| Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) has been considered as one of the most serious pest that causes direct damage and could act as a vector of viral plant disease on the vegetables and ornamentals in the greenhouse and fields crops, in most countries and regions of the world. It has also been reported as a pest of various crops in 22 provinces or cities in China. Recently the whitefly pest has become a severe problem with the serious damage to vegetables and ornamental crops in China. Biological control is one of the most effective strategies for management of B. tabaci. An entomopathogenous fungus, e.g. Verticillium lecanii is the alternative approach for biological control strategy and the insecticidal toxin from the secondary metabolites of entomopathogenous fungi could be exploited as important insecticidal products for control of the sucking insects e.g. B. tabaci, which is significant in the theory and practice for biological control of insect pest. Here, we first systematically reported the selection and culture for the strains with the most productive abilities for toxins among V. lecanii strains from Canada and China, the extraction and preliminary identification of the toxins, the biological activities on B. tabaci, and then the control effect on the population of 5. tabaci and its application. The main results are as follows.1.Comparison of the culture and morphological characteristics of the 5 domestic and one Canadian strains were conducted under the light microscope. The results showed that the culture and morphological characteristics of the 6 strains are similar, but with the difference in the stem of the conidial spore and the volume size of the conidial spore. The strain V3450, derived from B. tabaci, has longer stem of conidia (16.0um) and bigger size of conidia volume (5.0-6.0x1.1-1.5um), while the strains V341and V342, derived from Anoplophora chinesis, have smaller size of conidia volume (1.6-2.0x0.6-0.8um). The imported strain V16063 has the shortest stem of conidia (0.2-0.5 urn).Bioassays of the 6 strains of V. lecanii were conducted on the B. tabaci. For inoculation, batches of 3rd instar whitefly nymphs on sweet potato seedlings were immersed in conidial suspensions at concentration from 103-107 conidia/mL. The virulence of the 6 strains of V. lecanii for B. tabai was compared after the construction the Time-Dose-Mortality model. Results indicated that the strain V16063 imported from Canada and the domestic strains V3450, Vp28 derived from B. tabaci and scale insect,respectively, were more virulent than the others with the LC50 values of 2.57 x 105,6.03x 105 and 6.03 x 105 conidia/ml, respectively.Comparisons of the bioactivity effect of dilutions of the crude extract from 6 strains of V. lecanii on 1st instar nymph of B. tabaci were conducted by the bioassay approach and the results showed that the dilutions of crude extracts from the strains V3450, Vp28 and V16063 were more virulent than the other 3 strains. The mortalities to the 1st instar of B. tabaci were 80.27%, 71.90% and 66.66%, respectively. Based on the comparison of the bioactivity effects of dilutions of the crude extract under culture with the 7 ferment liquid media on the lst instar nymph of B. tabaci, 2 liquid culture media, the innovated Czapek media and the innovated wort media were selected as the superior ferment media for experimental and massive culture of the V. lecanii producing the toxin with the mortalities to the 1st instar of B. tabaci of 80.27% and 71.90%, respectively.2.The crude toxin from mycelia (named as MY crude toxin) and metabolites (named as MO crude toxin) were yielded after multiple extractions with organic solvent. The bioactive compounds (Toxin-IV, Toxin-VD, Toxin-X, Toxin-X II and Toxin-VIIIMO ) to B. tabaci were isolated from the MY crude toxin and MO crude toxin with various chromatographies. Analyses of the infrared (IR) spectrum gave a preliminary identification of these toxins. Toxin-IV is a cyclic compound containing amide, ketone and ester; Toxin-VD a...
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