wing was narrow and long,and there were parallel uplift lines on both sides and the interline carving points were small;the larvae were yellowish brown,with a white shallow groove at the end of the tail and seven spines on each side.Pupae are naked pupa,milky white,abdominal end has 2 spines）,preliminary identification as G.retiulatum.2.Screening of high virulence strains of B.bassiana against G.retiulatumThe colony morphology of 12 B.bassiana strains on SDAY plate was similar,and Bb06strain had the highest sporulation and germination rate,which was significantly higher than other strains.The strain had the strongest pathogenicity to G.retiulatum.After 8 days of treatment,the cumulative corrected mortality of larvae was 83.66%,LT₅₀was 4.64 d,and the rate of cadavers was 73.33%.After 20 days of adult treatment,the cumulative corrected mortality was 82.97%;LT₅₀ was 11.09 d.The toxicity test results showed that the LC₅₀ of Bb06 strain to adults of G.retiulatum was 0.40×10⁶ spores/m L after 20 days of treatment.3.The infection process of Bb06 strain on larvae and adults of G.retiulatumThe larvae and adults of G.retiulatum were inoculated with 1.0×10⁸spores/m L suspension of Bb06 strain,respectively.The results showed that the food intake of larvae decreased on the second day of inoculation,and the vitality decreased,and the death occurred after 3⁴ days.At 2³ days after death,white hyphae were found in the head,legs,lateral valve and abdominal end of larvae,and a large number of white conidia were produced at7⁹ days after death.On the 5th day after inoculation,the activity of adults was slow,and the feeding was weakened.White hyphae appeared in the head and tail ends,and death began to occur.Over time,a large number of conidia appeared in the abdomen and back of the insect,and the whole insect was wrapped.4.Screening of botanical pesticides and their compatibility with Bb06The dipping method was used to treat the test insects.It was found that 0.3%matrine had the highest toxicity to the larvae and adults of G.retiulatum,and its LC₅₀ was 3.86 mg/L and9.47 mg/L,respectively.Different concentrations of matrine were added to SDAY plate,and it was found that after 5 days of culture,0.3%matrine with a concentration of 6 mg/L had the lowest inhibition rate on the colony of Bb06 strain,but it was still as high as 50.98%.After 10 days of culture,the inhibition rate was 42.03%.It shows that the compatibility of the two is poor,and it is not suitable for mixing in pest control.5.Identification of fungal species in tobacco field soil and determination of antagonistic effect with Bb06 strainsA total of 18 strains of fungi were isolated from tobacco field soil in Liangshan,Sichuan Province,including 15 Penicillium strains（6 P.limosum,4 P.menonorum,2 P.raperi,1 P.nepalense,1 P.simplicissimum and 1 P.citrinum）,2 Aspergillus lentulus and 1Purpureocillium lilacinum.These fungi can not inhibit Bb06 growth.After a 10 days culture,the inhibition rate on Bb06 is less than 24%.