Linking small-scale flight manoeuvers and density profiles to the vertical movement of insects in the nocturnal stable boundary layer

Huge numbers of insects migrate over considerable distances in the stably-stratified night-time 15 atmosphere with great consequences for ecological processes, biodiversity, ecosystem services 16 and pest management. We used a combination of meteorological radar and lidar instrumentation 17 at a site in Oklahoma, USA, to take a new look at the general assistance migrants receive from 18 both vertical and horizontal airstreams during their long-distance flights. Movement in the 19 nocturnal boundary layer (NBL) presents very different challenges for migrants compared to 20 those prevailing in the daytime convective boundary layer, but we found that Lagrangian 21 stochastic modelling is effective at predicting flight manoeuvers in both cases. A key feature for 22 insect transport in the NBL is the frequent formation of a thin layer of fast-moving air – the low-23 level jet. Modelling suggests that insects can react rapidly to counteract vertical air movements 24 and this mechanism explains how migrants are retained in the jet for long periods (e.g. overnight, 25 and perhaps for several hours early in the morning). This results in movements over much longer 26 distances than are likely in convective conditions, and is particularly significant for the 27 reintroduction of pests to northern regions where they are seasonally absent due to low winter 28 temperatures.