Seasonal incidence, fliar damage and chemical control of Thysanoplusia orichalcea Fabr. (Lepidoptera: Noctuidae)-A Pest of sunflower

Abstract

The semilooper, Thysanoplusia orichalcea Fabr.,(Lepidoptera: Noctuidae) moult four times and complete its stadial period in 37.79±1.9 days during five instars. The entire eco-physiological experiment on larval period was conducted under 15.0±2.1 (min.), 19.4±2.8°C (max.) temperatures with 85.0±2.5% relative humidity at 12 h. of L: D periods. Amale larva ingests more of leaves at I and V instars whereas the female has more feeding values on the remaining instar of II, III and IV. The I and II stage larvae consumed 129.67 mg of leaves whereas the consumption has been 8923±2.19 mg per'd1 for III to V instars. The consumption at two sexes level is different i.e., 9082.36 mg for the male and 8811.61 mg for the female larvae. Thus the total amount of food consumed against per mg of body weight by the larvae observed from I to last instar viz., 2.38, 1.73, 1.75, 1.55 and 0.86 respectively. Four different synthetic pyrethroids viz., Deltamethrin, Cypermethrin, Fenvalerate and Permethrin were tested in order to identify the best chemical for reducing the population of T. orichalcea. The results indicated that the LC5Oand LD50 for deltamethrin was 0.000095% and 0.03496 ug/g of body weight of third instar larvae respectively. Similarly LC50 for cypermethrin, fenvalerate and permethrin was 0.00027,0.00095 and 0.001117% respectively whereas LD50 was 0.07878, 0.1196 and 0.1502 (ig/g of body weight respectively. The data of LD5o reveals that the deltamethrin is the most toxic and permethrin is least toxic against T. orichalcea. The order of relative efficacy based on LT5o values of these insecticides were deltamethrin 0.001%, cypermethrin 0.01%, fenvalerate 0.01% and permethrin 0.05%.