Attractiveness of male azuki bean beetle to the synthetic blends of 2E- and 2Z-homofarnesals

Abstract

Use of synthetic pheromones is biologically and economically effective approach in insect pest management programs. The female adults of azuki bean beetle (Callosobruchus chinensis L.), a worldwide oligophagous pest of legumes including azuki beans, produce sex pheromone components known as homofarnesals with two isomer compounds; (2Z,6E)-7-ethyl-3,11-dimethyl-2,6,10-dodecatrienal (2Z-homofarnesal) and (2E,6E)-7-ethyl-3,11-dimethyl-2,6,10-dodecatrienal (2E-homofarnesal). We used Z-selective method to synthesize 6:4 blend of 2E- and 2Z-homofarnesal and compared its attractiveness with two other blends; 9:1 and 1:9 using Y-olfactometry in laboratory and rocket traps in the field. Both laboratory and field experiments ascertained the higher attractiveness of synthetic homofarnesal with higher proportion of 2Z-homofarnesal. Among the tested blends of 9:1, 6:4 and 1:9 of 2E- and 2Z-homofarnesal in Y-olfactometry, the attractiveness pattern was found as 1:9≥6:4>9:1 blend. Under field condition also, the 6:4 blend was more attractive with the recapturing efficiency of 31.4±2.6% as compared to 13.6±0.4% of 9:1 blend of 2E-:2Z-homofarnesal. The result of this experiment provides an opportunity to synthesize pheromone rich in 2Z-homofarnesals with less sophisticated and economically feasible Z-selective method to incorporate it in eco-friendly alternative of azuki bean beetle management.