Can Insects Develop Resistance to Insect Pathogenic Fungi?

This paper presents new, important information on the microevolution of insect resistance to the insect pathogenic fungus Beauveria bassiana which will have far-reaching implications for the development of insect pathogenic fungi as biological control agents. We placed successive generations of a melanic population of the Greater wax moth, Galleria mellonella, under constant selective pressure from the insect pathogenic fungus, Beauveria bassiana. Enhanced fungal resistance was observed and larvae from the 25th generation were studied in detail to uncover mechanisms underpinning resistance, and the possible cost of those survival strategies. There are 3 novel, core findings from the study:1.Antifungal resistance in these insects is pathogen species-specific, and probably arises through trans-generational immune priming. The resistance was less obvious in earlier generations, suggesting subtle cumulative changes that are only fully apparent in the 25th generation. 2.The insect’s fecundity is already pushed close to minimum by its melanic phenotype. Therefore, the additional drain on resources required to boost antifungal defence still more, comes not from further compromising life history traits but via a re-allocation of the insect’s immune defences. Specifically during B. bassiana infection, systemic (fat body and hemocoel) responses, particularly the expression of antimicrobial peptides, are damped down in favour of a tailored repertoire of enhanced responses in the integument (cuticle and epidermis) – the foremost and most important barrier to natural fungal infection. 3.A previously-overlooked range of putative stress-management factors are activated during the specific response of selected insects to B. bassiana. This too occurs primarily in the integument, and contributes to antifungal defense and/or helps ameliorate the damage inflicted by the fungus or the host’s own immune responses during the battle between host and pathogen.No other study to date has examined so many genes in this context. Indeed, we show that the epidermis has a great capacity to express defense and stress-management genes as well as the fat body (which is the main tissue producing antimicrobial peptides and has been the traditional focus of attention). We therefore propose a “be specific / fight locally / de-stress” model to explain resource allocation and defence priorities for insects selected for superior resistance to insect-pathogenic fungi. However, we also show that these insects are less fecund and probably at no evolutionary advantage in the wild, implying that the risk is small of biological control agents failing in the field

Behavioural responses of the small hive beetle to volatile components of fermenting honeybee hive products

The small hive beetle, Aethina tumida Murray (Coleoptera: Nitidulidae), is a significant pest of managed honeybees in the USA and eastern Australia. The beetle damages hives by feeding on hive products and leaving behind fermented wastes. The beetle is consistently associated with the yeast Kodamaea ohmeri (Etchells & Bell) Yamada et al. (Saccharomycetales: Metschnikowiaceae), and this yeast is the presumed agent of the fermentation. Previous work has noted that the small hive beetle is attracted to volatiles from hive products and those of the yeast K.\ua0ohmeri. In this study, we investigated how the volatile compounds from the fermenting hive products change depending upon the source of the hive material and also how these volatiles change through time. We used gas chromatography–mass spectrometry and choice-test behavioural assays to investigate these changes using products sampled from apiaries across the established range of the beetle in eastern Australia. The starting hive products significantly affected the volatile composition of fermenting hive products, and this composition varied throughout time. We found 61.7% dissimilarity between attractive and non-attractive fermenting hive products, and identified individual compounds that characterise each of these groups. Eleven of these individual compounds were then assessed for attractiveness, as well as testing a synthetic blend in the laboratory. In the laboratory bioassay, 82.1\ua0±\ua00.02% of beetles were trapped in blend traps. These results have strong implications for the development of an out-of-hive attractant trap to assist in the management of this invasive pest