4.3.1. Assessing reproductive success

Mite reproductive success is defined as the ability of a mother mite to produce at least one viable mated female offspring before the developing bee pupa hatches as an adult. Successful mite reproduction requires the maturation of at least two eggs laid by a reproducing mother mite inside the brood cell: a male mite and a sister female mite, which must mate together before emergence of the host bee. The male mite offspring will die when the bee hatches from the cell, but any mated mature daughter mites will enter the colony’s mite population along with their mother to find a new brood cell for reproduction. A mother mite that lays no eggs, lays only one egg, produces no male offspring, or begins egg-laying too late in relation to larval development, will not contribute any progeny to the mite population. The fecundity (number of eggs laid) is an additional parameter that can determine variation in the number of viable females each mother mite contributes to the population. Fecundity does not necessarily contribute to the mite’s ability to reproduce successfully. Instead, it represents only the number of eggs laid without accounting for the age of the offspring or the likelihood of them reaching maturity. Therefore, fecundity may not be independent from the incidence of delayed egg-laying since any mother mite that begins laying eggs late may consequently lay fewer eggs.

Therefore, information on the following parameters are required to assess successful reproduction: the fertility (whether the mother mite laid eggs); the presence or absence of male offspring; the proportion of dead offspring; and the incidence of delayed egg-laying by mother mites (identified by relating the developmental stage of mite offspring to the developmental appearance and thus the determined age of the infested pupa; see the section ‘Obtaining brood and adults of known age’ in the BEEBOOK paper on miscellaneous methods (Human et al., 2013)). These are important since relatively small differences in reproductive factors can have a large effect on the population dynamics at a population level (Martin and Medina, 2004).