Astrid T. GROOT, Antje SCHUURMAN, J. Hans VISSER & Leo H.M. BLOMMERS
Research Institute for Plant Protection (IPO-DLO), Binnenhaven 5, P.O.
Box 9060, 6700 GW Wageningen, The Netherlands
The green capsid bug Lygocoris pabulinus (L.) is a serious pest in apple orchards and various other crops (1); low population densities can cause considerable damage (2). Adult males are attracted to virgin-female-baited traps in the field, indicating that females may emit a sex pheromone (2). Our aim is to elucidate this pheromone, which will enable pest monitoring at an early stage or may be used for mating disruption.
Mating experiments showed that L. pabulinus is reproductively mature when 6 days old (3). With reproductively mature bugs we conducted olfactory bioassays in no-choice situations, using glass cylinders of 50 cm long with a diameter of 11 cm (see 3). About 50% of the males flew or walked upwind towards virgin females on a potato leaf, whereas virtually no males responded when nothing was offered upwind. After removal of the females the leaf still elicited about 50% response, while only about 12% of the males responded towards females alone. The response towards females plus potato leaf is partly due to the leaf itself; about 15% of the males responded towards mechanically damaged potato leaf. Therefore we conducted a new series of experiments under the same conditions, but now using goosefoot leaf instead of potato leaf. Only 5 of the tested males responded towards mechanically damaged goosefoot leaf, 72 did not respond at all. The overall response of males towards females plus goosefoot leaf was about 35%. The combination of females plus leaf appears to have a synergistic effect; the response towards females alone added to the response of infested leaf alone gives a lower result.
The low response towards females alone, however, may result from the females lacking food or moisture supply; in such conditions the bugs dessicate completely in three hours. This problem was solved by the addition of a little glasstube filled with water to the dish with females. On such tubes females can survive for two to three days. The male response towards these females was about twice as high as towards females alone, whereas no response was observed towards the glasstube alone.
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