Benzoquinone levels as a function of age and gender of the red flour beetle, Tribolium castaneum

Liquid chromatography with both photodiode array and electrochemical detect ion was used to analyze as a function of age and gender the levels of two r ho-quinones, methyl-1,4-benzoquinone (MBQ) and ethyl-1,4-benzoquinone (EBQ) , which are found in defensive secretions of the red flour beetle, Triboliu m castaneum. We developed a method to simultaneously analyze quinones and h ydroquinones excreted from or in homogenates of individual beetles. The maj or components present in beetle extracts were the benzoquinones and not fre e or conjugated forms of the hydroquinones. Greater than 95% of the quinone /hydroquinone mixture in extracts was present in the oxidized form. Because of their lability, however, the quinones were quantified indirectly as the ir hydroquinone derivatives after extraction in dilute acid supplemented wi th ascorbic acid as a reducing agent. Comparisons of whole body rinses and homogenates revealed that rinses recovered only up to 60% of the total quin ones that were extracted after homogenization. The levels recovered also de pended on the age and sex of the individual beetles sampled. rho-Benzoquino nes in both male and female beetles increased after adult eclosion and cuti cle sclerotization for 40-50 days and then remained at their highest levels (15-21 mu g MBQ and 22-32 mu g EBQ per beetle) through 80 days posteclosio n. Virgin females that were collected 40-80 days after eclosion contained a pproximately 40% more of these compounds than males of the same age. The bu ild-up of rho-benzoquinones subsequent to cuticle sclerotization apparently reflects the need for an adequate cuticular barrier for self-protection fr om these defensive compounds. (C) 1998 Elsevier Science Ltd. All rights res erved.