E. David Morgan

The specialist digger wasp Trachypus boharti Rubio‐Espina preys exclusively on males of the stingless bee Scaptotrigona postica Latreille 1807, although the hunting attacks involve both male and worker bees of S. postica and members of its own species. To understand the mechanism of prey selection, the cuticular hydrocarbon patterns of workers and males of S. postica are analyzed in detail, and the mandibular secretion of males is examined. The cuticular profiles of males and workers are distinctively different. The major group of cuticular compounds, heptacosene isomers, is twice as abundant in workers as in males. There is no clear distinction between worker and male mandibular secretions. Such a distinct and straightforward caste‐specific difference in cuticular hydrocarbons could function as a recognition cue by which T. boharti distinguishes between workers and males of S. postica .

The study of trail laying, recruitment of workers and trail‐following by worker ants comprises a co‐operative study of entomologists and chemists that has resulted in the identification of the chemical nature of such pheromones in many species of five subfamilies of ants. These pheromones may comprise a single compound or, in one exceptional case, a blend of as many as 14 compounds, they may come from a single gland, or in some cases, a combination of two glands. They may be peculiar to a single species or may be shared by a number of species. They exist in the glandular secretion in nanogram to picogram quantities and are detected by workers in minute amounts on a trail. The present state of knowledge of these pheromones and their chemical structures is reviewed. Suitable bioassays and odour perception are discussed and the stereobiology of a few examples is considered.

The effects of the natural compound 2‐methoxy‐1,4‐naphthoquinone, isolated from the leaves of Impatiens glandulifera and the synthetic compounds 2‐propoxy‐1,4‐naphthoquinone and 2‐isopropoxy‐1,4‐naphthoquinone on ecdysone 20‐monooxygenase (E‐20‐M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabelled ecdysone and increasing concentrations (from 1 × 10^–8 to 1 × 10^–3 M) of the three compounds. All three compounds were found to inhibit in a dose‐dependent fashion the E‐20‐M activity in the three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 3 × 10^–5 to 7 × 10^–4 M. Arch. Insect Biochem. Physiol. 66:45–52, 2007.

The secretion from the mandibular glands of males of the leaf‐cutting ant Atta sexdens rubropilosa is responsible for the reaction of workers outside the nest at the time of sexual swarming. Workers respond with excitability and aggression when presented with the natural mixture of 4‐methyl‐3‐heptanol and 4‐methyl‐3‐heptanone, which is contained in the secretion of the male mandibular glands. Workers respond quickly to fractional amounts of one male equivalent. 4‐Methyl‐3‐heptanone, from the virgin female mandibular glands causes much less response in workers, whereas an equimolar mixture of male and female pheromones gives a still less clear response. The male pheromone plays the most important part in the communication of workers outside the nest at this time.

The amount of the trail pheromone substance, 3-ethyl-2,5-dimethylpyrazine, of the leaf-cutting ant Atta sexdens sexdens (Hymenoptera: Formicidae) increases with increasing size of the ant from 0 to 35 ng per individual. The compounds 2,5-dimethylpyrazine and trimethylpyrazine are also consistently present. Trails of venom gland extracts are followed with unequal fidelity by different castes. Minor workers follow best, mediums least well. Workers walk sinuously on narrow trails and less sinuously on wider trails up to 9 mm. Trails wider than 9 mm are not followed. The optimum concentration of pheromone on synthetic trails lies between 15 and 150 pg cm^-1. Given a choice of concentrations at a trail branch, workers always choose the more concentrated. Workers showed slight preference for a trail made with venom gland secretion from their own, over that from an alien colony, but there is no preference for a trail that contains Dufour gland secretion additionally.