Responses of Diaphorina citri Kuw. (Hemiptera: Liviidae) to mixtures of β-ocimene, d-limonene and methyl salicylate, under controlled conditions

Some pathogens can alter the quantity and quality of volatiles produced by their host plants. This change in the volatile profile can result in an enhanced attraction of vector insects, which may favor the pathogen's dispersion. There is evidence that HLB-diseased plants present changes in their volatile profile composition, and they result more attractive to Diaphorina citri Kuw. (Hemiptera: Liviidae) than healthy plants. D-limonene and methyl salicylate were two of the compounds that had a significant increase in diseased plants, which could explain its attractiveness. For this reason, we tested the response of D. citri to mixtures of four different compounds using a Y-tube olfactometer. The highest attraction was to d-limonene at a concentration of 100 µg (Χ²= 11.16; df= 1; P < 0.001), to 100 µg of (Z) β-ocimene alone (Χ²= 19.88, df= 1, P < 0.001) and to the combination of 100 µg of (Z) β-ocimene and 100 µg of d-limonene (Χ²= 13.90226; df= 1; P < 0.001). Methyl salicylate at a concentration of 0.01 μl had a strong repellent response (Χ²=28; df= 1; P < 001). (E) β-ocimene alone was not more attractive than control (Χ²= 1; df= 1; P = 0.179), but the addition of (E) β-ocimene to (Z) β-ocimene strongly inhibited the attractiveness of the latter (Χ²= 3.085, df= 1; P= 0.079). The results indicate that some of the compounds have inhibitory or synergistic effects when they are alone or in combination.

Key words:  Bioassay, olfactometer, volatiles, inhibition