Methoprene modulates the effect of diet on male melon fly, Bactrocera cucurbitae, performance at mating aggregations

The effect of access to dietary protein (P) (hydrolyzed yeast) and/or treatment with a juvenile hormone analogue, methoprene (M), (in addition to sugar and water) on male aggregation (lekking) behaviour and mating success was studied in a laboratory strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Six-day-old males were treated with (1) protein and methoprene (M+P+), (2) only protein (M-P+), or (3) only methoprene (M+P-), and compared with 14-day-old sexually mature untreated males (M-P-). The lekking behaviour of the four groups of males when competing for virgin sexually mature females (14 -16 days old) was observed in field cages. The following parameters were measured at male aggregations: lek initiation, lek participation, males calling, male-male interaction, female acceptance index, and mating success. For all these parameters, the M+P+ males significantly outperformed the other males. Moreover, for all parameters, there was a similar trend with M+P+ > M-P+ > M-P- > M+P-. More M+P+ males called and initiated and participated in lek activities than all other types of male, which resulted in higher mating success. They had also fewer unsuccessful copulation attempts than their counterparts. Whereas treatment with methoprene alone had a negative effect in young males with only access to sugar, access to dietary protein alone significantly improved young male sexual performance; moreover, the provision of methoprene together with protein had a synergistic effect, improving further male performance at leks. The results are of great relevance for enhancing the application of the sterile insect technique (SIT) against this pest species. The fact that access to dietary protein and treatment of sterile males with methoprene improves mating success means that SIT cost-effectiveness is increased, as more released males survive to sexual maturity.