Abstract
The parasitic mite Varroa destructor is an important contributor to the high losses of western honeybees. Forager bees from Varroa-infested colonies show reduced homing and flight capacity; it is not known whether flight manoeuvrability and related learning capability are also affected. Here, we test how honeybees from Varroa-infested and control colonies fly in an environment that is unfamiliar at the beginning of each experimental day. Using stereoscopic high-speed videography, we analysed 555 landing manoeuvres recorded during 12 days of approximately 5 h in length. From this, we quantified landing success as percentage of successful landings, and assessed how this changed over time. We found that the forager workforce of Varroa-infested colonies did not improve their landing success over time, while for control bees landing success improved with approximately 10% each hour. Analysis of the landing trajectories showed that control bees improved landing success by increasing the ratio between in-flight aerodynamic braking and braking at impact on the landing platform; bees from Varroa-infested colonies did not increase this ratio over time. The Varroa-induced detriment to this landing skill-learning capability might limit forager bees from Varroa-infested colonies to adapt to new or challenging conditions; this might consequently contribute to Varroa-induced mortality of honeybee colonies.
Highlights
The western honeybee (Apis mellifera) is an important pollinator, both in nature and in agriculture
We aimed to answer two main research questions: (i) What is the effect of Varroa infestation of a colony on flight control of the colony’s forager workforce? (ii) What is the functional biomechanical mechanism that causes the potential reduction in flight control of Varroa-infested colonies? For this, we used stereoscopic videography analyses to study how forager bees from Varroa-infested colonies and control colonies land in challenging conditions, i.e. on a vertical platform in an unfamiliar environment
For generalized linear mixed-effects model (GLMM) tests in which we found an effect of Varroa infestation on the dependent variable, 6 we performed corresponding post hoc tests on both the Varroa-infested and control groups separately
Summary
The western honeybee (Apis mellifera) is an important pollinator, both in nature and in agriculture. Apiculture and crop pollination are seriously affected by widespread losses of honeybee colonies [1,2]. Causes for these colony losses are diverse and controversial, but exposure to the parasitic mite Varroa destructor has been suggested as one of the major contributing factors [3]. The mites parasitize both adult bees and the brood and function as a vector for several diseases, such as the deformed wing virus [4]. Active foragers without visual signs of the disease but clinically relevant deformed wing virus infections [11] show reduced flight duration and distance [12,13], similar to the effect of V. destructor [10]
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