Chemical attraction of fig volatiles to their pollinating fig wasps
榕果挥发物对传粉榕小蜂的吸引作用

The specificity of the relationship between fig species and their particular agaonine pollinators (Hymenoptera: Chalcidoidea Agaonidae) has long been regarded as the extreme example of co-evolution. The maintenance of the fig-fig wasp mutualism system is strongly dependent on the chemical orientation of pollinating fig wasps using fig volatiles. The pollinating fig wasps trace the fig volatiles of their particular host and enter the figs at receptive phase (female flower phase) only, where they oviposit for themselves or pollinate for their partners.Field assay and olfactometry experiments were designed to examine the chemical basis of the species-specific mutualism and the difference between receptive fig volatiles and non-receptive ones in attracting pollinators. Three tropical fig species: Ficus hispida, F.auriculata and F.semicordata, and their corresponding pollinating fig wasps Ceratosolen solmsi marchali, (C. emarginatus) and C.gravelyi were chosen for tests. Fig volatiles including 12 info-chemicals and 3 dichloromethane extracts of figs in receptive and inter-floral phases were tested. The field experiments were conducted in Xishuangbanna Tropical Botanical Garden in Yunnan province of China. Sticky traps with cotton balls contained 0.5ml solvent or fig volatile compounds were set near fig trees of F. hispida and (F. auriculata) in male phase. Every day at 12:00 and 18:00, the numbers of fig wasps in each trap were recorded. Each observation lasted 2 weeks. Data were analyzed by the Mann-Whitney U test. The results showed that geraniol was significantly attractive to C. solmsi marchali (p<0.05), while vanillin and linalool were attractive in lesser degrees only (p<0.10). Linalool and the extract of receptive figs of F. auriculata were significantly attractive to C. emarginatus, but the number of the wasps trapped by the inter-floral fig extract was even lower than the control. Furthermore, a four-arm olfactometer was used to test the responses of the pollinating fig wasps to 12 fig volatile compounds. The wasps trapped in the arm treated with volatile compound and in the control arm were recorded respectively. Data were analyzed by a paired t-test. The results showed that C. gravelyi were significantly attracted by geraniol and terpineol (p<0.05). The responses of C.solmsi marchali and C.gravelyi to 12 info-chemicals were different, but they both preferred geraniol, linalool, farnesol, vanillin and terpineol to other compounds. C.emarginatus showed greater preference for the receptive fig extracts than the inter-floral ones.The results suggest that the fig-fig wasp specificity might result from the specific combination of several major fig volatile compounds and some particular minor volatile compounds. The results also indicate that pollinating fig wasps have preferences for receptive figs.