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Title: MORTALITY OF THE LARVAL ROOT WEEVIL DIAPREPES ABBREVIATUS L. (COLEOPTERA: CURCULIONIDAE) IN SIMULATED FLOODING OF SUGARCANE FIELDS

Author
item Shapiro, Jeffrey
item HALL, D - U.S. SUGAR CORP.
item Niedz, Randall

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: One of five species of citrus root weevils found in Florida, Diaprepes abbreviatus, causes substantial damage to roots of citrus and sugarcane stalks. The larval stage of the weevil strips bark off of a citrus root, killing it and eventually the entire tree, or bores into the base of a sugarcane stalk, weakening it and making harvesting difficult. Sugarcane growers sometimes flood their fields. Flooding of sugarcane fields was similated in the laboratory at various times and temperatures to test whether flooding of cane fields will kill and control submerged Diaprepes larvae. A statistical model indicated that good control (greater than 90% mortality) results if temperatures are high enough (24 degrees C or higher). Temperature was the most important factor in larval mortality and time was of secondary importance. Acidity increased during the experiment and oxygen decreased. Both were correlated with mortality, yet apparently contributed very little toward it compared to time and temperature.

Technical Abstract: Larvae of the weevil Diaprepes abbreviatus can cause substantial damage to sugarcane and citrus. To test the feasibility of managing Diaprepes populations by flooding canefields for extended periods of time, larval mortalities were recorded after submerging larvae under water in soil filled trays at temperatures from 18 to 17 degrees C for up to 5 weeks. Mean mortality exceeded 90% by 3 weeks of submergence at 24 and 27 degrees C and after 5 weeks at 21 degrees C, but was only 46% after 5 weeks at 18 degrees C. A model was derived by multiple regression analysis, describing the response of mortality to time and temperature as follows: x = -151.776+12.696x+10.722y-3.338x^2-0.214y^2+1.004xy, where x = time (weeks), y = temperature (degrees C), and z = arcsin-transformed mortality, with mortality as a proportion. The model accounted for 84% of the variation (r^2=0.843). Levels of oxygen and pH were monitored in selected trays during the experiment; only pH correlated significantly with mortality buy contributed only 20% of total variation (r^2=0.205) in mortality.