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 spect roscopy technique. Both male and female secretions consisted of two ma jor components: (E)-2-octenal and n-octyl acetate, 76 % and 16 % (w/w) , respectively. The remaining 8% were trace compounds, some of which w ere identified as hexyl acetate, 3-octenal, 1-octanol, and (Z)-3-octen yl acetate. In a survey among 38 coreid defensive secretions, (E)-2-oc tenal and n-octyl acetate were found to occur rarely in addition to co reid-specific compounds, while their combination as primary constituen ts was found to be unique. Toxicity and repellency of this secretion w ere evaluated using two household pests, Anoplolepis longipes and Sito troga cerealella, as test insects, and lethal concentration (LC50) val ues of 0.24 ppm and 0. 14 ppm, respectively, and repellencies of 63% a nd 58%, respectively, were obtained. Comparing the above values with t hose of a pentatomid bug, Coridius janus, evaluated under the same con ditions, it was apparent that this secretion has potential as a repell ent to enemies of L. oratorius but not as a toxicant to attack them. B ioassay on the alarm activity of this secretion revealed that it elici ts alarm responses, alerting and dispersing aggregated male and female L. oratorius: this is followed by ''self-coating'' activities. In add ition, some unique behaviors were also noted among alarmed L oratorius .