Last week we watched the miserable fate of aphids as lady beetles descended on their colonies and devoured them with gusto. As I wandered through a different patch of aphid-infested flowers, I was delighted to see another aphid- annihilator, the gorgeous green lacewing investigating the realm of suckers. Adult green lacewings are attracted to the fragrant odors emanating from plants infested with aphids. As they feed on plant sap, aphids produce a waste product called honeydew. The honeydew is a sweet concoction of sugars, amino acids, and other compounds. As this sticky goo degrades, telltale odors waft from the plants. Adult female lacewings that cruise the hood in search of food for themselves and their babes sense aphid-related odors. The scent is like the smell of burgers and fries to a fast food junkie and sends a signal to the mother lacewing that "dinner is served."
Lacewing eggs are deposited at the tip of slender stalks.
Upon arriving on a plant, if the proper cues are present, the female lacewing touches her abdomen to the surface of a leaf and draws out a thin strand of protein. At the tip of this protein stalk, she deposits a single egg. Why she goes to this trouble is not entirely clear. Perhaps, by placing the egg on a stalk, hungry predators including other lacewing larvae are less likely to snack on the tasty egg. After hatching, the tiny larvae, also known as an aphid lion, shinnies down the stalk and begins its search for food. If mom was clever and placed the egg in the right spot, a smorgasbord of aphids awaits nearby.
Lacewings pupate in silken spheres attached to the leaf's surface.
The aphid lion is a close relative of the ant lion we met in bug in a previous episode – "The pits" and a cousin of the crafty debris toting lacewing we visited in “A wolf in sheep's clothing." Like its kin the ant lion, aphid lions have powerful, sickle-shaped jaws that grasp their prey. Once attached to the aphid, a pump in the aphid lion's head enables it to suck the life from the hapless victim. Aphid lions are reported to devour 200 aphids per week and several hundred during the course of their development. After shedding its skin twice to grow, the aphid lion spins a white cocoon and attaches the cocoon to the plant. Within this silken orb the transformation from alligator-like larva to pupa to winged adult takes place. After a few weeks in the cocoon, the beautiful adult lacewing emerges. The adult green lacewing has fantastic green or golden eyes and dozens of veins running through its wings, hence the name lacewing. Lacewings eat nectar and pollen and honeydew produced by aphids and other sucking insects. Voracious lacewing larvae eat a variety of prey in addition to aphids including caterpillars, spider mites, lace bugs, beetle larvae, and eggs of many kinds of plant pests. Aphid lions can be purchased commercially and released on plants to help reduce pest populations. Aphid lions have been used to reduce pests with some success in agricultural crops such as cotton and strawberries and to reduce mealybugs on houseplants indoors and lace bugs on azaleas in landscapes and nurseries. As I watched the aphid lion devour an aphid with remarkable zest, I wondered what our world would be like if aphid lions were the size of the German Sheppard next door.
References
The interesting references “The handbook of biological control” by Tom Bellows and T.W. Fisher and “Biological control in specific crops: Woody Ornamentals” by Paula Shrewsbury and Michael Raupp were used to prepare this episode. To learn more about lacewings, please visit the following web sites.
http://www.entomology.wisc.edu/mbcn/kyf103.html
http://www.inhs.uiuc.edu/cee/biocontrol/predators/habitat.html
http://www.nysaes.cornell.edu/ent/biocontrol/predators/chrysoperla.html