Abstract
A study on the Biology of the palm weevil Rhabdoscelus maculatus was carried out at Tropiflora Ornamental Palm Nurseries in Sri Lanka. This weevil, an important pest of ornamental palms, was detected for the first time in Sri Lanka at Tropiflora Nurseries. Although the incidence of this weevil is restricted to ornamental palms at present, there is a potential threat of the weevil becoming a pest of important cultivations such as coconut and sugarcane. The present investigation was therefore, carried out to con-firm the identification of this weevil and to study its biology. The identification of the palm weevil was confirmed as R. maculatus Gyllenhal, 1838 and is the first record in Sri Lanka. Biological, morphological and behavioural aspects of the weevil were studied under laboratory, semi-natural and natural conditions. The adult is a small, reddish-brown weevil (10.38-12.62 mm in length) with two black markings on the elytra and two on the thorax. The female is slightly larger than the male. The rostrum of the female is longer and more curved than that of the male. The ventral surface of the rostrum is roughened in the male while it is smooth in the female. Adult weevils are nocturnal in habit and hide in plant sheaths and debris during the day. They fly only short distances at a time but flight during the day was not observed. Mature female lays eggs inside cavities made in the leaf sheath. Under laboratory conditions, the period for egg incubation is 5.00 + 0.82 d. The larva is creamy white and legless with a round, highly sclerotized, reddish brown head capsule. Larvae feed on stem tissues rapidly and make tunnels. The frequency distribution analysis of head capsule width revealed six larval instars. Early weevil infestation of palms is indicated by a jelly like substance oozing out of the holes in the leaf sheaths. R. maculatus larva takes about 7.75+ 3.70 weeks to complete its development and then pupate inside a cocoon made of tightly bound, fibrous material completing the pupal stage in 2.50 + 0.76 weeks. The total life cycle of this weevil is completed in 10-12 weeks. The life span of adult weevils is between 8-10 months under semi-natural conditions and four weevil generations per year occur under natural conditions. DOI: http://dx.doi.org/10.4038/tare.v14i3.4845 Tropical Agricultural Research & Extension 14(3): 2011 70-75
Highlights
Pests and diseases are a major constraint in ornamental palm nurseries in Sri Lanka
It is reported that Sugarcane (Saccharum officinarum) is the major host plant of R. obscurus, a similar pest found in New Guinea, Fiji, Australia and some other countries
In Guam, R. obscurus is a major pest of ornamental palms, betel nut palm (Areca catechu), coconut palm, (Cocos nucifera) and sugarcane, (Saccharum officinarum)
Summary
Pests and diseases are a major constraint in ornamental palm nurseries in Sri Lanka. It is reported that Sugarcane (Saccharum officinarum) is the major host plant of R. obscurus (cane weevil borer), a similar pest found in New Guinea, Fiji, Australia and some other countries. In Guam, R. obscurus is a major pest of ornamental palms, betel nut palm (Areca catechu), coconut palm, (Cocos nucifera) and sugarcane, (Saccharum officinarum). The most affected plants of R. obscurus are reported as coconut, betel nut, champagne palm (Hyophorbe lagenicaulis), pritchardia palm (Pritchardia pacifica), pygmy date palm (Phoenix roebelenii), Alexander palm, (Archontophoenix alexandrae), royal palm (Roystonea regia) and date palm (Phoenix canariensis). In Sri Lanka, the attack of R. maculatus is restricted only to ornamental palms in plant nurseries and has not so far become a pest of either coconut or sugarcane. The present investigation was carried out to confirm the identity of this pest and to study its biology and behavior under local conditions
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