IMIDACLOPRID DOES NOT ENHANCE GROWTH AND YIELD OF MUSKMELON IN THE ABSENCE OF WHITEFLY

Imidacloprid is a new, chloronicotinyl insecticide currently being use d to control sweetpotato whitefly [Bemisia tabaci Genn, also known as silverleaf whitefly (Bemisia argentifolii Bellows and Perring)l. Large growth and yield increases of muskmelon (Cucumis melo L.) following t he use of imidacloprid have caused some to speculate that this compoun d may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the gr owth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal c ases on plants not treated with imidacloprid, and significant increase s in vegetative plant growth were inversely proportional to whitefly d ensities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a f ield study showed similar whitefly control and yield responses to imid acloprid and bifenthrin + endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with cont rol of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes. Che mical names used: 1-[(6 l)methyl]-4,5-dihydro-N-nitro-1-H-imidazol-2-a mine (imidacloprid); [2 methyl(1,1'-biphenyl)-3yl)methyl 3,3-trifluoro -1-propenyl]-2,2-dimethylcyclopropane carboxylate (bifenthrin); achlor o-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3- benzodiaxathiepin 3-oxide (endosulfan).