| Orthosia songi Chen et Zhang is one of the most important monophagous insect specifically feeding on Eucommia ulmoides leaves. O. songi population outbroke in Guizhou, Hunan, Hubei, Shanxi, Henan in rescent years, and caused serious damages to Eucommia ulmoides industry. But few studies have been conducted on the biology and ecology of O. songi, till now. In order to establish the control technology of this insect pest, studies on development duration and feeding behavior as well as the environmental impact on its occurrence were conducted from 2013 to 2014 in 30 plots in Lingbao, China. Control of O. songi was implemented by selecting envrionment friendly insecticides and control efficacy was evaluated by field application of selected pesticide. The main results are as follows:(1) It took an average 213.85 days for O. songi to overwinter, the average pupal stage was 172.40 days. During the host growing season, it took an average 59.8 days for O. songi to complete one generation; among which, the average egg stage was 4.45 days, 19.7 days for larval stage, 28.85 days for pupal stage, and 6.80 days for adult stage. O. songi larva molted 7 times, therefore its larval stage could be divided into 8 instars. The survival rate of larvae during larval stage was 98.9%. The developmental duration of other stages of overwintering generation took the same time as described above. The average food consumption for each larva is 1.65 g of fresh Eucommia leaves, and 79.71% of the food was consumed by larva from 6 instars to 8 instars. There was a significant positive correlation between larval instars and body width, body length, body weight, and food consumptions, respectively. O. songi may cause serious damage to Eucommia trees within average 20 days’ larval stage. Control of O. songi should better be completed before May.(2) Spatial distribution patterns of O. songi larva population was uniform distribution and the distribution pattern could be explained by environmental effects. The optimal sampling equation(N=[3.8416(0.022/m-0.152)]/D2) and sequential sampling equat(T(n)=0.1n±0.053n) were established.(3) Environment factors including elevation, soil depth, stand herbaceous coverage, tree height, base diameter and tree vigor had no significant correlation with O. songi population density. Aspect value was the most important predictor variable for larval density. It negatively correlated with larval density. Using a linear stepwise regression analysis method, the predictive model Y=32.42-0.03X1-6.46X2+0.06X4 was developed.(4) The characteristics of photosynthesis of damaged leaf was investiated. Results showed that net photosynthetic rate, intercellular CO2 concentration, stomatal conductance and transpiration rate of leaves being demaged were higher than that of control, and the light point also increased. The impact of different larval density on leaf loss rate and fruit drop rate were investigated. It may cause 20% fruit to drop when the density was 20 larve per 100 leaves, and 60% of leaf area were consumed when the larval density reach 16 larve per 100 leaves.(5) The results of laboratory toxicity experiments showed that LC50 of matrine were 65.30605 and 124.73585μg/L, LC50 of azadirachtin were 165.8719 μg/L and 257.7490 μg/L, LC50 of emamectin benzoate were 0.1525 μg/L and 0.2047μg/L against 3 instars and 5 instars larva respectively. Field control efficacy showed corrected mortality was 91.34% sprayed by 300,000 times dilution of 5.7% emamectin benzoate. Demonstration test results indicated that, mortality of 75000 times dilution of 5.7% Emamectin benzoate was 95.69%, significantly higher than 0.3% Matrine being diluted 750 times which was being used in practice. The cost of 5.7% emamectin benzoate was RMB 7.5 yuan/hm2, approximately 1.9% compared to matrine.The optimal control period of O. songi is in the ealry April, and control should better be completed before May. Considering the control efficacy and the pesticide cost, 75000 times dilution of emamectin benzoate is strongly recommended. |
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