Female sex pheromone in the rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae): Its identification and its use for control

The rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), is one of the major pests causing pecky rice, and its control is necessary. A new monitoring system needs to replace the laborious net sweeping. In this study, it was confirmed that male adults were attracted to a trap with adult females of T. caelestialium, indicating that a female sex pheromone is produced, as reported in other mirid species. The female sex pheromone was analyzed by Coupled Gas Chromatography-Electroantennographic Detection (GC-EAD) and its effectiveness was confirmed by field attraction tests using synthetic sex pheromone candidates. The main sex pheromone components were identified as n-hexyl n-hexanoate (H:H) and (E)-2-hexenyl n-hexanoate (E2H:H). The addition of n-octyl n-butyrate (O:B) to these compounds was shown to enhance the attraction of males. A mixture of H:H, E2H:H and O:B in the ratio of 1000: 400-500: 10-100 demonstrated high attraction activity. Only male adults were attracted to the mixture of these three components, just as females attracted only conspecific males, and not females. Traps containing a mixture of these three synthetic sex pheromone components in a ratio of 100: 40: 3 were shown to attract males in numbers equal to or higher than traps with two females of the bug. Trials on mating disruption demonstrated that treatment with the 3-component sex pheromone (H:H, E2H:H and O:B) disturbed the copulation of T. caelestialium adults and consequently reduced their reproduction under laboratory conditions. Experiments in a 100-square m field revealed that the 3-component sex pheromone interfered with male attraction to traps baited with either the lure or with three adult females. Application of the 3-component sex pheromone in a 1-ha (10,000-square m) field indicated a continuous effect on the inhibition of attraction towards the trap, resulting in decreased T. caelestialium population densities to 22-45% for adults and 0-2% for nymphs, in comparison with untreated fields, based on sweep-net samplings. Hence, the option of control by communication disruption using the sex pheromone appears viable. As a possible alternative to sweep-net sampling of vegetation in and around paddy fields, the potential for using pheromone-baited traps for monitoring of T. caelestialium was effective. To elucidate the mechanism of mating disruption, it will be necessary to study the minimum field size for treatment, dispenser density, method of dispenser placement and the protective effect against pecky rice in paddy fields and also against infestation of other crops. Finally, the elucidation of the sex pheromone of T. caelestialium has enhanced the possibility of developing new monitoring tools, bringing closer the bug's control in an environmentally safe manner, without the use of pesticides.