Volatile secretions as chemical signals in Ulomoides dermestoides (Coleoptera: Tenebrionidae)

J.R. GIROTTI; M.L. VILLAVERDE; N. PEDRINI; S.J. MIJAILOVSKY; C.B. FUSÉ; M.P. JUÁREZ

Colonia del Sacramento

Congreso; 1st Latin American Meeting of Chemical Ecology; 2010

Latin American Association of Chemical Ecology

The Oriental tenebrionid Ulomoides dermestoides has been introduced in the country as alternative medicine for treatment of cancer and respiratory diseases. Unrestrained use of this beetle led to its dispersal and it has been detected infesting stored wheat grains in Argentina. We investigated the effect of entomopathogenic fungal infection on beetle’s colony fitness and chemical signals. The volatile organic compounds (VOC) released by U. dermestoides males and females separately set in sealed vials were analyzed by head space solid phase microextraction (HS-SPME) coupled to capillary gas chromatography-mass spectrometry (CGC–MS). We also used CGC–MS to analyze their epicuticular hydrocarbons. The effect of entomopathogenic fungal infection on VOC secretion and on colony development after insect immersion for 6 s in a suspension of Beauveria bassiana strain GHA (1 × 109 conidia/ml) was also studied. A pattern similar to that reported in other tenebrionids was detected [1]. Methyl-1,4-benzoquinone (MBQ), ethyl-1,4-benzoquinone (EBQ), 1-pentadecene (C15:1) and 1-tridecene (C13:1) were the major components of the volatile blend (> 90%); no sex dimorphism was detected. However, when insects were let walk on papers, HS-SPME analyses of the papers showed terpenoid-like components in males but not in females, in addition to the other VOC. These papers were only attractive to females in a two-choice experimental arena.  After fungal infection, the relative amount of each component was unaltered, but the total amount of volatile secretion dropped to 5% of that detected in healthy beetles. The development of the infected colony was strongly altered 3 months after treatment with B. bassiana, showing a significant reduction in insect progeny. These results suggest that after infection events take place, diminished amounts of defense secretion may be a physiologic clue for behavioral changes in infected beetles. In addition to the large amounts of hydrocarbons in the VOC, saturated, unsaturated, and branched structures with chain lengths ranging from 13 to 43 carbons were also detected. n-pentacosane (C25:0) and 9,11-pentacosadiene (9,11-C25:2) were the most abundant components, representing more than 40% of the cuticular hydrocarbons. No significant differences between males and females were detected in the major hydrocarbon components.