SALMA AKTER1*, MUNJURI AKTER1, MD. RAFIQUL ISLAM2 and RUHUL AMIN1
1Department of Entomology, Sher-e-Bangla Agricultural University, Dhaka-1207 and 2Department of Biotechnology, Patuakhali Science and Technology University, Patuakhali, Bangladesh.
*Corresponding author’s Email: shammi1555@gmail.com
ABSTRACT
The study was carried out at the experimental farm and research Laboratory, Department of Entomology, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh during December, 2014 to March, 2015 to study the efficacy of different chemical pesticides on mustard aphid (Lipapis erysimi) and their affect on aphid predator ladybird beetle under field and laboratory condition. The experiment was carried out under field and laboratory condition with six treatments, Morter 48EC (Chlorpyrifos) @ 1ml/l of water, Imitaf 20SL (Imidacloprid) @ 1ml/l of water, Malataf 57EC (Malathion) @ 1ml/l of water, Rison 60EC (Diazinon) @ 1ml/l of water, Actara 25WG (Diazinon) @ 0.2gm/l of water with a control. First aphids were observed on the unsprayed plot of mustard crop in the second week of January 2015 at the flowering stage of the crop (40 Days After Sowing) and their infestation continued up to 3rd week of February at the prematurity stage (75 DAS). The highest number of aphids was (230 aphid/plant) observed in the first week of February, 2015 and then their population declined gradually. Results showed that Imitaf 20SL was more toxic to the mustard aphid (L. erysimi) population, the lowest population of aphid was recorded on Imitaf 20SL (Imidacloprid) i.e. 06.33 aphids/plant, followed by Malataf 57EC, Morter 48EC, Actara 25WG and Rison 60EC. After 1 day of insecticide spraying the highest reduction of aphid population was recorded in Imitaf 20SL (91.67%). The lowest percentage of aphid population reduction was recorded in Rison (67.67%). In the control plot there was increase in aphid population in all data recording days. Significantly the highest seed yield of mustard (1355 kg/ha) was obtained from Imitaf 20SL treated plots and untreated plot produced the significantly lowest seed yield (533kg/ha). Under field condition lady bird beetle was found in the later period of the experiment. Before spray the number of lady bird beetle was around 14 in the plots. But after insecticide spraying ladybird beetle number were reduced drastically and highest 84 percent mortality of the predator was observed in the Imitaf treated plot. The lowest mortality of lady birds was found in the untreated plot indicating the devastating effect of the insecticides on the predator of aphid. Under laboratory condition the highest percentage of mortality of aphid (84%) as well as the ladybird beetle (91%) population was found in the Imitaf treatment and other treatments also showed a decreasing trend. But the untreated petridishes showed the reverse result. Insecticides are needed for pest control; on the contrary they have devastating effect on the natural enemies of the pests. So it’s time to optimize the use of the insecticides to protect those natural friends and to reserve our environment.
Keywords: Mustard aphid, Ladybird beetle and Insecticides.