Bean Type Modifies Larval Competition in Zabrotes subfasciatus (Chrysomelidae: Bruchinae).

Larval competition is particularly prevalent among grain beetles that remain within their mother-selected grain throughout development, and the behavioral process of competition is usually inferred by the competition outcome. The Mexican bean weevil Zabrotes subfasciatus (Boheman) is subjected to resource availability variation because of the diversity of common bean types and sizes, from small (e.g., kidney beans) to large (e.g., cranberry beans). The competition process was identified in the Mexican bean weevil reared on kidney and cranberry beans by inference from the competition outcome and by direct observation through digital X-ray imaging. Increased larval density negatively affected adult emergence in kidney beans and reduced adult body mass in both kidney and cranberry beans. Developmental time was faster in cranberry beans. The results allowed for increased larval fitness (i.e., higher larval biomass produced per grain), with larval density reaching a maximum plateau >5 hatched larvae per kidney bean, whereas in cranberry beans, larval fitness linearly increased with density to 13 hatched larvae per bean. These results, together with X-ray imaging without evidence of direct aggressive interaction among larvae, indicate scramble competition, with multiple larvae emerging per grain. However, higher reproductive output was detected for adults from lower density competition with better performance on cranberry beans. Larger populations and fitter adults are expected in intermediate larval densities primarily in cranberry beans where grain losses should be greater.

Cage and field assessments of Beauveria bassiana-based Mycoinsecticides for Myzus persicae Sulzer (Hemiptera: Aphididae) control in cabbage.

The efficiency of formulated Beauveria bassiana-based mycoinsecticides to control Myzus persicae (Sulzer) in cabbage was assessed under field conditions. Aqueous conidial suspensions (0.01% Tween 80 + 0.01% v/v Agral) of three fungal isolates were sprayed twice at different dates, each with 2.0 x 10(9) viable conidia per potted plant using screened cages. The number of nymphs and adults of M. persicae per leaf was significantly reduced in plots treated with isolates CG 864 and PL 63, with control efficiency ranging from 57% to 60%. Further field trials using screened cages with isolate CG 864 formulated as oil dispersion reduced the aphid population by 85-87% as compared to the control, whereas a 71% reduction was seen in plants treated with the aqueous conidial suspension 20 days following the first spray. The last experiment was conducted in a commercial cabbage field (without cages), in which the fungus was applied at three different dates, each with an equivalent of 1.0 x 10(13) viable conidia/ha. The reduction in the number of aphids per leaf was more evident between four and five weeks following the first spray, resulting in 76-83% and 57-65% control efficiency for oil dispersions and unformulated conidia, respectively. However, with the exception of imidacloprid-treated plants, rapid aphid re-infestation was observed in all treatments. In this study, the stand-alone use of mycoinsecticides for aphid control was not a satisfactory strategy, although utilization of B. bassiana in IPM strategies remains a field to be explored.