Observations on the removal of brood inoculated with Tropilaelaps mercedesae (Acari: Laelapidae) and the mite's reproductive success in Apis mellifera colonies.

This study assessed the response of Apis mellifera to brood deliberately infested with Tropilaelaps mercedesae. The reproductive success of T. mercedesae in mite-inoculated and naturally infested brood was also compared. The presence of T. mercedesae inside brood cells significantly affected brood removal. Thai A. mellifera removed 52.6 ± 8.2 % of the brood inoculated with T. mercedesae as compared to 17.2 ± 1.8 and 5.7 ± 1.1 % removal rates for the groups of brood with their cell cappings opened and closed without mite inoculation and the control brood (undisturbed, no mite inoculation), respectively. Brood removal peaked during the second and third days post inoculation when test brood was at the prepupal stage. Overall, non-reproduction (NR) of foundress T. mercedesae was high. However, when NR was measured based on the criteria used for Varroa, the naturally infested pupae (NIP) supported the highest NR (92.8 %). Newly sealed larvae inoculated with Tropilaelaps collected from newly sealed larvae (NSL) had 78.2 % NR and those inoculated with Tropilaelaps collected from tan-bodied pupae (TBP) had 76.8 % NR. Since Tropilaelaps is known to have a short development period and nearly all progeny reach adulthood by the time of host emergence, we also used two Tropilaelaps-specific criteria to determine NR. Foundresses that did not produce progeny and those that produced only one progeny were considered NR. Using these two criteria, NR decreased tremendously but showed similar trends with means of 65, 40 and 33 % for NIP, NSL and TBP, respectively. High NR in the NIP group may indicate increased hygienic behavior in Thai A. mellifera colonies. The removal of infested prepupae or tan-bodied pupae will likely decrease the reproductive potential of Tropilaelaps. Our study suggests that brood removal may be one of the resistance mechanisms towards T. mercedesae by naturally adapted Thai A. mellifera.