Staying in touch: how highly specialised moth pollinators track host plant phenology in unpredictable climates

Background For specialised pollinators, the synchrony of plant and pollinator life history is critical to the persistence of pollinator populations. This is even more critical in nursery pollination, where pollinators are obligately dependant on female host plant flowers for oviposition sites. Epicephala moths (Gracillariidae) form highly specialised nursery pollination mutualisms with Phyllanthaceae plants. Several hundred Phyllanthaceae are estimated to be exclusively pollinated by highly specific Epicephala moths, making these mutualisms an outstanding example of plant–insect coevolution. However, there have been no studies of how Epicephala moths synchronise their activity with host plant flowering or persist through periods when flowers are absent. Such knowledge is critical to understanding the ecology and evolutionary stability of these mutualisms. We surveyed multiple populations of both Breynia oblongifolia (Phyllanthaceae) and it’s Epicephala pollinators for over two years to determine their phenology and modelled the environmental factors that underpin their interactions. Results The abundance of flowers and fruits was highly variable and strongly linked to local rainfall and photoperiod. Unlike male flowers and fruits, female flowers were present throughout the entire year, including winter. Fruit abundance was a significant predictor of adult Epicephala activity, suggesting that eggs or early instar larvae diapause within dormant female flowers and emerge as fruits mature. Searches of overwintering female flowers confirmed that many contained pollen and diapausing pollinators. We also observed diapause in Epicephala prior to pupation, finding that 12% (9/78) of larvae emerging from fruits in the autumn entered an extended diapause for 38–48 weeks. The remaining autumn emerging larvae pupated directly without diapause, suggesting a possible bet-hedging strategy. Conclusions Epicephala appear to use diapause at multiple stages in their lifecycle to survive variable host plant phenology. Furthermore, moth abundance was predicted by the same environmental variables as male flowers, suggesting that moths track flowering through temperature. These adaptations may thereby mitigate against unpredictability in the timing of fruiting and flowering because of variable rainfall. It remains to be seen how widespread egg diapause and pre-pupal diapause may be within Epicephala moths, and, furthermore, to what degree these traits may have facilitated the evolution of these highly diverse mutualisms.

Pollination Using Florivores: From Brood Site Mutualism to Active Pollination

This chapter examines brood site mutualisms, where the pollinators are florivores. In brood site mutualisms, the pollinators are sometimes referred to as nursery pollinators. Here pollination success affects not only plant fitness but also pollinator fitness, and the balance between costs and benefits may be highly variable from place to place and across seasons. There are at least thirteen known nursery pollination systems, and this phenomenon can be divided into three categories. Two of these are relatively unspecialized, where beetle or lepidopteran larvae develop in decomposing flower heads, or where thrips feed in flowers as pollen parasites. The third category is termed “active pollination,” also known as “seed-eating pollination syndrome.” The chapter first considers nursery pollination and thrips as pollen parasites before discussing active pollination, where active pollen transfer occurs and a clear mutualism results.