Gil Leclercq

Drawbacks and benefits of hygienic behavior in honey bees (Apis mellifera L.): a review

The hygienic behavior of honey bee workers contributes to the social immunity of colonies. The ability of workers to detect and remove unhealthy or dead brood prevents the transmission of brood diseases inside the colony. Over the last five decades, this trait has been extensively studied and improved in several research and breeding programs. Given the strong interest for hygienic behavior, we here review the costs and benefits associated with this trait, extending preceding reviews on this subject from the late 1990s. Since the 1990s, there have been no major new insights on the efficiency of this behavior against American foulbrood and chalkbrood. However, the number of publications on hygienic behavior against the mite Varroa destructor has considerably increased, fueling the debate regarding the efficiency of hygienic behavior against this parasite. Breeding programs have shown that selection for a specific trait might also impact other traits. Thus, we also review the cost of trade-offs between hygienic behavior and other economically important traits for bee breeders. Overall, the benefits of hygienic behavior seem to largely outweigh its costs for both colonies and bee breeders.

Bioassays to Quantify Hygienic Behavior in Honey Bee (Apis Mellifera L.) Colonies: A Review

Individual immunity in honey bees (Apis mellifera L.) is complemented by highly evolved social behaviors. Among them, hygienic behavior has a key role involving the detection and removal of unhealthy or dead brood. Since the 1960s, several bioassays have been developed to quantify the hygienic behavior of honey bee colonies against chalkbrood, American foulbrood, and varroa infested brood. Here, we review the five main bioassays used since the late 1960s. We describe their advantages and disadvantages, including a special focus on their inherent biases. For each assay, we also discuss whether or not their use should be restricted to quantify the hygienic behavior against chalkbrood, or American foulbrood, or varroa infested brood. Overall, the bioassays involving the removal of freeze-killed brood are recommended over the bioassays relying on the removal of pin-killed brood but only for the quantification of hygienic behavior toward chalkbrood and American foulbrood. These bioassays are not recommended to quantify the hygienic behavior toward varroa infested brood, for which an accurate assessment should rely on assays based on the removal of brood artificially infested with varroa mites. Choosing an appropriate bioassay is crucial for an accurate assessment of the hygienic behavior against a defined pathogen, depending on the research question, or the goal of the breeding program. Bioensayos para cuantificar el comportamiento higiénico en las colonias de abejas melíferas (Apis mellifera L.): una revisión La inmunidad individual de las abejas melíferas (Apis mellifera L.) se complementa con comportamientos sociales altamente evolucionados. Entre ellos, el comportamiento higiénico tiene un papel clave en la detección y eliminación de crías enfermas o muertas. Desde la década de 1960, se han desarrollado varios bioensayos para cuantificar el comportamiento higiénico de las colonias de abejas melíferas frente a la cría infestada de Ascosfera, loque americana y varroa. Aquí revisamos los cinco principales bioensayos utilizados desde finales de la década de 1960. Describimos sus ventajas y desventajas, incluyendo un enfoque especial en sus sesgos inherentes. Para cada ensayo, también discutimos si su uso debe ser restringido o no para cuantificar el comportamiento higiénico contra la cría de loque americana o la cría infestada de varroa. En general, los bioensayos que involucran la eliminación de la cría muerta por congelación son más recomendables que los bioensayos que dependen de la eliminación de la cría muerta por pin, pero sólo para la cuantificación del comportamiento higiénico hacia la cría infestada de Ascosfera y la loque americana. Estos bioensayos no se recomiendan para cuantificar el comportamiento higiénico de la cría infestada de varroa, para lo cual una evaluación precisa debe basarse en ensayos basados en la extracción de la cría infestada artificialmente con ácaros de la varroa. La elección de un bioensayo apropiado es crucial para una evaluación precisa del comportamiento higiénico frente a un patógeno definido, dependiendo de la pregunta de investigación o del objetivo del programa de cría.

Hygienic removal of freeze-killed brood does not predict Varroa-resistance traits in unselected stocks

In honey bees (Apis mellifera L.), hygienic behavior of workers against Varroa destructor provides the colonies with some resistance to this parasite. The removal of freeze-killed brood (FKB) has often been used as a proxy to assess the removal of Varroa-infested brood. The question is whether this approximation is reliable enough to estimate the benefits induced by the removal of Varroa-infested brood in unselected stocks. For this purpose, we investigated the relation between the removal of FKB and three other variables: (1) the percentage of pupae and workers infested by V. destructor; (2) the share of mites in brood compared to phoretic mites; and (3) the reproductive success of mites. To be a reliable estimate, the removal of FKB should correlate with these three variables. Since hygienic behavior is naturally expressed and highly variable in unselected stocks, we chose to use such stocks to get a wide range of FKB removal. There was no correlation between FKB and the three other variables. We conclude that removal of FKB is not a good estimate for hygienic behavior towards Varroa mites in unselected stocks.