Late Summer Yellowjackets Bugging You?
by Jack DeAngelis, PhD of
LivingWithBugs.com
Late
summer is the time for yellowjackets and mosquitoes. Populations of these pesky
insects start to peak around August and then decline by October when the weather
turns cool (obviously we're talking about the northern hemisphere). The pattern
for both, and some other insects as well, is that populations are very low in
spring, build through early summer, peak in late summer and decline to almost
zero by winter. We'll deal with mosquitoes in a later article. For now let's
talk about yellowjackets and paper wasps and what to do abut them.
Yellowjacket Colony Life Cycle
For
most species of yellowjackets the only life stage that survives the winter is
the fertilized queen. All other stages die in late fall and nests are not
re-used. Queens start new colonies in the spring. Spring weather has a
significant impact on nest initiation. Cold, wet weather suppresses nest
development while warm, dry weather helps nest establishment. Once nests are
started worker yellowjackets provision and defend them. Nests grow throughout
the summer so by late August they are at maximum size.
Types of Yellowjackets and Nests
There are many species of yellowjackets. Most are predators and make
relatively small nests. These species are not often encountered. A few species,
however, are notorious as scavengers (not predators). These species also tend to
make larger and more threatening nests. These are the yellowjackets that cause
the problems. Yellowjacket nests come in two basic types - above ground, or
aerial, and below ground nests. They are structurally identical the only
difference is that one is in an underground cavity.
Control of Yellowjackets
In
order to reduce the number of bothersome yellowjackets you should reduce the
number of nests of scavenger species in your area. Unfortunately, while the
familiar yellowjacket traps are useful as decoys (see
www.livingwithbugs.com/yellow.html), they are not effective for controlling
nests. There are really only two ways to control nests and one of them is no
longer available.
If you locate a troublesome nest you can effectively control it with a “wasp
& hornet” spray. Don't use gasoline or other flammable liquid. Using gasoline
this way is illegal and dangerous! In the evening treat the nest opening with
the "wasp & hornet" spray. If possible cover the opening with a rock or soil
(ground nests). Use about a half can of spray per treatment. Some ground nests
may require a second treatment.
The
other method is poison baiting. The idea here is to trick workers into taking a
bit of poisoned bait back to the colony to feed to nestmates and the queen. The
advantage with this method is that you don't need to know where the nest is in
order to control it. Unfortunately the only insecticide that was registered for
this use in the US is no longer available. Work is underway to find a new
toxicant for poison baiting. Perhaps by next year this method will again be
available.
Control of Paper Wasps
Most of the time paper wasps can be left alone - they make small,
non-threatening nests. Paper wasps (Polistes) are distinguished from
yellowjackets (Vespula) by the following body features: paper wasps generally
have a thinner “waist” between the thorax and abdomen and longer hind legs. The
biggest difference, however, is the way they construct their nests.
Yellowjackets make a closed nest with a single opening. The nest is completely
covered by a papery envelope. Paper wasps make an exposed nest, without a paper
envelope, where you can clearly see the individual cells.
Paper
wasps generally make small nests in out-of-the-way places. Also, since paper
wasps are predators they won't be a nuisance at picnics - unless you are serving
live insects! The European paper wasp (Polistes dominulus), however, is a little
different. This wasp is not native to the US and in recent years populations
have exploded from coast to coast. This wasp also builds large nests often in
areas where people may contact them. By sheer numbers and nest placement this
wasp has become a real pest in the US. Unfortunately we don't yet have good
solutions to bring the numbers down. Paper wasps are not attracted to wasp traps
used for yellowjackets.
The hope for European paper wasps is that soon a natural enemy (predator or
parasite) or a pathogen will “find” this non-native species and begin to bring
populations under natural control. Until this happens control nests as you
encounter them with “wasp & hornet” sprays. For more information, including
photos of nest structure, see
www.LivingWithBugs.com/epw.html.
For additional information and related articles visit
www.livingwithbugs.com.
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