Density of predating Asian hornets at hives disturbs the 3D flight
performance of honey bees and decreases predation success
Abstract
Automated 3D-image based tracking systems are new and promising devices
to investigate the foraging behaviour of flying animals with great
accuracy and precision. 3D analyses can provide accurate assessments of
flight performance in regard to speed, curvature, and hovering. However,
there have been few applications of this technology in ecology,
particularly for insects. We used this technology to analyse the
behavioural interactions between the Western honey bee Apis melifera and
its invasive predator the Asian hornet, Vespa velutina nigrithorax. We
investigated whether predation success could be affected by flight
speed, flight curvature, and hovering of the Asian hornet and honey bees
in front of one beehive. We recorded a total of 603,259 flight
trajectories and 5,175 predator-prey flight interactions leading to 126
successful predation events, representing 2.4% predation success.
Flight speeds of hornets in front of hive entrances were much lower than
that of their bee prey; in contrast to hovering capacity, while
curvature range overlapped between the two species. There were large
differences in speed, curvature and hovering between the exit and
entrance flights of honey bees. Interestingly, we found hornet density
affected flight performance of both honey bees and hornets. Higher
hornet density led to a decrease in the speed of honey bees leaving the
hive, and an increase in the speed of honey bees entering the hive,
together with more curved flight trajectories. These effects suggest
some predator avoidance behaviour by the bees. Higher honey bee flight
curvature resulted in lower hornet predation success. Results showed an
increase of predation success when hornet number increased up to 8
individuals, above which predation success decreased, likely due to
competition among predators. Although based on a single colony, this
study reveals interesting outcomes derived from the use of automated 3D
tracking to derive accurate measures of individual behaviour and
behavioural interactions among flying species.