Swarming behaviour and pollination by Cretaceous thrips (Insecta: Thysanoptera)

Direct biotic interactions fossilize in low probability and are difficult to be recognized. This is because they normally occur over a brief time span and the conditions required for their fossilization are exceptional. Swarm behaviour in Thysanoptera (thrips) is a phenomenon that is not yet fully understood but is crucial for the survival and success of representatives of this order of insects. Moreover, the role of thrips as pollinators of gymnosperms had not gained significant attention until the Recent decline in insect populations, particularly pollinators, and the consequent impact on the flora that relies on them. Here we describe a thrips assemblage in Cenomanian Kachin amber (Myanmar, ca. 99 Ma), composed of both, females and males of the new species Burmathrips engeli gen. et sp. nov., belonging to the family Stenurothripidae, that has been interpreted as a swarm. These specimens have Cycadopites-type pollen grains attached to their bodies, with additional associated grains, most likely detached, being abundant in the same amber flow, throughout the amber piece. Nowadays, hexapod aggregations are related to different activities like mating and courtship, but identifying this type of behaviour in the fossil record is difficult. This finding demonstrates the antiquity of mating-related swarming behaviour in thrips, which is consistent with that of their extant counterparts. It also provides direct evidence that gregariousness facilitated the prominent role of thrips as gymnosperm pollinators during the Cretaceous.