The Production of Sex Pheromone in Lady Beetles Is Conditioned by Presence of Aphids and Not by Mating Status

Female Harmonia axyridis (Coleoptera: Coccinellidae) produce a sex pheromone to attract males. In the present study, we tested
two hypotheses: (i) production of sex pheromone in H. axyridis is conditioned by perception of prey in their vicinity, and (ii)
virgin females invest in the production of the sex pheromone, while mated females reduce their pheromone emissions. To test the
first hypothesis, newly hatched larvae were divided into three groups: those fed with Ephestia kuehniella eggs, those fed with pea
aphids, and those exposed to aphid volatile cues but fed with Ephestia eggs. All females produced a pheromone blend of fivecomponents
in similar relative proportions, but with contrasting absolute quantities: Females fed with Ephestia eggs produced
lower amounts of pheromone (0.5 ± 0.4 ng.female−1), compared to females fed with aphids (44.2 ± 24.4 ng.female−1). The
females of the third group produced intermediate concentrations of pheromone (6.0 ± 3.2 ng.female−1). To test the second
hypothesis, two groups of lady beetles were made: one group of females was placed in the presence of males, while females
of the other group were not.Mated and virgin females produced statistically similar amounts of pheromone (144.1 ± 49.7 ng and
43.7 ± 24.1 ng.female−1, respectively). These results suggest that H. axyridis females initiate pheromone production upon
exposure to volatile cues released by their aphids prey. Females continue to release sex pheromone after mating, probably to
increase the chance of multiple mating which is known to improve egg fertility.