Stimoli chimici nelle interazioni tra individui di Ceratomegilla undecimnotata (Schneider) (Coleoptera Coccinellidae) in fase di aggregazione

Chemical stimuli involved in interactions among individuals of Ceratomegilla undecimnotata (Schneider) (Coleoptera Coccinellidae) in aggregations. - Among Coccinellids, Ceratomegilla (=Semiadalia) undecimnotata is one of the most studied species because it migrates in large numbers towards overwintering sites (located both in hill or mountain) before diapausing. In this paper the results of bioassays carried out both in two-way olfactometer and arena are reported, in order to show the possible role of volatile and non volatile chemicals on such species. In all the experiments aggregating individuals of C. undecimnotata, collected from overwintering sites located either in France or Italy, have been used. In the olfactometer bioassays we evaluated the amount of time spent in each of the two arms; one arm was injected with pure air, while the other was injected with pure air passing through an aggregation of males or females. In arena three set of experiments have been performed. In the first two an heptane extract of both sexes C. undecimnotata elytra was applied either on glass and paper. In the third experiment the elytra were used as a dummy after having been washed with solvents characterised by different polarity. In all bioassays the behaviour of single individuals was observed for the described treatments, evaluating the time spent in the treated arena and the number of individuals that showed arrestment on the same arena. Data analysis showed that in olfactometer females spent a significantly lower time in the arm with aggregated males. In the arena bioassays males spent a longer time over the glass slide treated with male elytra extract, while in the paper experiments a lower number of females showed arrestment over the female extract treated areas. In the dummy experiments, a higher number of females were found over elytra treated with alcohol compared with those washed with chloroform and with those unwashed. Although these results are preliminary and will need more research, it is possible to show, for the first time in this species, how chemical stimuli can play a role in the interaction among aggregating individuals.