Abstract
Tropilaelaps mercedesae parasitism can cause Apis mellifera colony mortality in Asia. Here, we report for the first time that tropilaelaps mites feed on both pre- and post-capped stages of honey bees. Feeding on pre-capped brood may extend their survival outside capped brood cells, especially in areas where brood production is year-round. In this study, we examined the types of injury inflicted by tropilaelaps mites on different stages of honey bees, the survival of adult honey bees, and level of honey bee viruses in 4th instar larvae and prepupae. The injuries inflicted on different developing honey bee stages were visualised by staining with trypan blue. Among pre-capped stages, 4th instar larvae sustained the highest number of wounds (4.6 ± 0.5/larva) while 2nd-3rd larval instars had at least two wounds. Consequently, wounds were evident on uninfested capped brood (5th-6th instar larvae = 3.91 ± 0.64 wounds; prepupae = 5.25 ± 0.73 wounds). Tropilaelaps mite infestations resulted in 3.4- and 6-fold increases in the number of wounds in 5th-6th instar larvae and prepupae as compared to uninfested capped brood, respectively. When wound-inflicted prepupae metamorphosed to white-eyed pupae, all wound scars disappeared with the exuviae. This healing of wounds contributed to the reduction of the number of wounds (≤10) observed on the different pupal stages. Transmission of mite-borne virus such as Deformed Wing Virus (DWV) was also enhanced by mites feeding on early larval stages. DWV and Black Queen Cell Virus (BQCV) were detected in all 4th instar larvae and prepupae analysed. However, viral levels were more pronounced in scarred 4th instar larvae and infested prepupae. The remarkably high numbers of wounds and viral load on scarred or infested developing honey bees may have caused significant weight loss and extensive injuries observed on the abdomen, wings, legs, proboscis and antennae of adult honey bees. Together, the survival of infested honey bees was significantly compromised. This study demonstrates the ability of tropilaelaps mites to inflict profound damage on A. mellifera hosts. Effective management approaches need to be developed to mitigate tropilaelaps mite problems.
Highlights
Tropilaelaps spp. are ectoparasites of giant Asian honey bees (Apis breviligula, Apis dorsata and Apis laboriosa), the original hosts of tropilaelaps mites[1,2]
Feeding by tropilaelaps mites support the proliferation of Deformed Wing Virus (DWV) in the colonies[10,12,13,14]
This study demonstrates that T. mercedesae feeds on post-capped brood, and on pre-capped stages of A. mellifera
Summary
Tropilaelaps spp. are ectoparasites of giant Asian honey bees (Apis breviligula, Apis dorsata and Apis laboriosa), the original hosts of tropilaelaps mites[1,2]. Whether the clinical symptoms that are thought to be associated with DWV are mere manifestations of the degree of feeding injuries sustained by host honey bees or the synergistic effects of both wounds and pathogen load warrants further study Other viruses such as Black Queen Cell Virus (BQCV) have been detected in tropilaelaps mite-infested honey bees, but not in tropilaelaps mites[12]. T. clareae (most likely referring to T. mercedesae) are short-lived (~2 days) on adult honey bees[20,21], but lived longer (~four weeks) when fed unlimited supply of 4th instar larvae[22] These mites are normally seen scurrying on combs with varying ages of brood especially in highly infested colonies[23]. By examining pre- and post-capped stages of brood from field colonies, we (1) determined if tropilaelaps mites feed on unsealed brood as a result of their high mobility on combs, (2) described the types of injuries sustained by host honey bees (unsealed larvae to adults), and (3) assessed if the incidence of viruses was associated with the presence of wound scars in pre-capped brood, and in uninfested and mite-infested capped brood
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