POPULATION DYNAMICS AND EFFICACY OF PLANT EXTRACTS AGAINST THE SPIRALING WHITEFLY, ALEURODICUS DISPERSUS RUSSELL (HOMOPTERA: ALEYRODIDAE)

Abstract

The spiraling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae) is the most important and damaging pest of the guava orchards in Bangladesh, Seasonal abundance and population trends of spiraling whitefly, A. dispersus and their natural enemies were observed. Toxicity of eight plant extracts against A. dispersus was also studied. The result showed that September to December was the peak infestation period and almost no damage was caused from April to June. The abundance of adult, nymph and pupae of 4. dispersus were highest 5.0, 10.0 and 9.0 respectively. from September to December. The number sooty mould infested leaves were highest (93%) in the month of October to January. Ladybird beetle Scymnus sp. (Coccinellidae: Coleoptera) and Encarsia sp. (Aphelinidae: Hymenoptera) were also found as the predators of 4. dispersus during the survey. Laboratory experiments were also conducted to test the efficacy of eight plant extract against the adult 4. dispersus. Spraying (topical application) and dry film (residue on substrate) methods were used to measure the toxicity of eight plant extracts. In addition, repellency of eight plant extracts and their mixture against A. dispersus were also determined. The maximum (100%) mortality of adults was recorded for neem (ethanol) spraying at 6 hours after treatment being 500 mg/L water with 50% acetone and were followed by nisinda (acetone), ata (acetone), biskatali (acetone), vad (ethanol), vad (acetone) and akondo (ethanol) at 12 hours after treatment being 500 mg/L. In the residue on substrate experiment, the maximum (100%) mortality were recorded for neem (ethanol) at 18 hours after treatment being 500 mg/L water with 50% acetone. The mixture of plant extract neem (ethanol) + akondo (acetone); neem (ethanol) + roktokorobi (acetone) and neem (ethanol) + ata (ethanol) exhibited a significant synergism against A. disperus. Finally the repellency test of neem (ethanol) showed best response. All the applied doses has repellency and direct toxicity effect. Neem (ethanol) possess the repellency class V followed by biskatali (ethanol), biskatali (acetone) and akondo (ethanol). Therefore. the considerable infestation period of 4. disperus was trom the month of October to February and plants extract may an alternative control method to suppress the A. disperus in the guava orchard.