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Bees & Beekeeping: Present & Past

Summer Heat and Small Hive Beetles

- July 1, 2022 - Wyatt A. Mangum - (excerpt)

With the heat of the summer comes increased trouble from small hive beetles in areas where they have become a problem, particularly in the Southeast. For new beekeepers, they need to know the life history of small hive beetles early on to avoid their destructive consequences. Let’s begin with identification.

Small hive beetle eggs are tiny and rarely observed by beekeepers. Identification comes from larvae and adults. The beetle larvae should not be confused with greater wax moth larvae. Small hive beetle larvae have distinguishing characteristics. Beetle larvae have two rows of little spines running down their back, which are entirely lacking with wax moth larvae. Beetle larvae have three pairs of slender, short, almost pin-like legs, a structure radically different from wax moth legs (see Figure 1). The beetle larvae are whitish in color, although they can appear in shades of light brown if they have been crawling through the slime they produce.

Looking closely in a hive after the colony had suffered an initial invasion by numerous adult beetles (for up to a couple of weeks), I have found thousands of tiny speck-like, newly-hatched beetle larvae. That was the onslaught of beetle larvae, “arising” to slime the contents of the combs. The time for sliming is largely dependent on the temperature: the hotter, especially with warm nights, the faster the larvae grow.

When a small hive beetle larva is almost a centimeter long, its head capsule and spines become somewhat more noticeable. The larvae are mature enough to leave the hive. In contrast to immature larvae shunning the light, mature ones become attracted to it and crawl out of the hive. Beetle larvae have been observed leaving the hive in the evening. I have seen them leave on hot humid nights, after first congregating at the hive entrance, absent bees. For ground not too hard or dry, most of the larvae enter the soil within a couple feet of the hive entrance and dig down several inches. Years ago, I dug the ground in front of a colony consumed by small hive beetles. I wanted to observe firsthand a larval distribution in a local soil (Virginia).

For a dark loose soil (with some sand) formed under the detritus of an oak-tree climax-canopy, the leaf litter raked back to bare soil, a high concentration of larvae occupied the radial distance about two feet from the front (center) of the hive. Farther away, the larvae thinned out. Statistically and biologically, one would expect a small minority of larvae to be in the soil several more feet away, but that amount of digging was too much. As we will see, I reproduced the high concentration of larvae in the ground.

Down in the soil, the larva forms a small well-defined underground chamber (see Figure 2). Here, the larva develops into a pupa (see Figure 3). The adult beetle digs its way out of the soil and back to the surface. Newly emerged beetles are a light red brown in color and gradually darken to black with age (see Figure 4). If seen in the hive, these reddish beetles indicate recent reproduction, presumably in apiary soil.

Generally, the adult small hive beetles are about six millimeters long and three millimeters wide. This size allows passage through the screen of a package-bee shipping crate or through the eight-mesh wire of a screened bottom board used to monitor and reduce varroa populations.

Beetles are difficult for worker bees to evict from the hive. When harassed by a bee, a beetle withdraws its antennae and legs, and effectively hides under its convex armored body (see Figure 5). After becoming sexually mature in about a week, female beetles lay eggs in cracks and crevices in the hive or on brood comb if not prevented by the bees.

In the hive, the adult beetles find restrictive spaces where the bees cannot reach them. The bees also corral small hive beetles in these places. In the bee house, during my queen introduction experiments, queen cages are tight against the glass of the observation hives. Usually a beetle or two finds that intervening gap between the cage and glass, only to be confined there by the bees (see Figure 6).

Finding a colony dead and the hive overrun with small hive beetle larvae is the situation we want to avoid (see Figures 7 and 8), although it also occurs in feral colonies. I once saw a cut-open bee tree full of small hive beetle larvae. Remarkably, the bee tree had come in with a load of logs on a logging truck. On the scale that weighed incoming trucks, the personnel noticed a weak trickle of surviving bees leaking to flight from the load. They eventually found me to call. Away from the massive piles of logs being processed, I found a cut-open hollow full of beetle larvae and slime. As I remember, a few hundred bees were out of reach in the intact part of the dark hollow. When the bee tree was cut, handled by the logging machine, and put in a pile of other processed logs at the cutting site, the combs had to be broken.

Here is an important observation. When combs “touch,” they actually form gaps small enough for beetles to be out of reach from the bees. Now the colony is in jeopardy. In the heat of the summer, the beetles have the advantage, and the colony is doomed from them alone. In the protected places the beetles lay eggs. If the beetles have access to plenty of resources between the combs (pollen, honey, and brood), expect an explosion of beetle larvae.

While dying feral colonies would seem to always turn into massive sources of small hive beetles, that may not always be true, the beetle reproduction not being that efficient (even without the destruction from cutting the bee tree). Consider briefly this case from the summer of 2015, a colony living under a rural house. After a preliminary noninvasive exam earlier in the season, the beekeeper who was first notified and I returned in September to remove the colony, expecting an involved extraction of bees and honey.

Rather we found a colony nearing its final demise with most of its combs devoid of any bees (see Figure 9, left). Figure 9 (right) shows a removed brood comb with honey, pollen, and a small scattering of sealed brood. Strangely absent were beetle larvae and adults. And where were the greater wax moths, so prevalent in the heat of the summer? In upcoming articles, we will return to the “hive under the house.”

To photograph the density of pupating small hive beetles in the soil without releasing them, I used the following method (not recommended for beekeeping use). I filled a five-gallon bucket with loose fine dirt about eight inches deep. I attached the bucket to the front of a top-bar hive with a colony that had perished and the hive contents were being consumed in the fashion of Figure 7. My top-bar hives are on elevated hive stands so the bucket could fit under and around the alighting board. I inspected the hive all around to make sure no other holes could release beetle larvae (all had to use the three lower entrance holes).

When beetle larvae leave the hive, they just fall off the edge of the alighting board, something I have observed in the evening and at night when out checking my hives. So mature beetle larvae, searching for pupation soil, merely fall in the dirt bucket, never reaching the ground. After it seemed a large number of beetle larvae had left the hive, I carefully removed the dirt from the bucket. I tried to preserve horizontal layers to see an approximation of the underground beetle density in front of a hive, understanding the bucket can artificially confine and concentrate them (see Figure 10).

Maintaining strong colonies to cover their combs is one of the general recommendations for controlling small hive beetle reproduction. That of course is not always easy when confronted with  ….