Tetragonula carbonaria and disease : behavioural and antimicrobial defences used by colonies to limit brood pathogens

Abstract

The honey bee, Apis mellifera, is suffering heavily from the impacts from intensive management. Pests and diseases contribute to the population losses experienced globally. Brood disease is of concern for the apiculture industry because of the direct effects it has on population numbers and despite control measures; resistance to antibiotics and pesticides are common. Alternative pollinators such as stingless bees, including Tetragonula carbonaria, appear to be less impacted by brood diseases. However, there is very little information regarding why this is so. Prior to this study, there are only a few indications about a possible bacterial brood disease in Brazilian stingless bees (Kerr 1948, Nogueira-Neto 1997), with no follow up investigations, and no cases of brood disease losses in Australian stingless bees. As a result, this study presents information on the behavioural and antimicrobial defences of T. carbonaria colonies as mechanisms to limit the development of brood pathogens. In addition to these aims and objectives, this study also introduces and documents the first disease causing brood pathogen in Australian stingless bees. Therefore, the interaction of the defence mechanisms and the identified brood pathogen was also explored. Suitable nest conditions need to exist to sustain pathogen growth and development. Apis mellifera pathogens such as Paenibacillus larvae and Ascosphaera apis utilise nest conditions, especially in the brood area for growth. The limited number of stingless bee pathogens may be related to brood temperature. Thermoregulation behaviour has been investigated in a number of stingless bee species; however, Australian studies are limited to Austroplebeia australis (Halcroft et al. 2013b) and greenhouse maintained T. carbonaria colonies (Amano et al. 2000, Amano 2004, A. Tse, pers. comm., 2011), with outcomes applied to their pollination servicing. This study (Chapter 2) investigated T. carbonaria thermoregulation behaviours during fluctuating ambient temperatures and the influence these have on brood production. Over the 13-month study, T. carbonaria was able to maintain brood temperatures between 15""31ºC, despite ambient temperatures ranging from 0""37°C. The recorded brood temperatures resulted in colonies maintaining yearlong brood development, which would suggest that this could provide a suitable resource for pathogen development year-round. However, pathogen occurrences are rare, it is speculated that the greater brood temperature range which is tolerated by colonies, is ultimately unsuitable for brood pathogen development, especially the lower winter temperatures.

Date of Award	2015
Original language	English