Small Hive Beetle in Ghana's Cashew Farms

Aethina tumida global distribution map.

Small Hive Beetle

Aethina tumida becomes a severe problem for beekeepers in Ghana’s cashew farms

Stephen Adu, Giacomo Ciriello and Isaac Mbroh, Bees for Development

What was not a problem, now is

Aethina tumida is a beetle species endemic to sub-Saharan Africa and classified as invasive in north and central America and Australia. Commonly known as small hive beetles, they scavenge on honey bee colonies. Upon emerging, adult beetles seek out colonies and hide in hive cracks and crevices. Females lay eggs on or close to comb, so that hatching larvae can feed on brood, honey and pollen. Larvae then leave hives to pupate in soil. Within its local range, small hive beetle is considered a minor pest that tends to infest weak colonies and does not usually cause enough damage for beekeepers to bother with any control methods.

Previously the beetle had not been a problem for beekeeper Stephen Adu, or for other beekeepers working in central Ghana, where apiaries are now a regular sight on the many cashew farms which characterise the landscape around Kintampo, Nkoranza and Techiman. In March 2022 beekeepers noticed more severe infestations of small hive beetles, affecting even their strong colonies and quickly leading to absconding, completely spoilt combs and fermenting, contaminated honey. Stephen contacted Kwame Aidoo Director of Bees for Development Ghana for advice.

Aethina tumida, absconding and spoilt comb

Aethina tumida severe infestation.

To understand the extent of the issue and subsequent damage, Stephen and Isaac interviewed 18 beekeepers in eight communities. All had experienced unprecedented severe infestations of small hive beetle and lost colonies to absconding as a result. This amounted to 593 colonies across 147 apiaries. Isaac estimated the collective economic loss to be about US$/€10,500.

Experimenting with traps and treatments

Kwame provided some options to control the beetle populations. He advised Stephen on making traps with takeaway food boxes, baited with soybean paste and honey and recommended filling crevices in hives. Also spraying neem leaf extract in the soil around hives to disrupt the life cycle as the larvae go to pupate. Stephen observed that beetles often congregated on the top of top-bars, and he developed an idea of combining powdered neem leaves with wood ash and spreading the mix on the top-bars. He trialled these different control methods across 12 apiaries and recorded the outcomes.

Stephen shared news of his experiments with other beekeepers, and many then tried a combination of these methods. Stephen carefully monitored and observed apiaries with severe infestations.

Traps were effective at attracting and stopping beetles, inside and outside hives, but were insufficient by themselves to control large infestations. Making traps required buying plastic containers, mineral oil and soybean paste, plus the additional labour of baiting, setting, checking and cleaning them out.

It was difficult to determine if spraying neem extract solution on the soil surrounding hives was effective in disrupting the beetles’ life cycle. Neem-based bio-pesticides can be powerful antifeedants and disrupt insect growth and reproduction. For the concentration necessary in and around an apiary to effectively weaken and collapse large populations of beetles, it is likely to severely affect honey bee populations, other insects in the vicinity and the many other pollinators collecting from cashew trees. The effects may not be immediately apparent, but no beekeeper wants to use pesticides and risk slowly poisoning their bees and environment.

4. Control methods trialled – (top right) trap inside hives, (top left) trap in apiaries, (bottom right) spraying neem extract on soil, (bottom left) wood ash and neem powder mix on top bars.

5. Traps checked after a week.

Similar concerns apply to covering the top-bars with wood-ash and neem powder mix. Stephen and other beekeepers who tried this method noticed substantially reduced beetle congregations inside the hives one week after application. Anecdotally, this was the most effective control method. Stephen noticed that it was just as effective in hives where, having run out of neem powder, he had applied only wood-ash. In future he intends to try using only wood-ash on the top-bars as treatment for infested hives to reduce the risks associated with neem extracts.

By August 2022, the situation had returned to normal – with severe infestations of small hive beetle observed mostly in weaker colonies. This may be due partly to the effectiveness of control methods, but more significantly to seasonal changes. The beekeepers confronted with this new challenge have learned much, but many questions remain unanswered. A critical one is: how has the balance in the relationship between the honey bee and the small hive beetle tipped in favour of the latter here?

Rotten roots of the problem

Stephen trained as a master beekeeper on the Cashew, Bees and Livelihoods Project run by Bees for Development Ghana 2017-2020. One of the goals of this project was to help a cohort of young people to become professional beekeepers and trainers, managing hundreds of colonies and supporting cashew farmers to keep bees on their orchards. Stephen has 250 colonies of his own and a further 120 on behalf of 16 farmers. Most of these colonies are in apiaries of 15-30 hives on cashew farms.

We believe that this style of intensive beekeeping within areas of intensive cashew nut cultivation is causing an imbalance in the host-scavenger relationship. The mechanism tipping the balance in favour of the beetles is probably the abundance of food. Not only do the beetle populations benefit from access to a lot of colonies, but also to big piles of rotting cashew apples, all in one place. Cashew farmers pick the nuts and leave the apples to rot, as there are no processors buying them and they are not highly regarded as fresh fruit.

Studies show that, with fruit as an alternative food source, small hive beetles are able to complete their life cycle even in the absence of bee colonies (Ellis et al. 2002), that beetles will lay eggs and feed on rotting fruit even when bee colonies are present in the vicinity (Buchholz et al. 2008), and that the presence of an abundant food source other than honey bee colonies may serve as a refuge and be a source of further infestations (Neumann & Elzen 2004). Large apiaries with mounds of fruit rotting on the soil nearby are a haven for small hive beetles.

The roots of the problem are in economic history. Cashew nuts are a cash crop grown for export, mostly unprocessed, that has turned large areas of West Africa into monocultures of non-indigenous trees. Tonnes of cashew apples could be processed into jams or juices, but the local food processing sector remains underdeveloped. Every year hundreds of tonnes of more widely consumed fruits including mangos, oranges and tomatoes go to waste in Ghana because processing or exporting them is not economically viable. Over decades, the lions-share of investments as well as development aid has gone into export-orientated farming rather than developing the national food industry.

Strong and locally adapted honey bee populations may do well in cashew, citrus or oil palm plantations and beekeepers may harvest large honey harvests. But for how long will these bees stay healthy in an environment stripped of biodiversity and diverged from the natural ecosystems in which the bees evolved? In cashew farms, mounds of rotting fruit allow small hive beetle populations to skyrocket and overwhelm even strong colonies. In oil palm plantations, hives are burned, and the bees killed by palm wine tappers. Beekeepers with hives on citrus farms see trees covered with black mould and uprooted to be replaced with cocoa seedlings which leaves little for their bees to feed on.

6. Cashew apples discarded after nut harvesting.

Looking ahead

An important learning point, for those beekeepers who are in it for the longterm, is to seek out and protect apiary sites that offer more diverse and less polluted food sources. Plantations are there and remain an abundant source of nectar that can be exploited for gain, so beekeepers need to continue encouraging farmers to manage their land in pollinator-friendly ways. We must also acknowledge that it will become increasingly difficult to carry on practising natural beekeeping in these unnatural environments. To conserve our strong honey bee populations, we must also be conserving the landscapes in which they developed – diverse forest-savannah parklands.

Stephen is not currently using any of the control methods experimented earlier this year. He is making sure his swarm catching boxes have no cracks and small entrances and that there are plenty around his apiaries so that if a colony absconds due to an infestation, they have somewhere clean to move into and start again. As the next cashew picking season comes along, Bees for Development Ghana will be looking to test our hypothesis that mounds of rotting cashew fruits offer additional breeding grounds for small hive beetle.

Images © Bees for Development Ghana

References

NEUMANN, P.; ELZEN, P. (2004) The biology of the small hive beetle (Aethina tumida, Coleoptera: Nitidulidae): Gaps in our knowledge of an invasive species. Apidologie 35: 229-247 BUCHHOLZ, S.; SCHAFER, M.O.; SPIEWOK S.; PET- TIS J.S.; DUNCAN M.; RITTER W.; Robert SPOON- ER-HART R.; & NEUMANN P. (2008) Alternative food sources of Aethina tumida (Coleoptera: Nitidulidae), Journal of Apicultural Research, 47:3, 202-209 ELLIS J.D.; NEUMANN P.; HEPBURN R.; ELZEN P.J.; Longevity and reproductive success of Aethina tumida (Coleoptera: Nitidulidae) fed different natural diets. Journal of Economic Entomology 2002 95 (5):902-907.