Tuesday, September 18, 2012
What’s Buggin’ Me…The Green Lacewing
Another article from Master Gardener Carol Leffler. Enjoy!
Actually, the title of this article is a little bit misleading, but now that you’re here and reading, I want to tell you about a most amazing insect, the green lacewing (Chrysoperla carnea).
If anyone had told me eight years ago that I would be writing an article about an insect, I would never have believed it. I’ve spent decades avoiding bugs, so you can see that my association with our entomologist Urban Horticulturist, Dr. Shibles, has indeed made an impression on my insect education. There’s just something about even a picture of an insect that hasn’t been all that appealing to me over the years. However, gardening in Florida, along with Master Gardening and, most recently, my husband’s wonderful foray into macro-photography have instilled an interest that is now fascinating on a daily basis.
So…consider the green lacewing. Green lacewings are non-specific to Florida, occurring throughout North America. Master Gardeners learn in initial training classes that the green lacewing is one of the "good bugs." But, what else can we learn about this tiny insect that, as an adult, only measures ¾ inch in length? Adjectives that come to mind include "voracious" and "predacious." A single lacewing larva can devour up to 200 aphids or eggs
per week. In fact, young lacewing nymphs are so hungry that hatchlings will readily cannibalize one another. This behavior makes human "sibling rivalry" tame by comparison.
Green lacewings are one of the most common predatory insects available to commercial and home gardeners for purchase, and available as eggs and larval stage. They are probably second only to the well-known ladybug beetle, which is available for "live adult" release. More than 130 insect suppliers in North America currently produce Chrysoperla. If you do intend to use purchased lacewings, take heed, however—because after the hatchlings complete larval feeding (three instars) and become winged adults, they are known to undertake nighttime dispersal flights of many miles before mating, despite the availability of local food sources. They’re travelers! The family tree is expansive. This is probably a reason why insects are so successful. Genetic diversity is assured through wide geographic dispersal, particularly in the case of lacewings. This is a big advantage for urban horticulturists, because the success of a "good bug" is a boon to our efforts in the landscape and the garden.
Some folks (who just "hate bugs") might ask, "Why would I ever like a bug so much I would want to buy some? "What does the lacewing consume? Why is it a favorite "good bug"? How does it thwart the efforts of its enemies?
Let’s start from the beginning—depending on whether one ascribes to the "chicken or the egg" philosophy. The adult female lacewing has a unique manner of laying her eggs so that they are protected from predators, as well as from the cannibalistic predation of "sibling" nymphs. Eggs are deposited one by one at the end of fine silken stalks. This "safe distance" prevents the predation and parasitism by other insects, and cannibalism by the other newly hatched lacewing nymphs. Insects—such as ants—eat lacewing eggs, thereby defending aphids from predators, while also protecting the ants’ food source (honeydew). Insects traverse plant stems never noticing that the eggs (a tasty meal) are singly attached only ¼" to ½" away—like a "Bug’s Happy Meal"—packaged in uniform portions, ready for pick-up, but located way off the main road!
This egg arrangement also provides one of nature’s most beautiful effects if you look quite closely at them. Egg deposits can be found on plant stalks, leaves and fruit—and even on windows or on the sides of buildings. The female is only intent on making sure food sources are nearby for the nymphs after they hatch. Although it seems a plant might be a wiser location, perhaps some insects make better choices than others, much as humans do.
The adult green lacewing (C. carnea) primarily feeds on pollen, nectar and honeydew. Artificial foods can be provided to support lacewing populations, especially as part of an IPM (Integrated Pest Management) program. Commercial preparations of lacewing foods (Wheast®, BugPro™, and Bug Chow®) simulate honeydew, attracting lacewings and some other beneficial insects. UF/IFAS Photo Recipes for home preparations can also be found online, although no specific IFAS recommendations were found. Lacewings are considered good candidates for IPM programs due to demonstrated tolerance or resistance to some pesticides. Always be responsible in pesticide use in the presence of any beneficial insect. If you plan to "feed" lacewings, only older adults in the area may be attracted because "new" adults will still disperse, as discussed earlier. So, let us get back to "what else is on the menu" for a lacewing nymph—besides one another? Lacewing larval instars are desirable predators because they feed primarily on aphids, mealybugs, insect eggs, and small caterpillars. Also readily consumed are leafhoppers, psyllids, whiteflies, spiders, thrips, and mites. In the absence of the above, they will also attack some non-pest and beneficial insects, including ladybug beetles.
The lacewing larva is described as "elongate, spindle-shaped ("alligator-like") with long sickle-like mandibles." It has a soft body with hair-like projections. The mandibles have two tubes that inject strong venom that paralyzes prey, allowing the larva to then suck out the body contents. This is the stuff of which Saturday afternoon sci-fi movies are made! A very effective nutritional lifestyle, except for the insect on the wrong end of the "venom straws"!
Larvae feed for about three weeks before they pupate. Look for their spherical silken cocoons generally found on the undersides of leaves. Because green lacewing larvae feed primarily on aphids, they are commonly referred to as "aphid lions." But…that is not their only common name.
(A divergence here: Descriptions above are consistent with
Chrysoperla carnea. The exceptional behavioral trait discussed below is exhibited by green lacewings not found within Chrysoperla).
This is the coolest part!
Below is an image that demonstrates another common name for the green lacewing larva. That "sucking, crawling, alligator-shaped predatory arthropod" is also referred to as the "trash bug"!
Green Lacewing "Trash Bug"
© Mike Leffler
Remember the "hair-like projections"? Well, it turns out that the larva uses those hair-like projections as "tie-downs" to attach "trash" to his own body. Plant debris, and dining "leftovers" including insect legs and exoskeletons are all part of the "trash collection". This is very effective as camouflage to hide soft body parts from enemies. He functions as a "trash collector" for his environment. Pretty amazing! The camouflage really works too, because sightings (and photographs) of the insect in this form are pretty rare—he’s just too well hidden by his own idiosyncratic behavior! He doesn’t dump his trash;
he recycles it as body armor.
Lacewings can live many months, and that gives them plenty of time to be of benefit to gardeners. In temperate regions, such as Florida, lacewings experience
diapause (a period of suspended growth or development and diminished physiological activity in response to adverse environmental conditions). This allows them to overwinter as adults, extending their longevity long past that of their northern cousins.
Insects are fascinating partners in the world of horticulture. Sometimes they’re with us, and sometimes they’re against us, or at least it seems. Fact is, they all have a function, even if it isn’t readily apparent to us. So remember, when you see an errant insect crawling across your kitchen counter, he’s not "Eek!!! A Bug!"…He’s sort of like a weed—merely out of place! Put him out, and gently admonish him with the familiar "…And stay out!!!"
Video of an adult lacewing laying eggs:
"Beneficial Insects and Mites," T. Henn, et. al., IFAS Publication #ENY-276. http://edis.ifas.ufl.edu/in078
"Natural Enemies and Biological Control", Hugh A. Smith and John L. Capinera, IFAS Publication #ENY-822 http://edis.ifas.ufl.edu/in120
"Green Lacewing" AgriLIFE Extension, Entomology, Texas A & M University
"Green Lacewings", M.A. Carrillo
1, S.W.Woolfolk2 and W.D. Hutchison1, 1University of Minnesota, 2 Mississippi State University (RECOMMENDED) http://www.vegedge.umn.edu/VEGPEST/beneficials/glw.htm
"The Cryptic Song Species of
Chrysoperla" U. Conn. http://www.eeb.uconn.edu/people/chenry/Cryptic_songs.html#cc4