I’ve been collecting wood-boring beetles for more than three decades now, and if I had to make a list of “essential” methods for collecting them I would include “beating,” “blacklighting,” and ”rearing.” Beating is relatively straightforward—take a beating sheet (a square piece of cloth measuring 3–5 ft across and suspended beneath wooden, metal, or plastic cross members), position it beneath a branch of a suspected host plant, and tap the branch with a stick or net handle. Many wood-boring beetles tend to hang out on branches of their host plants, especially recently dead ones, and will fall onto the sheet when the branch is tapped. Be quick—some species (especially jewel beetles in the genus Chrysobothris) can zip away in a flash before you have a chance to grab them (especially in the heat of the day). Others (e.g., some Cerambycidae) may remain motionless and are cryptically colored enough to avoid detection among the pieces of bark and debris that also fall onto the sheet with them. Nevertheless, persistence is the key, and with a little practice one can become quite expert at efficiently collecting wood-boring beetles using this method. Blacklighting is even easier—find the right habitat (preferably on a warm, humid, moonless night), set up a blacklight in front of a white sheet, crack open a brew, and wait for the beetles to come!
Rearing, on the other hand, takes true dedication. One must not only learn potential host plants, but also how to recognize wood with the greatest potential for harboring larvae, retrieve it from the field, cut it up, place it in rearing containers, and monitor the containers for up to several months or even years before hitting pay dirt (maybe!). Despite the considerable amount of effort this can take, the results are well worth it in terms of obtaining a diversity of species (usually in good series), some of which may be difficult to encounter in the field, and identifying unequivocal larval host associations. I have even discovered two new species through rearing (Bellamy 2002, MacRae 2003)! Moreover, checking rearing containers can be a lot of fun—in one afternoon you can collect dozens or even hundreds of specimens from places far and wide, depending on how far you are willing to travel to collect the wood. Because of the effort involved, however, the more you can do to ensure that effort isn’t wasted on uninfested wood and that suitable conditions are provided to encourage continued larval development and adult emergence from infested wood the better. It is with this in mind that I offer these tips for those who might be interested in using rearing as a technique for collecting these beetles.
I should first clarify what I mean by “wood-boring” beetles. In the broadest sense this can include beetles from any number of families in which the larvae are “xylophagous,” i.e., they feed within dead wood. However, I am most interested in jewel beetles (family Buprestidae) and longhorned beetles (family Cerambycidae), and as a result most of the advice that I offer below is tailored to species in these two families. That is not to say that I’ll turn down any checkered beetles (Cleridae), powderpost beetles (Bostrichidae), bark beetles (family Scolytidae), or even flat bark beetles sensu lato (Cucujoidea) that I also happen to encounter in my rearing containers, with the first two groups in particular having appeared in quite good numbers and diversity in my containers over the years. Nevertheless, I can’t claim that my methods have been optimized specifically for collecting species in these other families.
First, you have to find the wood. In my experience, the best time to collect wood for rearing is late winter through early spring. A majority of species across much of North America tend to emerge as adults during mid- to late spring, and collecting wood just before anticipated adult emergence allows the beetles to experience natural thermoperiods and moisture regimes for nearly the duration of their larval and pupal development periods. Evidence of larval infestation is also easier to spot once they’ve had time to develop. That said, there is no “bad” time to collect wood, and almost every time I go into the field I am on the lookout for infested wood regardless of the time of year. The tricky part is knowing where to put your efforts—not all species of trees are equally likely to host wood-boring beetles. In general, oaks (Quercus), hickories (Carya), and hackberries (Celtis) in the eastern U.S. host a good diversity of species, while trees such as maples (Acer), elms (Ulmus), locust (Gleditsia and Robinia), and others host a more limited but still interesting fauna. In the southwestern U.S. mesquite (Prosopis) and acacia (Acacia) are highly favored host plants, while in the mountains oaks are again favored. Everywhere, conifers (Pinus, Abies, Juniperus, Tsuga, etc.) harbor a tremendous diversity of wood-boring beetles. To become good at rearing wood-boring beetles, you have to become a good botanist and learn not only how to identify trees, but dead wood from them based on characters other than their leaves! Study one of the many good references available (e.g., Lingafelter 2007, Nelson et al. 2008) to see what the range of preferred host plants are and then start looking.
I wish it were as simple as finding the desired types of trees and picking up whatever dead wood you can findm but it’s not. You still need to determine whether the wood is actually infested. Any habitat supporting populations of wood-boring beetles is likely to have a lot of dead wood. However, most of the wood you find will not have any beetles in it because it is already “too old.” This is especially true in the desert southwest, where dead wood can persist for very long periods of time due to low moisture availability. Wood-boring beetles begin their lives as eggs laid on the bark of freshly killed or declining wood and spend much of their lives as small larvae that are difficult to detect and leave no obvious outward signs of their presence within or under the bark. By the time external signs of infestation (e.g., exit holes, sloughed bark exposing larval galleries, etc.) become obvious it is often too late—everything has already emerged. Instead, look for branches that are freshly dead that show few or no outward signs of infestation. You can slice into the bark with a knife to look for evidence of larval tunnels—in general those of longhorned beetles will be clean, while those of jewel beetles will be filled with fine sawdust-like frass that the larva packs behind it as it tunnels through the wood. Oftentimes the tunnels and larvae will be just under the bark, but in other cases they may be deeper in the wood. Broken branches hanging from live trees or old, declining trees exhibiting branch dieback seem to be especially attractive to wood-boring beetles, while dead branches laying on the ground underneath a tree are not always productive (unless they have been recently cut).
One way to target specific beetles species is to selectively cut targeted plant species during late winter, allow the cut branches to remain in situ for a full season, and then retrieve them the following winter or early spring. These almost always produce well. Doing this will also give you a chance to learn how to recognize young, infested wood at a time that is perfect for retrieval, which you can then use in searching for wood from other tree species in the area that you may not have had a chance to cut. I have cut and collected branches ranging from small twigs only ¼” diameter to tree trunks 16″ in diameter. Different species prefer different sizes and parts of the plant, but in general I’ve had the best luck with branches measuring 1–3″ diameter.
Once you retrieve the wood, you will need to cut it into lengths that fit into the container of your choice (a small chain saw makes this much easier and quicker). In the field I bundle the wood with twine and use pink flagging tape to record the locality/date identification code using a permanent marker. I then stack the bundles in my vehicle for transport back home. Choice of container is important, because moisture management is the biggest obstacle to rearing from dead wood—too much moisture results in mold, while too little can lead to desiccation. Both conditions can result in mortality of the larvae or unemerged adults. In my rearing setup, I use fiber drums ranging from 10-G to 50-G in size (I accumulated them from the dumpster where I work—mostly fiber drums used as shipping containers for bulk powders). Fiber drums are ideal because they not only breath moisture but are sturdy and may be conveniently stacked. Cardboard boxes also work as long as they are sturdy enough and care is taken to seal over cracks with duct tape. Avoid using plastic containers such as 5-G pickle buckets unless you are willing to cut ventilation holes and hot-glue fine mesh over them. While breathable containers usually mitigate problems with too much moisture, desiccation can still be a problem. To manage this, remove wood from containers sometime later in the summer (after most emergence has subsided), lay it out on a flat surface such as a driveway, and hose it down real good. Once the wood has dried sufficiently it can be placed back in the container; however, make sure the wood is completely dry or this will result in a flush of mold. I generally also wet down wood again in late winter or early spring, since I tend to hold wood batches through two full seasons.
I like to check containers every 7–15 days during spring and summer. Some people cut a hole in the side of the container that leads into a clear jar or vial—the idea being that daylight will attract newly emerged adults and facilitate their collection. I’ve tried this and was disappointed in the results—some of the beetles ended up in the vial, but many also never found their way to the vial and ended up dying in the container, only to be found later when I eventually opened it up. This is especially true for cerambycids, many of which are nocturnal and thus probably not attracted to daylight to begin with. My preference is to open up the container each time so that I can check the condition of the wood and look for evidence of larval activity (freshly ejected frass on the branches and floor of the container). I like to give the container a ‘rap’ on the floor to dislodge adults from the branches on which they are sitting, then dump the container contents onto an elevated surface where I can search over the branches and through the debris carefully so as not to miss any small or dead specimens. I use racks of 4-dram vials with tissue packed inside each and a paper label stuck on top of its polypropylene-lined cap as miniature killing jars. Specimens from a single container are placed in a vial with a few drops of ethyl acetate, and I write the container number and emergence date range on the cap label. Specimens will keep in this manner until they are ready to be mounted weeks or months (or even years) later. If the vial dries out, a few drops of ethyl acetate and a few drops of water followed by sitting overnight is usually enough to relax the specimens fully (the water relaxes the specimens, and the ethyl acetate prevents mold if they need to sit for a while longer).
I store my containers in an unheated garage that is exposed to average outdoor temperatures but probably does not experience the extreme high and low temperatures that are experienced outdoors. In the past I wondered if I needed more heat for wood collected in the desert southwest, but I never came up with a method of exposing the containers to the sun without also having to protect them from the rain. Metal or plastic containers might have eliminated this problem, but then breathability would again become an issue. I would also be concerned about having direct sun shining on the containers and causing excessive heat buildup inside the bucket that could kill the beetles within them. Now, however, considering the success that I’ve had in rearing beetles from wood collected across the desert southwest—from Brownsville, Texas to Jacumba, California, this seems not to be a big issue.
If anybody else has tips for rearing wood-boring beetles that they can offer, I would love to hear from you.
Bellamy, C. L. 2002. The Mastogenius Solier, 1849 of North America (Coleoptera: Buprestidae: Polycestinae: Haplostethini). Zootaxa 110:1–12 [abstract].
Lingafelter, S. W. 2007. Illustrated Key to the Longhorned Woodboring Beetles of the Eastern United States. Special Publication No. 3. The Coleopterists Society, North Potomac, Maryland, 206 pp. [description].
MacRae, T. C. 2003. Agrilus (s. str.) betulanigrae MacRae (Coleoptera: Buprestidae: Agrilini), a new species from North America, with comments on subgeneric placement and a key to the otiosus species-group in North America. Zootaxa 380:1–9 [pdf].
Nelson, G. H., G. C. Walters, Jr., R. D. Haines, & C. L. Bellamy. 2008. A Catalogue and Bibliography of the Buprestoidea of American North of Mexico. Special Publication No. 4. The Coleopterists Society, North Potomac, Maryland, 274 pp. [description].
Copyright © Ted C. MacRae 2014