Prevalence and Reproduction of Varroa and Tropilaelaps in Three Species of Honey Bees in Chiang Mai, Thailand

Abstract

Apis mellifera was anthropogenically introduced to Southeast Asia with the goal of developing a commercial beekeeping industry based on this non-adapted species. Such regional approaches often neglect the potential problems of indigenous parasites and pathogens for the introduced species. Such has been the case when Asian honey bee brood mites quickly took 'advantage' of the presence of A. mellifera, a honey bee species adapted to temperate environments. Today the Asian honey bee brood parasites Varroa and Tropilaelaps are considered to be the most serious acarine pests for A. mellifera colonies in Thailand and throughout Southeast Asia. The giant honey bee (Apis dorsata) is the adapted host of Tropilaelaps spp. and the eastern honey bee (Apis cerana) is the indigenous host of two Varroa species. Some life history information concerning these brood parasites are available and much are based on studies utilizing A. mellifera hosts. However, none of these previous research efforts studied the host preference of T. mercedesae in its adapted host (A. dorsata), population fluctuation and reproduction of both mite genera in concurrently infested A. mellifera colonies, differential reproduction of Varroa haplotypes, and the impact of T. mercedesae on infested hosts.

An examination of A. dorsata comb architecture showed a range of brood cell widths of 5.1-6.1 mm. This observation confirms that cells for rearing drone and worker brood are of a uniform size, which may explain why T. mercedesae has no host gender preference when infesting A. dorsata. The population dynamics of V. destructor and T. mercedesae was also monitored in concurrently infested A. mellifera colonies from September 2011 to September 2012 in Chiang Mai, Thailand. Of the 18,250 worker brood cells examined, 970 were observed to be parasitized; 76% by T. mercedesae and 24% by V. destructor. The results show a significant difference for the infestation rate between mite species and with date of observation. The concurrent infestation of a single brood host was extremely rare (<0.1%). In addition, these studies demonstrated a higher proportion of reproductive success for T. mercedesae (70%), compared to 50% for V. destructor. Although the overall infestation data for A. mellifera worker brood had T. mercedesae as the dominant mite species, the results for drone brood parasitism was the reverse where V. destructor was the more frequently encountered mite species. The fecundity of V. destructor and T. mercedesae (in vivo) as measured in older worker brood, displayed no statistically significant difference (1.7 ±0.1 and1.5 ± 0.1 progeny per foundress, respectively). However, when both mite species were deliberately introduced into a single host, the fecundity of V. destructor (2.2 ± 0.1) was significantly higher than that for T. mercedesae (1.5 ± 0.1). The proportion of reproductive foundress mites (R) was also similar for both mite species under in vitro conditions. An in vitro exchange of Varroa spp. between A. cerana and A. mellifera showed that the Korea (K1) haplotype of V. destructor successfully reproduced in worker brood of both A. mellifera and A. cerana but at a higher rate in A. mellifera brood (45% vs. 9%). In contrast, the Northern Thai (NThai) haplotype of V. jacobsoni reproduced in worker brood of A. cerana (16.5%) only but not in A. mellifera. Although the proportion of NThai that reproduced was considered low, it was still higher than the reproductive success of K1 in A. cerana brood.

Keywords: Varroa destructor, Varroa jacobsoni, Tropilaelaps mercedesae, Apis dorsata, Apis cerana, Apis mellifera, Prevalence, Seasonal abundance, Mite reproduction, Varroa haplotypes, Honey bee mites