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- Bionomics of the Cotton Flowerweevil, Amorphoidea Lata Motschulsky...
Bionomics of the Cotton Flowerweevil, Amorphoidea Lata Motschulsky (Coleoptera: curcullonidae)
Thesis Abstract:
The study confirmed that all Amorphoidea populations in the Philippines belong to only one species but they showed considerable geographical variation from Luzon to Mindanao. The life cycle of the cotton flowerweevil, A. lata Motschulsky, was completed in 10.06 to 16.83 days. Eggs were laid singly at the base of the petals/ovary sheath and hatched within 1.40 to 3.54 days. The larval stage ranged from 5.66 to 7.86 days with two distinct periods (feeding and resting/pre-pupal period). The pre-pupal and pupal stages lasted 2.28 to 3.25 and 3.0 to 5.43 days, respective ly. Adults emerged during the day, with the peak of emergence between I 0:00a.m. to II :00 a.m. Newly emerged adults did not mate but fed within 5 to 64 minutes and were active flyers. A. lata was observed in the different cotton growing areas of the country. During the 1989-90 cotton season, its distribution and abundance were reported in 10 cotton growing provinces, being present throughout the tlowering period of cotton.
Adult flowerweevils preferred to feed on petals rather than on stigma and anthers. Both adults and larvae inflicted injuries on cotton flowers/young bolls. Injuries caused by adults were through feeding and egg deposition on the flower, while larval feeding on the ovaries/young bolls resulted in premature shedding of young bolls. Friedman's ranked test showed no significant ovipositional preference among the varieties tested, which indicated that female weevils laid their eggs on any cotton variety.
Based on tlower/boll infestation records, percent damage was relatively high in llocos Norte, Cagayan, and Pangasinan. The peak of infestation was recorded from January to March and the lowest was in December. The peaks oflarval and adult populations were also registered from January to March. Seasonal fluctuations in flowerweevil population and infestation were influenced by the main and interaction effects of relative humidity, temperature, and solar rad iation at a given number of days after emergence during October, November, and December 1989 plantings, respectively.
The role of alternate host plants on the survival of cotton flowerweevils, especially during cotton off-season, was found to be important. Among the reported host plants, okra and balibagu tree were found to be the source offood in the absence of cotton. Four species of insect predators were observed to prey on adults and immature stages of the flowerweevil. Geocorisjlaviceps (Burmeister) and G. ochropterus (Fieber) attacked adults, while Solenopsis geminata (Fabr.) and Euborellia annulata (Fabricius) were found to attack those in immature stages. Predation by these species was considered as key mortality factor in the field.