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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #134573
Title: SUSCEPTIBILITY OF DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) TO A COMMERCIAL PREPARATION OF BACILUS THURINGIENSIS SUSP. TENEBRIONIS.

Author
item Weathersbee Iii, Albert
item TANG, Y.Q. - FUIJAN AG UNIV, CHINA
item DOOSTDAR, HAMED - MORSE ENTERPRISES
item Mayer, Richard

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2002
Publication Date: 6/1/2002
Citation: Weathersbee Iii, A.A., Tang, Y., Doostdar, H., Mayer, R.T. 2002. Susceptibility of diaprepes abbreviatus (coleoptera: curculionidae) to a commercial preparation of bacilus thuringiensis susp. tenebrionis.. Florida Entomologist.

Interpretive Summary: The most ecomically important insect pest of citrus in Florida is the Diaprepes root wevil. Damages caused by this weevil to Florida citrus growers have been in excess of $300 million since 1997. This pest also attacks sugar cane, vegetable crops, and ornamental plantings. Economic losses to these crops are also substantial, but have not been estimated. We have been studying the potential for control of Diaprepes root weevil with the bacterial pathogen, Bacillus thuringiensis. This bacterium produces a protein that is toxic to insects upon ingestion. Some newly hatched weevil larvae died after ingesting insect diet that contained the bacterium but the greatest effect was a reduction in their weight gain. Larvae exposed to the bacterium at five or 12 weeks old were highly susceptible. The degree of mortality in these older larvae strongly depended on the amount of bacterium in the diet but it was effective at very low levels. The results of our studies indicate that B. thuringiensis may be useful in controlling root weevil larvae in citrus and other horticultural crops.

Technical Abstract: The root weevil Diaprepes abbreviatus (L.) was evaluated for susceptibility to spore/endotoxin complexes produced by Bacillus thuringiensis subsp. tenebrionis (Btt). A reduction in survival was observed for neonate larvae exposed to either insect diet or potted citrus treated with Btt. A reduction in weight gain of neonates was indicated only on the Btt-treated diet. Larvae that were exposed to Btt-treated diet at five weeks old exhibited a strong dose-dependent mortality response but mortality was delayed. The mean ages at death ranged from 111 to 128 days among the treated larvae. The LC50 for larvae in this age group was 6.2 ppm [AI] and the slope of the probit line was 2.29. The mortality response of larvae exposed at 12 weeks old also was done dependent with a delayed period to mortality. The mean ages at death ranged from 130 to 141 days among the treated larvae. The LC50 for larvae in this age group was 25.4 ppm [AI] and the slope of the probit line was 2.75. A bimodal distribution observed for Btt-induced mortality with respect to larval age was similar to the pattern of midgut trypsin activity with respect to developmental age in D. abbreviatus, indicating that the delayed mortalies observed here may be due to endotoxin activation only during particular stages of larval development. The results of this experiment indicate that Btt may have utility in pest management programs directed against D. abbreviatus.