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

Abstract

Liquid chromatography with both photodiode array and electrochemical detection was used to analyze as a function of age and gender the levels of two ρ-quinones, methyl-1,4-benzoquinone (MBQ) and ethyl-1,4-benzoquinone (EBQ), which are found in defensive secretions of the red flour beetle, Tribolium castaneum. We developed a method to simultaneously analyze quinones and hydroquinones excreted from or in homogenates of individual beetles. The major components present in beetle extracts were the benzoquinones and not free 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 their hydroquinone derivatives after extraction in dilute acid supplemented with ascorbic acid as a reducing agent. Comparisons of whole body rinses and homogenates revealed that rinses recovered only up to 60% of the total quinones that were extracted after homogenization. The levels recovered also depended on the age and sex of the individual beetles sampled. ρ-Benzoquinones in both male and female beetles increased after adult eclosion and cuticle sclerotization for 40–50 days and then remained at their highest levels (15–21 μg MBQ and 22–32 μg EBQ per beetle) through 80 days posteclosion. Virgin females that were collected 40–80 days after eclosion contained approximately 40% more of these compounds than males of the same age. The build-up of ρ-benzoquinones subsequent to cuticle sclerotization apparently reflects the need for an adequate cuticular barrier for self-protection from these defensive compounds.