The bean bug,Riptortus clavatus lays scattered eggs (as opposed to the egg masses of pentatomids) on host as well as nonhost plants. Therefore, the first feeding stage (second-instar) nymphs emerging from eggs laid on nonhost plants need a signal that enables them to locate a food source at the lowest energy cost. Male-released (E)-2-hexenyl (E)-2-hexenoate, (E)-2-hexenyl (Z)-3-hexenoate, and myristyl isobutyrate play the double role of attractant pheromone for adults as well as aggregation pheromone, which enables the second-instar nymphs to find the host food plant. These male-specific semiochemicals are released only when foodstuff is available. On the other hand, females ofOoencyrtus nezarae, the most effective parasitoid of the host in Kumamoto, Japan (where the field experiments were conducted), utilize these semiochemicals as kairomones in order to locate the potential host community. Field experiments revealed that the synthetic pheromone rivaled 10 live males in the attraction of adults and second-instar nymphs. Captures of the egg parasitoidO. nezarae females in cylindrical sticky traps were significantly higher in traps baited with the synthetic semiochemicals than in control traps. The number of females captured was significantly higher than the number of males, although the captures in the sticky suction trap system revealed that the populations of male and female were not significantly different.

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We investigated the attraction of Riptortus clavatus to different component compositions of its aggregation pheromone (mixture of three components) in the field by the use of sticky traps. In two-component tests, each of (E)-2-hexenyl(E)-2-hexenoate (EE) and (E)-2-hexenyl(Z)-3-hexenoate (EZ) mixed with myristyl isobutyrate (MI) showed equally synergistic effects in attracting R. clavatus relative to MI alone. There was no correlation between the degree of attractiveness and the dosages of EE or EZ added to MI. No significant difference was observed in the numbers of insects caught between traps baited with the three-component blend (MIϩEEϩEZ) and traps with two-component blends (MIϩEE or MIϩEZ). In addition, two-component blends (MI : EE or MI : EZϭ2 : 1) were almost as attractive as the natural blend (MI : EE : EZϭ1 : 5 : 1), and even in the absence of the main component, EE. R. clavatus responded to a wide range of the pheromone component blends without a particular optimum blending ratio. This might characterize the aggregation pheromone of this bug.

Abstract:We investigated the effect of the feeding conditions of Riptortus clavatus (Thunberg) males on their attractiveness to conspecific individuals as part of a preliminary study to clarify the adaptive significance of the attraction. Males allowed to take food were found to attract a significantly larger number of conspecific adults than those not allowed. Moreover, males allowed to take food were found to have a significantly more developed fat bodies than those not allowed. The close relationship between the feeding conditions of Riptortus clavatus males and their release of attractants suggests that the attractants might play a key role in the food exploitation strategy of the bugs.

Abstract:To save labor for monitoring the occurrence of the bean bug Riptortus clavatus (Thunberg), we used automatic counting traps baited with synthetic attractants from July to December, 2004. This automatic counting trap utilizes a solar battery to work continuously and sends data automatically via a built-in mobile phone. The occurrence of the bugs was also monitored by three water-pan traps. The number of bugs counted automatically and the actual number of catches in the automatic counting trap were not always consistent. One of the reasons for this inconsistency might be due to that the current automatic counting trap could not eject clogged insects in a roller electrode. However, the number of seasonal catches by automatic counting and water-pan traps showed similar trends, and the catch numbers of these traps reached a peak around the same time, in October. Although the automatic counting trap needs improvement, it should be useful for investigating the occurrence of the bean bug population utilizing less labor.