Bee Culture, July 2010

Original Title: Are You Ready For The Beetle?

Walt Wright

An article was published on Propolis where the bees’ defense against small pest larvae was described. At that time this beek had not endured a major concentration of adult small hive beetles. Just didn’t realize how timely the earlier article was at the time. I should add that the tapering of end bars proposed in that submittal did substantially reduce adult beetle hiding places. Small comfort! The beetles found enough hiding places without that.

small hive beetle
We collected a few live beetles in a jar to make measurements of their outer dimensions. The jar and samples were left in the truck for a few freezing nights and the beetles were dead when we took them inside for measurement. Thinking that wouldn't affect the measurements of size, the photo session against a scale in 64ths of an inch proceeded as planned. What was revealed in the photos was much more interesting than the measurements. The beetle is remarkably well adapted to penetration of the bee colony. Forgive me if the following is common knowledge, but it was news to me. The live beetle in the photo 1, extracted from the internet, is not what is available to the bee intent on evicting the intruder from the hive. Head and legs could easily be grasped by the bee, and the intruder thrown overboard. The beetle's defenses have that covered.

small hive beetle

Starting with the oval shell or shield at the top, there is nothing for the bees to grip with their mandibles. The forward plate over the thorax fits together with the abdomen section like pieces of a picture puzzle. And when the head is retracted at the lower edge, the eyes are mere bumps on the lower edge of the shield. The rear tip of the protective shell is a second plate on the abdomen section. On the internet photo, the area tip is shown separated, but in defense, it makes a tight fit with the forward abdomen section.

The adaptation gets more complex as we get into the details. Some of the following is conjecture based on examination of a couple of dead adult beetles under magnification. I don’t have the wherewithal to observe a beetle under attack by a bee. What follows is a combination of observations of beetles in the hive, and interpretation of the pictures provided.

small hive beetle legs
When pursued, the beetle’s legs are outboard of the protective shell for speed and maneuverability. And they can motor. In the open, the bee in hot pursuit, isn’t closing the gap much, if at all. A bee can run at good speed, but the much smaller beetle is competitive on foot. The beetle, at rest in a pit, has no legs showing outboard of the shield that a bee could grasp with its mandibles. We’re guessing that the spikes or pincers at the ends of the legs are to get a good grip on the wax substrate to make it very difficult to move, once hunkered down.

small hive beetle antenna

The famous “paddle” antenna is not outboard of the shield, either, when hunkered down. The picture at left shows the prominent antenna structures folded back on the underside into space tailored to the antenna size and shape. An ingenious adaptation! The right side antenna is outlined for visibility.

My exposure to the beetle has been limited. Smashed one in transferring a nuc to larger quarters in ’08. Suspected there might be others that were not seen. Saw a few, dispatched by the flat of the hive tool later in the season. But in ’09 had taken a colony to the Nashville club training yard on the Ag. Center grounds. That area is overrun with beetles. It was obvious before harvest in July that the population of beetles was growing fast. Ordered traps and the traps didn’t stop the beetle population growth rate.

Removed four (all) honey supers and put them in the freezer for a few days. Saw very few beetles in handling the supers, but when they were removed from the freezer, about 50 dead beetles had collected below. That brought to my attention that one of the beetle’s hiding places is the divided bottom bars that I use. The bees are a little careless about filling that space from the underside of a frame.

Beetles increased in numbers through late summer in spite of traps in the upper levels. In addition to the traps, we tried filling the areas around the top bar ends with wax on hand. The bees showed us where the beetles were hiding by clustering around those areas with beetles the bees could not reach. Frames already in the second – year colony had not been modified to reduce the spaces around top bar ends, as were the new frames of foundation. No beetles at the added, modified frame ends.

Twice, the beetles were shaken off frames, the bees permitted to fly back to the reduced entry, with the top covered, and the beetles left outside the hive. That relief was temporary. To close up the hive top beetle entry places, the inner cover was removed and a screened spacer added for ventilation between the top super and the cover. These efforts to reduce the beetle pressure on the colony were ineffective. Each week, there seemed to be more beetles than the week before.

By early fall, my worst fears were realized. The bees had given up on rousting beetles. The beetles were wandering around, in and out of empty comb at their leisure, without being pestered by the bees. Still, there was no apparent comb damage by beetle larvae. One last effort to reduce in-hive beetle population before putting them to bed for winter was a more thorough external shake-out. Frames with beetles in empty cells were bumped against hive parts to dislodge the beetles. This was done in the first-frost time frame with comb feeding in progress to backfill the brood nest. (Fall forage non-existent). We will not know until February what the 09' season effects actually were.

My concern for this particular colony was their super gentleness. Perhaps they would not be defensive enough to adequately cope with the beetles. They had been selected for use in the training yard for that gentleness. Beginning beekeepers are already a little gun shy about stings and didn't need to be attacked during a demonstration of procedures.

In my years of working almost exclusively with feral stock no effort was made to cull out the extra-defensive bees. My feeling was that “extra-defensive” might be an asset in the wild with multiple adversaries. I would suit up bee tight and let them take their “best shot”. The unanswered question about this colony is - would the beetle have prevailed if this colony were meaner?

There are other characteristics of the Small Hive Beetle (SHB) that tend to make them a formidable foe for both the bees and their keepers. I have no personal knowledge of these features, but they are passed along in the interest of a heads up in the “for what it's worth” department.

The beetle can thrive and reproduce off the land. Although they seek the pollen of the beehive for their young, that source is not required to sustain the population. We don't know yet how far north they can overwinter, but they are reported to be able to overwinter in a hive – warmed by cluster heating. I doubt that the beetle penetrates the cluster, but that may be the case.

The adult beetle can go for extended (undefined) periods without feeding. They can mark time in their hiding place and wait for the opportunity to lay their eggs. The literature, way back, reported that alarm pheromone triggered egg laying. Presumably, the confusion of the moment provided the opportunity for optimum placement of eggs. That may be true. In the super-gentle hive, where no bee tried to sting me for the whole season, even taking away all their honey supers, there was no apparent comb damage by beetle larvae. Note: one super of honey was returned after a few days in the freezer purging beetles.

Beetles are reported to migrate cross-country in a cloud or swarm much like the African locust (a grasshopper). Assuming they are nocturnal creatures, you wouldn't see this happening. Also assuming they prefer the scent of bee colonies, overnight, you could have a major infestation of an apiary. I think this was the case for my friend Rob Koss on the gulf cost. All of a sudden, he was inundated with beetles in multiple outyards. He lost a major portion of his season's honey production to beetle damage.

The SHB apparently does not reproduce on an annual cycle like some with which we are more familiar. The June bug, Japanese, and others emerge from the ground at some seasonal cue, have their reproductive orgy, and are gone until the same time next year. Perhaps the more tropical origins support multiple reproductive cycles when conditions are favorable. In the Nashville demo yard, beetle populations grew from June through October. Another hive in that yard, with less owner attention, was checked in early August. When the inner cover was lifted, an estimated 100 beetles were in sight on the frames of the top super. Scary!

An interesting situation occurred on another hive in the yard. A top bar hive (TBH) that had been very active earlier in the season, suddenly died out. I went through the clean-up with the owner. No bees and no beetles. Some cells had stored pollen – no damage . My active hive was overrun with beetles at the time. Is it possible that the beetles key on the bees and not hive scent? Rhetorical question for the experts. If I hadn't been there, I wouldn't believe it myself.

The enlarged photos were taken by son-in-law Roy with equipment available where he worked. Both the pictures and the odds and ends above are intended to get beekeepers aware that the beetle has a slight edge on the bee colony. And the beetle is prepared to persevere until that slight edge pays dividends. The word from here is get ready.

In the meantime, this ex-beekeeper will be applying beetle measurements to design of a better beetle trap.