INCIDENCE AND CONTROL OF THRIPS TABACI (THYSANOPTERA: THRIPIDAE) ON ONION USING NEEM LEAF EXTRACTS

Abstract

The experiment was conducted to study the incidence of onion thrips, Thrips tabaci (Lindeman) in field conditions and mortality also tested using three different solvent (acetone, petroleum benzene and distilled water) extracts of neem leaf powder in the laboratory of the Department of Entomology, HSTU, Dinajpur during the period from November, 2015 to April, 2016. Results showed that the highest number of thrips was observed at the end of March, 2016 while the lowest was 3.93 due to heavily rainfall on 29 March, 2016. The average number of nymphs per plant was 4.91 when plant height was 39.49 cm then the number of nymphs increased up to 20.37 when the plant height was 42.78 cm. The maximum number of thrips (20.37) was observed at the end of March, 2016 when the mean number of leaves per plant was 4.11. The number of thrips per plant was negatively correlated with leaves per plant and plant height. Weather parameters (temperature, humidity and rainfall) had great influence on incidence of onion thrips population. In case of temperature, thrips population gradually increased with increasing average temperature at a certain level. On the other hand, thrips population decreased with increasing relative humidity and rainfall (cm). Among the tested extracts, acetone extract of neem leaf powder provided the highest mortality (33.67%) while the extract with distilled water caused the lowest mortality (12.33%). In case of control treatment, no mortality of thrips was found. The lowest LDso values of acetone extract of neem leaf powder at 1, 2, 3, 4 and 5 HAT indicated that acetone extract possessed the highest toxic effects. Acetone extract was highly toxic to nymphs of onion thrips and which provided 100% mortality within 5 hours after exposure. The LT so (h) values of acetone extract (1.56) provided best performance among the tested extract. It is revealed from the results that plant height, number of leaves and weather parameters have influence on incidence of onion thrips population. It is also revealed that acetone extract of neem leaf powder performed well to check the T. tabaci infestation.