Charlene, a beekeeper in Georgia, described the nightmare she discovered in her only hive. After a summer trip to Nashville, she returned to find foul-smelling honey reminiscent of acetone pooling on the varroa drawer. From there it had sluiced off the edges in viscous globs that rolled in the dirt and settled atop the soil like cocoa-dusted bonbons. Inside the hive, honey frames, slimy and smelly, glinted white with larvae slithering into piles that mounded and flattened like waves on a beach.
Although Charlene purchased used equipment, she had cleaned and scorched every piece to prevent foulbrood. Still, the boxes and frames contained cracks and crevices common in older equipment. In addition, her county was a hotbed of small hive beetles (SHB) and her hive occupied a shady sanctum beneath two leafy peach trees. She thought the site was heavenly, and so did the beetles.
Bands of beetles nudging north
For a while, the small hive beetle (Aethina tumida), an accidental import from sub-Saharan Africa, stayed in the southern states. But as warming trends spread, so did the fortunes of this honey bee pest. A 2019 paper in the journal Global Change Biology1 warned, “Future scenarios of global warming project a vehement increase in climatic suitability for SHB and corresponding potential for invasion, especially in the temperate regions of the Northern hemisphere.” Not pleasant news for beekeepers.
A combination of soil temperature and soil moisture regulates the spread of hive beetles. That’s because, after 13 days of munching on your honeycombs, the larvae leave the hive in great gallivanting groups to pupate in the soil. During this “wandering phase,” the larvae spill over the hive entrance like lemmings and drop onto the soil to search for the perfect spot to mature into adults.
Although the larvae can travel remarkable distances, suitable soil close to the hive is safest because extensive travel for soft, worm-like creatures is always risky. Toasty yet moist soil, not too compact, is the perfect place to dig.
Soil moisture is critical to pupation because it prevents desiccation of the soft-bodied life forms.2 And because warmer soil can shorten the pupation period from about 33 days to roughly 15, beetle populations in steamy soil can expand quickly. As climate fluctuations bring both warmer and wetter summers to many areas, small hive beetles are moving to fresh territory. So what can you do to protect your hives?
Hive beetles exploit the weak and ambush the strong
Beekeepers often compare hive beetles to wax moths because they appear to take advantage of weak colonies with compromised defenses. But others say the beetles can overwhelm even a populous, vivacious colony unless the beekeeper controls their populations. If you plan to establish an apiary in beetle territory, it pays to evaluate your soil type and hive placement.
Other than maintaining strong colonies, beekeepers recommend a suite of control measures, including chemical, mechanical, and biological protocols. In addition, sunlight passed through red acrylic has provided intriguing results in limited tests. Like many other colony threats, including varroa, a program of integrated pest management featuring multiple control measures is most likely to succeed in the long run.
I sometimes hear beekeepers express their indifference to minor infestations: “I don’t worry about small hive beetles because I don’t have many and my bees keep them corralled and helpless.” That sounds nice, but as tame and contained as those beetles may appear, life is bubbling within their shiny brownish-black bodies. Eggs form, spermatocytes divide, and future generations bide their time in the protected warmth of the hive. Ignore them at your own risk.
The landscape of sun and shade
We know that bright sunlight repels adult beetles, so they choose shaded hives instead. Their preference for shade may relate to reproduction because a beetle’s offspring has a better chance of survival in moist soil, something more common in shady areas.
However, beekeepers report that all-day sun is unnecessary for reasonable beetle control. A few hours of shade is okay as long as the hives receive enough direct sun to keep the surrounding soil dry. As a beekeeper, you must heed the health of your colonies even as you fight the beetles, so never keep your colonies so hot that honeycombs melt and bees flee the heat.
As with other pests and predators, try to find their weak spots and attack them when they are most vulnerable.
Pupation: the weak link in the beetle life cycle
So far, the wandering phase of beetle life has been the primary window for control measures. Because the beetles travel away from the colony for pupation, they are vulnerable to beekeeper intervention.
Beekeepers have treated the soil below their hives with pesticides, spread beetle-eating nematodes, and even paved the ground with concrete or covered it with crushed rock to discourage the beetles. Let’s look at some methods for turning their pupation grounds into the enemy.
Soil turned assassin
We can make the soil beneath a hive hostile in several ways. For example, some beekeepers incorporate salt or diatomaceous earth into the ground. Salt will kill the larval and pupal stages of beetles by desiccation, rapidly drawing moisture from their bodies. Salt will also kill most plants, so if you have something you’re trying to nurture, salt may not be your best choice.
Diatomaceous earth sprinkled under a hive will also kill most small creatures that live there. Made of the fossilized skeletons of little sea creatures called diatoms, the tiny fossils are razor sharp and cut into the larvae as they wiggle through the soil, resulting in death by a thousand cuts. Diatomaceous earth is inexpensive, readily available, and works well, but don’t sprinkle it around anything valuable, such as ground-nesting bees.
Roundworms to the rescue
Entomopathogenic (causing disease to insects) nematodes are another popular below-the-hive treatment for small hive beetles. These tiny roundworms infect wandering beetles in their larval or pupal stages by simply crawling through a natural opening, such as the mouth, anus, or respiratory spiracles.
Two main genera of nematodes are popular for combating small hive beetles, Heterorhabditis and Steinernema. These two groups have different methods of “hunting” for small hive beetles, so sometimes one works better than another, depending on soil conditions. The two most commonly used species of Heterorhabditis crawl through the soil and search for their prey, while the two common species of Steinernema stay in one place, lying in wait to ambush their target.3
In all cases, once the nematodes enter the beetle’s body, they release a symbiotic bacterium from their body cavities into the body cavities of the hive beetles. Although harmless to the nematodes, these bacteria wreak havoc on the small hive beetles, releasing a toxin that kills them in 24 to 48 hours. Each species of nematode harbors a unique species of bacteria, so the rate and mode of killing varies with each symbiotic pair.
The best soil for nematodes is sand or moist, loose loam in full or partial shade. Simply mix the worms with water and apply them to the soil with a watering can or sprayer. It’s best to wait until after sundown so the soft-bodied creatures can dig below the surface before they dehydrate. Applying the worms just ….