Recruitment and retention of predatory coccinellid beetle, Cheilomenes sexmaculata (Fab.) using synthetic semiochemicals

The six-spotted zigzag ladybird beetle, Cheilomenes sexmaculata (Coleoptera: Coccinellidae), is a prevalent generalist predator in India, commonly observed on maize and wheat during the summer and winter seasons. Ladybird beetles are important natural predators of aphids and other sap-sucking pests in maize and wheat crop ecosystems. Enhancing their abundance in the field through attractants is essential for the success of augmentative biological pest control programmes. This study aimed to evaluate the effectiveness of eight synthetic volatiles in attracting ladybird beetles using electroantennogram tests, olfactometer bioassays, and semi-field and field trials. In EAG studies, benzaldehyde and terpineol significantly triggered responses in adult males and females without any significant difference between the sexes. In dose-dependent olfactometer bioassays, at five doses (10 μg, 100 μg, 300 μg, 700 μg, and 1000 μg), C. sexmaculata adults exhibited a preference for 700 μg of benzaldehyde (74.28%) and terpineol (72.62%) over other doses. However, none of the twelve blends of these two attractive compounds showed a significant attraction to C. sexmaculata. Subsequently, all these eight synthetic semiochemicals were evaluated for ladybird beetle attraction in semi-field and field trials over different weeks. Terpineol (50.20 ± 0.31), benzaldehyde (41.67 ± 0.35), and (+)-3-carene (27.73 ± 0.33) were confirmed as attractants in semi-field trials over 3 weeks, and the same trend was noticed in the field trials over the 8 weeks. However, the attraction patterns in the field trails varied slightly between grubs and adults regarding (+)-3-carene and methyl salicylate. While adults clearly preferred (+)-3-carene over methyl salicylate, grubs showed no significant difference in attraction to these two compounds. This study lays the groundwork for developing optimal attractant formulations for C. sexmaculata, potentially enhancing the biocontrol services of this predator in its native area, such as India.