Novel heat-treatment sufficiently controls Varrtoa levels in honeybees colonies

Summary

For decades, the honeybee, Apis mellifera, has suffered from severe colony losses due to the ectoparasitic mite Varroa destructor. Routine chemical treatments fail to mediate equilibrium and often comprise substantial trade-offs like side-effects on the host, parasite-resistance and residues in bee products. Research on alternative, minimally invasive yet resilient measures is scarce. Lower mite tolerance to high temperatures compared to its host has the potential to kill adult parasites or interrupt reproduction within bee brood cells, but readily implementable applications have so far been lacking. We investigated a high-tech approach based on controlled interval-heating of wires integrated into individual combs beeswax foundations. Three apiaries, each with an average of six control and treatment colonies were monitored for two years. Seasonal colony growth dynamics were documented (estimates of worker and brood populations plus pollen and honey stores) and complemented by regular tracking of Varroa infestations. Impacts on various brood stages were evaluated by comprehensive digital brood assessment. Moreover, we conducted dedicated transcriptomic and pathogen profiling for pupae and nurse bee samples. Our field study proves that this innovative heat-treatment permits maintaining mite levels below critical thresholds across seasons. Winter reference-curing (oxalic acid) applied to both groups revealed similar infestations of heat-treated and control colonies, the latter previously being subjected to summer-treatments (formic acid). However, increased mortality particularly of early non-target brood stages, corroborated by altered pupal gene expression, appears to trigger excessive brood compensation of heat-treated colonies, overall translating into relatively decreased worker populations during peak growth, and consequently lower honey harvests. Further refining computational sensitivity of the highly promising prototype may adequately enable this system to achieve widespread successful applicability.