A three-year (1991-1993) investigation was done in the field and laboratory to study the bionomics of Smicronyx guineanus Voss and Sm. umbrinus Hustache and the spatial distribution of Striga hermonthica (Del.) Benth. Studies on the life history of the weevils were undertaken. Seasonal activity and habits were established by monitoring life stages in the field. A behavioral Time Budget of Smicronyx adults was established in semi-field conditions. Dispersion patterns and the optimum sample size for Smicronyx and Striga were determined. Smicronyx adults as well as Striga plants were aggregated in the field. Smicronyx larvae were located in the upper stratum of the witchweed (93.2%) where they make galls and destroy large number of seeds. The effect of precipitation on emergence of Smicronyx adults was investigated in the insectary. The optimum rainfall required for Smicronyx adult emergence ranged from 30 to 40 mm. Good synchrony and positive association of Sm. guineanus and Sm. umbrinus with S. hermonthica were observed. There are good prospects for augmentation and/or conservation of Smicronyx populations as part of an integrated control strategy of S. hermonthica.

No description available.

The potential of Smicronyx umbrinus Hustache and Smicronyx guineanus Voss (Coleoptera: Curculionidae) as biocontrol agents of Striga hermonthica (Del) Benth was investigated at both population levels of Striga and Smicronyx spp. in the field in Burkina Faso. High population levels of Smicronyx spp. resulted in higher percentages of seed-pod galls although the weevils' adult populations decreased during S. hermonthica seed capsule production. Smicronyx spp. were observed galling Striga aspera (Willd) Benth capsules ca. 60 days before S. hermonthica emerged in sorghum fields. The weevils also galled S. hermonthica stems at soil level and Sm. umbrinus was found to be the main species causing this symptom. Smicronyx spp. also galled Alectra vogelii Benth stems, Smicronyx dorsomaculatus Cox being the main species attacking this parasitic weed. Another Smicronyx species not yet described was collected on A. vogelii. Stem galls appeared to be more effective nutrient sinks than fruit galls. The weevils alone did not have sufficient impact to be considered successful biocontrol agents for S. hermonthica but they could contribute to an integrated control strategy against Striga. Smicronyx spp. have a good potential as biocontrol agents for A. vogelii.

No description available.