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Dave Black

Experiments with fungi

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This is interesting, in a sort of 'Law of unexpected consequences' kinda way. See here, https://www.nzbees.net/forums/topic/7757-entomopathogenic-fungi/?tab=comments#comment-119565 and here, https://www.nzbees.net/forums/topic/11756-fungi-and-non-chemical-treatment-of-varroa-and-other-illnesses/?tab=comments#comment-185124

 

Summary
Honeybee colonies are under the threat of many stressors, biotic and abiotic factors that strongly affect their survival. Recently, great attention has been directed at chemical pesticides, including their effects at sub-lethal doses on bee behaviour and colony success; whereas the potential side effects of natural biocides largely used in agriculture, such as entomopathogenic fungi, have received only marginal attention. Here, we report the impact of the fungus Beauveria bassiana on honeybee nestmate recognition ability, a crucial feature at the basis of colony integrity. We performed both behavioural assays by recording bee guards’ response towards foragers (nestmate or non-nestmate) either exposed to B. bassiana or unexposed presented at the hive entrance, and GC-MS analyses of the cuticular hydrocarbons (CHCs) of fungus-exposed versus unexposed bees. Our results demonstrated that exposed bees have altered cuticular hydrocarbons and are more easily accepted into foreign colonies than controls. Since CHCs are the main recognition cues in social insects, changes in their composition appear to affect nestmate recognition ability at the colony level. The acceptance of chemically unrecognizable fungus-exposed foragers could therefore favour forager drift and disease spread across colonies.

 

Federico Cappa, Iacopo Petrocelli, Francesca Romana Dani, Leonardo Dapporto, Michele Giovannini, Jeferson Silva-Castellari, Stefano Turillazzi & Rita Cervo. (Feb.2019) Natural biocide disrupts nestmate
recognition in honeybees, Nature Scientific Reports, 9:3171,  https://doi.org/10.1038/s41598-019-38963-3

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Thank you for sharing this with the forum Dave.

My knowledge and some limited experience with entomopathogenic fungi in beehives, includes beauvaria bassiana, lecancillium lecanni and metarhizium. The major problem was keeping the fungi active and alive inside the hive as the thermal death temperature for the fungi was normally just below the temperature of the hive.

Back about 2008 (thereabouts) Plant & Food found this out when they tried to develop metarhizium for varroa control and they could not get it to survive in the hive. The fungi killed varroa and was safe to bees (when tested outside the hive - it showed promise) but the fungi could not be kept alive and therefore active once introduced to the hive. https://www.sciencelearn.org.nz/resources/2453-fighting-a-little-bee-mite 

I am aware of attempts to introduce the other entomopathogenic fungi and they have failed when introduced to the hive.

Temperature and the humidity in the hive appear to be the limiting factor.

 

To be successful in controlling varroa with an entomopathogenic fungi you need to accomplish two things;

1) keep the fungi alive in the hive for a few days at least so it can grow and multiply.

2) in order to grow and multiply the fungal spores needs to attach to the varroa, infect it and then grow and release more spores.

Some photos of beauvaria bassiana infecting cicada here. 

http://www.terrain.net.nz/friends-of-te-henui-group/fungi-te-henui/parasitic-fungi.html

My thinking is that it will be effective on adult varroa only and unlikely to infect larvae.

 

These fungi are used in horticultural covered crops in NZ and the secret to their success is maintaining humidity to enable the entomopathogenic fungi to grow through the crop. Glasshouses can closely control humidity and temperature to ensure success. Growers spray the fungi spores throughout the whole crop so the spores come into contact with the target insects - they stick to the insect, then pentrate the cuticle and then grow, the insect dies and they then release more spores.           

It has occurred to me that in North America that their hives may have a lower interior temperature during winter than ours do in NZ and Australia - but not sure about this.

 

The paper you shared gave me two new insights.

a) the ability to now GC-MS analyse the cuticular hydrocarbons (CHCs) of fungus-exposed versus unexposed bees.

b) that even naturally occurring fungus can affect bees behaviour, especially leading to drift.

 

Thank you for sharing this paper.

 

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