Acceptance and utilization efficiency of a purple durum wheat genotype by Sitophilus granarius (L.)

The granary weevil, Sitophilus granarius (Coleoptera, Curculionide) is one of the most damaging primary pest of stored cereals worldwide. Flavonoids are a major class of secondary plant metabolites which modulate feeding response and growth rate in insects. In the present study, the susceptibility to the granary weevil of the durum wheat T1303, an anthocyanin-rich purple genotype, in comparison with the yellow commercial durum (Ofanto) and bread (Mec) wheat varieties was evaluated. Moreover, to investigate the feeding response and food utilisation efficiency by adult insects, nutritional indices were calculated by means of flour disk bioassays. The total number of F1 progeny, the female parental offspring, and mean food consumption by an insect recorder for the T1303 genotype were significantly lower compared to yellow wheat varieties indicating different level of susceptibility to S. granarius attacks. Actually, T1303 induced positive values of Food Deterrence Index (FDI) indicating deterrence. Besides, Relative Grow Rate (RGR) and Efficiency Conversion of Ingested Food (ECI) indices were negative for T1303 and positive for both yellow wheat varieties indicating a decrease and an increase of insect body weight during the experiment, respectively. Finally, adult mortality of insects fed on T1303 whole flour disks was significantly higher than those observed for insects feed on yellow wheat varieties after six-day exposure. These results strongly suggested antifeedant and toxic effects of anthocyanins accumulated in the pericarp of T1303 kernels against granary weevils offering new insights into the mechanism of host acceptance and food utilization by this pest. This information would be useful to identify antifeedant flavonoids as well as in breeding programs aimed at developing varietal resistance-based strategies against stored-product insect pests.