Author
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Weathersbee Iii, Albert |
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TANG, Y.Q. - ORANGE COUNTY, FLORIDA |
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Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/12/2002 Publication Date: 4/1/2002 Citation: N/A Interpretive Summary: The Diaprepes root weevil, Diaprepes abbreviatus (L), is an important exotic insect pest of Florida citrus. Larval feeding on the roots of citrus causes injury that leads to yield reductions, enhanced susceptibility to disease, and eventually death. Profit losses to the citrus industry are due to the reduced yields, cost of control and replant ing of trees. We evaluated a commercially available neem seed extract (Neemix, containing 4.5% azadirachtin [AZA]) to determine if it had biological activity against Diaprepes root weevil eggs, larvae and adults. Newly hatched and three week old larvae exposed to sliced carrot treated with the extract exhibited dose-dependent mortality and reduced weights among survivors of treatments. The effect on weight gain was most pronounced for both larval age groups. Newly hatched larvae exposed to an insect diet incorporated with the extract at 43 ppm AZA had growth inhibited by more than 97% as compared to the control larvae. A soil drench containing 30 ppm AZA reduced the survival and weight gain of newly hatched larvae added to potted citrus and provided protection to the citrus roots in a greenhouse experiment. A soil drench containing 90 ppm AZA was required to provide protection of roots against four week old larvae. Reproductive effects were observed when adult weevils were fed citrus foliage treated with the extract. Larval hatch per egg mass were reduced by 27% and 68% at 30 and 90 ppm AZA, respectively. These results suggest that neem seed extract may be useful in managing Diaprepes root weevil in citrus. Technical Abstract: A commercially available neem seed extract (NSE), containing 4.5% azadirachtin (AZA), was assessed for biological activity against the Diaprepes root weevil, Diaprepes abbreviatus (L.), an important exotic insect pest of Florida citrus. Laboratory bioassays against neonatal and 3-week old larvae fed sliced carrot treated with NSE produced dose- dependent larval mortality and reduced fresh weights among survivors of treatments. The weight response was greater than the mortality response for both larval age groups. Neonates treated with 45 ppm AZA weighed 60% less than those in the control after four weeks. Three-week old larvae treated with 45 ppm AZA weighed 30% less than those in the control after five weeks. When neonates were exposed to insect diet incorporated with NSE, reductions in larval survival and weight were observed at concentrations as low as 4.8 ppm AZA after six weeks. Larval growth was inhibited by more than 97% with 42.9 ppm AZA in the diet. A soil drench containing 30 ppm AZA reduced the survival and weight gain of neonates added to potted citrus and provided protection to the roots in a greenhouse experiment. A concentration of 90 ppm AZA was required to provide protection of citrus roots against 4-week old larvae. Reproductive effects were observed when adult weevils were fed foliage treated with NSE. The numbers of larvae hatching per egg mass were reduced by 27% and 68% at 30 and 90 ppm AZA, respectively. These results suggest that NSE should be further evaluated for use in IPM programs of citrus. |
