Bemisia tabaci, sweetpotato whitefly, has been recognized one of the most destructive insect pests worldwide because of increased resistance to some insecticide groups requiring alternative strategies for its control. We conducted a study of the influence of relative humidity, temperature and different developmental stages on the susceptibility of sweetpotato whitefly to conidia of Isaria javanica isolate, which had been reported high virulence against Q biotype of B. tabaci. The mortality of tobacco whitefly was low at low constant relative humidities, but was high when kept high humidity for first 24 hours and transferred to low humidity. The Isaria isolate had wide range of temperature (15℃ to 35℃) to control sweetpotato whitefly. The isolate has virulence to the egg and all developmental stages of nymph of B. tabaci. These results indicated that the isolate had good control effects at various environmental conditions and is an excellent candidate to develop a microbial pesticide to control sweetpotato whitefly.

Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of worldwide because of increased resistance to some insecticide groups requiring alternative strategies for its control. We studied the susceptibility of this biotype of B. tabaci to 21 isolates of Beauveria bassiana, 3 isolates of Isaria spp., 1 isolate of P. cateni，3 isolates of Lecanicillium lecanii, 1 isolate of L. attenuatum and 1 isolate of Aschersonia aleyrodes. These isolates were evaluated on pruned egg plant seedlings, at a concentration of 108conidia/ml (deposited at 6000±586 conidia mm-2). The mortality based on mycosis varied from 18 to 97% after 6 days. An Isaria sp. isolate, two B. bassiana isolates and a L. lecanii isolate were found the most effective. Furthermore, five isolates were chosen for concentration-mortality response assays and compared to B. bassiana GHA as a standard. The numbers of nymphs infected by fungi were correlated with the spore concentration. A L. lecanii isolate and Isaria sp. had the short LT50 at 6000±586 conidia mm-2. Mortality reduced and LT50s were longer as the concentration of conidia was reduced. The LD50 values were differed in isolates from 87 to 269 conidia mm-2. These results indicated that the Q biotype of sweetpotato whitefly was susceptible to the five isolates of entomopathogenic fungi and these isolates have potential to be developed as a microbial pesticide for whitefly control.

Two-spotted spider mite, Tetranychus urticae (Koch) is one of the serious pests in economically important crops such as strawberry and cucumber and so on. Acaricides have been used as the main control agents. This study was conducted to test the synergistic effects of the Beauveria bassiana GHA, which has been registered for whitefly and thrips, and five pesticides (abamectin, acrinathrin, bifenthrin imidacloprid, dinotefuran, and indoxacarb, which are commonly used pesticides in strawberry in Korea), on the two-spotted spider mite T. urticae. Five tested pesticides did not inhibit spore germination and mycelial growth of B. bassiana. Pesticides were applied to potted strawberry plants at four different treatments (recommended concentration, 1/5 recommended concentration, 1/5 recommended concentration + GHA(108 conidia/ml), and only GHA(108 conidia/ml). Mortality in larvae of two-spotted spider mite was 12% in GHA 5 day after treatment. Mortality in abamectin treated T. urticae was 98.5% and 100% at 1/5 recommended concentration and recommended concentration, respectively, 3 days after treatment. Acrinathrin, indoxacarbe, dinotefuran and difenthrin imidacloprid caused 60%, 14%, 16% and 91% mortality at recommended concentration 5 day after treatment. The tested five pesticides and B. bassiana GHA had no synergistic effect.

The first commercial bioinsecticide in Korea was registered in 2003 to control diamond back moth and beet armyworm in Chinese cabbage using Bacillus thuringiensis subsp. aizawai. Currently, fourteen microbial pesticides have registered in Korean market. The Korean government is aiming for 40% reduction (from the 2004 value) in the use of chemical pesticides by 2013. To increase the use of microbial pesticides as an alternative of chemicals, we conducted in vitro bioassay with Bt products. Bt products were treated alone and in combination against larvae of beet armyworm, diamond back moth and tobacco cutworm. Five Bt products shown high mortality against diamond back moth in recommended concentration, but had low control effects against beet armyworm and tobacco cutworm. Mixed Bt products had no synergic effects against the tested three moths. When Bt products were sprayed with higher concentration than recommended dose, those mortality was similar with lower concentration.