Olfactory responses of seed wasps Megastigmus pinus parfitt and Megastigmus rafni Hoffmeyer (Hym., Torymidae) to host-tree odours and some monoterpenes.
Megastigmus pinus and Megastigmus rafni are able to colonize the seed cones in eight different species of Abies in Denmark. Olfactory responses of M. pinus females from Abies alba and Abies procera seeds and of M. rafni females from A. alba and Abies grandis seeds to odours of different host-trees cones, needles and pure alpha-pinene and limonene were studied in a Y tube Plexiglas olfactometer. The odours of young cones significantly influenced the behaviour of females. The results obtained in experiments with cones from different trees indicate the occurrence of biotypes depending on the host tree within the M. pinus and M. rafni species. Megastigmus pinus females from A. procera cones preferred the cone odours of A. procera and were significantly repelled by the cone odours of other possible host trees. Megastigmus pinus females from A. alba cones preferred A. alba cone odour but were not indifferent to A. procera cones. This suggests that the M. pinus population in A. alba apparently originates from the A. procera population. Megastigmus rafni from A. grandis cones preferred only A. grandis cone odours. Megastigmus rafni females from A. alba cones preferred A. alba cone odour but were also significantly attracted by A. grandis cone odours. This probably indicates that the M. rafni population living in A. alba originates from the A. grandis population. Neither M. pinus nor M. rafni responded to the odours of the host-tree needles or alpha-pinene. The limonene odour significantly acted as a repellent to both seed chalcid species, independent of the origin-tree.