Descriptive Analysis of the Varroa Non-Reproduction Trait in Honey Bee Colonies and Association with Other Traits Related to Varroa Resistance

Abstract

In the current context of worldwide honey bee colony losses, among which the varroa mite plays a major role, the hope to improve honey bee health lies in part in the breeding of varroa resistant colonies. To do so, methods used to evaluate varroa resistance need better understanding. Repeatability and correlations between traits such as mite non-reproduction (MNR), varroa sensitive hygiene (VSH), and hygienic behavior are poorly known, due to practical limitations and to their underlying complexity. We investigate (i) the variability, (ii) the repeatability of the MNR score, and (iii) its correlation with other resistance traits. To reduce the inherent variability of MNR scores, we propose to apply an empirical Bayes correction. In the short-term (ten days), MNR had a modest repeatability of 0.4, whereas in the long-term (a month), it had a low repeatability of 0.2, similar to other resistance traits. Within our dataset, there was no correlation between MNR and VSH. Although MNR is amongst the most popular varroa resistance estimates in field studies, its underlying complex mechanism is not fully understood. Its lack of correlation with better described resistance traits and low repeatability suggest that MNR needs to be interpreted cautiously, especially when used for selection.

Evaluation of Traits for the Selection of Apis Mellifera for Resistance against Varroa Destructor

“…In contrast, SMR cannot be reproduced and each reading must be considered as a one-time assessment. This argument for SMR seems supported with high repeatability for short intervals and low repeatability for longer intervals [ 24 ].…”

“…This seems well in line with the findings of this study, even though these colonies were artificially infested with mites, while in the present study we worked with natural infestation levels. We are not aware of published data on the repeatability of REC or SMR thus far, except a recent publication [ 24 ] where the estimated repeatability for SMR was 0.43 ± 0.11 when readings were only 10 days apart, and 0.17 ± 0.09 when they were separated by a longer time and spread over the season. The latter estimate is close to ours, both in terms of timing as in the level of the repeatability.…”

Advances and perspectives in selecting resistance traits against the parasitic mite Varroa destructor in honey bees

“…However, recent studies did not confirm this biased removal towards cells containing reproducing mites [ 73 , 115 ]. Yet other studies did not find any correlation between MNR and VSH values at the colony level [ 116 ]. These results indicate that the association between traits may vary between populations.…”

“…Similarly, rates of mite removal by VSH doubled after colonies were fed with sugar water [ 141 ]. Trade-offs between foraging and VSH behavior as well as an effect of the brood to honey stores ratio in the colony on VSH have also been noted [ 116 ]. MNR was found to be lower in colonies during periods of greater pollen availability [ 142 ].…”

“…Few studies have performed repeated measurements to assess whether and how much the large number of host, parasite or environmental factors affect the expression of resistance traits [ 116 , 157 ]. Performing such repeated measurements during colony evaluation processes has nevertheless been suggested for different traits to ensure data reliability [ 61 , 116 , 157 – 159 ].…”