DEFENSIVE SECRETION OF RICE BUG, LEPTOCORISA-ORATORIUS FABRICIUS, (HEMIPTERA, COREIDAE) - A UNIQUE CHEMICAL-COMBINATION AND ITS TOXIC, REPELLENT, AND ALARM PROPERTIES

Defensive secretion produced by adult males and females of Leptocorisa oratorius, Fabricius (Hemiptera: Coreidae) living on the host plant, Oriza sativa, was analyzed by a combined gas chromatography-mass spectroscopy technique. Both male and female secretions consisted of two major components: (E)-2-octenal and n-octyl acetate, 76 % and 16 % (w/w), respectively. The remaining 8% were trace compounds, some of which were identified as hexyl acetate, 3-octenal, 1-octanol, and (Z)-3-octenyl acetate. In a survey among 38 coreid defensive secretions, (E)-2-octenal and n-octyl acetate were found to occur rarely in addition to coreid-specific compounds, while their combination as primary constituents was found to be unique. Toxicity and repellency of this secretion were evaluated using two household pests, Anoplolepis longipes and Sitotroga cerealella, as test insects, and lethal concentration (LC50) values of 0.24 ppm and 0. 14 ppm, respectively, and repellencies of 63% and 58%, respectively, were obtained. Comparing the above values with those of a pentatomid bug, Coridius janus, evaluated under the same conditions, it was apparent that this secretion has potential as a repellent to enemies of L. oratorius but not as a toxicant to attack them. Bioassay on the alarm activity of this secretion revealed that it elicits alarm responses, alerting and dispersing aggregated male and female L. oratorius: this is followed by ''self-coating'' activities. In addition, some unique behaviors were also noted among alarmed L oratorius.