Vulnerability of Stressed Palms to Attack by Rhynchophorus cruentatus (Coleoptera: Curculionidae) and Insecticidal Control of the Pest

Abstract

One field study and two experiments were done to test whether palms must be stressed for successful infestation by Rhynchophorus cruentatus (F.). In the field study, 8% of 290 transplanted mature cabbage palmettos, Sabal palmetto (Walter), in a site in Broward County, Fla., became infested with immatures of R. cruentatus and died, compared with no infestations or mortality in a control group of 92 undisturbed palms after 140 d. In Experiment 1, 2-yr-old potted Canary Island date palms, Phoenix canariensis Hortorum ex Chabaud, were grown in a screened enclosure and either stressed by severe pruning or left unstressed. All palms were bagged with fine-meshed polyethylene netting and each was challenged with two male and two female R. cruentatus . Thirty-one percent of the 13 stressed palms were infested with immatures of R. cruentatus and died within 56 d compared with a 15% infestation and mortality level in 13 unstressed palms. In Experiment 2, finemeshed polyethylene bags were used to confine 10 males and 10 females of R. cruentatus onto individual mature cabbage palmettos in the field that were either stressed by severing of the stem or unstressed. All of the three stressed palms were infested with R. cruentatus , compared with none of the five undisturbed palms within 84 to 112 d. These data suggest that R. cruentatus is a secondary invader of stressed or dying palms and not a threat to healthy palms. Propoxur (70% wettable powder [WP], 21.0 g [All/liter); chlorpyrifos (50% WP, 1.2 g [AI]/liter); lindane (25% WP, 0.6 g[AI]/liter); dimethoate (0.49 kg/liter emulsifiable concentrate [EC], 1.2 g [AI]/liter) and methomyl (90% WP, 1.0 g [AI]/liter) killed R. cruentatus adults in a bioassay done with pineapple tops, although methomyl failed to produce 100% mortality after 168 h. The mean time to mortality for R. cruentatus was <24 h for chlorpyrifos, propoxur, and lindane and 42 h for dimethoate. Prophylactic insecticide treatment applied to palms before transplanting is recommended for control of attacking weevils.