INSIGHTS INTO MID-MESOZOIC POLLILNATING INSECTS

Modern associations between insect pollinators and their angiosperm hosts are ecologically multifaceted, providing an important force for driving the evolution of both groups. Extant angiosperm species overwhelmingly are pollinated by insects and such interactions likely played an important role in driving their separate elevated diversities. Middle Jurassic to Early Cretaceous pollinators are a distinctive group of insects consisting of seed-plant-visiting insect species of early-diverging lineages in long-established clades originating in the earlier Jurassic. The principal extant pollinators are Thysanoptera (thrips), Hymenoptera (sawflies, wasps, bees), Coleoptera (beetles), Lepidoptera (moths, butterflies) and Diptera (flies). Mid Mesozoic pollinators were Thysanoptera, Mecoptera (scorpionflies), Neuroptera (lacewings), Diptera, Heteroptera (bugs) and perhaps Orthoptera (grasshoppers, katydids). Differences between these temporally disjunct groups also involved major seed-plant hosts pollinated today versus those of the mid Mesozoic. We provide selected examples of specific associations between pollinators and their host plants and address the nature of reward systems such as pollination drops, nectar, pollen and larval food resources. There are four results. First, major taxonomic differences exist between extant and mid-Mesozoic insect pollinators, attributable to Cretaceous extinction of most gymnosperm lineages and their insect pollinators, and replacement by simplified, efficient, angiosperm pollinator systems. Second, earlier correspondences between distinctive gymnosperm structures of ovulate and pollinate organs and mouthpart features of their insect-pollinators resulted in evolutionary trajectories in gymnosperm‒insect pollination systems not found in later angiosperm‒insect associations. Third, there were special structures occurring in the reproductive organs of pollinated plant hosts that required distinctive pollinator physiologies, behaviors and life habits. Last, evolutionary rates in many insect-pollinator and gymnosperm host lineages likely were inconstant. Fossil and modern evidence ‒ and morphologic, molecular and ecological methods ‒ gradually has addressed these fundamental issues, albeit much work needs to be done.