Volatile secretions of Ulomoides dermestoides (Coleoptera: Tenebrionidae): Toxic effects on human cells. Markers of beetle fitness.

JUÁREZ M. PATRICIA; CRESPO ROSANA; VILLAVERDE LUCIANA M; GARCÍA DE BRAVO MARGARITA; GIROTTI JUAN R

Greenwich

Congreso; Ento´11. Royal Entomological Society's Annual National Meeting e International Symposium on Chemical Ecology: Reception, Detection and Deception.; 2011

Royal entomological Society

The Oriental tenebrionid Ulomoides dermestoides was introduced in Argentina as alternative medicine for treatment of cancer and respiratory diseases. However, after unrestrained use of this beetle, it has already been detected infesting stored wheat grain facilities. The major components of the beetle defensive volatile blend are methyl-1,4-benzoquinone (MBQ), ethyl-1,4-benzoquinone (EBQ) and 1-pentadecene (C15:1) [1]. The aim of this study was to investigate the toxic effects of this volatile organic compounds (VOC) on human cells. Additionally, we evaluated the effect of entomopathogenic fungal infection on beetle’s volatile secretions and colony fitness. Insect VOC were tested for their toxicity against human lung carcinoma epithelial cell line A549. Cytotoxicity was demonstrated by MTT (3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test and Trypan blue assay, genotoxicity was evaluated by the comet assay. Synthetic 1, 4-benzoquinone (BQ) and C15:1 were also tested in A549 cells and normal mononuclear human cells. To evaluate the relationship between VOC release and insect health, beetles were immersed in a suspension of a commercial strain of Beauveria bassiana (GHA) (1 × 109 conidia/ml, for 6 s). The VOC released by infected and healthy beetles were compared by head space-solid phase microextraction (HS-SPME) coupled to capillary gas chromatography (CGC). We also compared the effect of fungal infection on colony development. Beetle VOC showed cytotoxic activity on human A549 cells, with half maximal inhibitory concentration (IC50) values of 0.26 (MTT test) and 0.34 equivalent/ml (Trypan blue assay), respectively. The synthetic blend (BQ and C15:1) or BQ alone, produced  similar inhibition values; C15:1 showed no inhibitory effect. Low doses of insect extract or synthetic blend (0. 15 eq/ml) inhibited mononuclear cell proliferation by 72.2 ± 2.7 % and induced significant DNA damage both in tumor and mononuclear cells [3]. Thus, insect benzoquinones are primarily responsible for inducing cytotoxicity and genotoxicity in culture cells. The relative amount of the volatile blend components was unaffected by fungal infection; although 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 [2]. These results suggest that after the infection takes place -regardless actual mortality values- the insect behavior might be altered because they are unable to get rid of these toxic secretions. Because these compounds function as repellents or deterrents to other insects, diminished secretion of defensive compounds might provide a physiologic clue for behavioral changes in infected beetles that could strongly alter their life cycle.   [1] Villaverde M.L. et al. Comp Biochem Phys B 2009, 154: 381–386. [2] Pedrini N. et al. J Econ Entomol 2010, 103(4): 1094-1099. [3] Crespo R. et al. J Ethnopharmacol 2011(in press)