Extension Communications
Extension 4-H Youth Building
Ames, Iowa 50011-3630
(515) 294-9915
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Extension Communications |
7/26/04
Contacts:
Betsy Matos, Entomology, (515) 294-1999, bmatos@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Garden Column for the week of July 30, 2004
The Insect Clones - Aphids
By Betsy Matos
Entomology Graduate Student
Iowa State University
In recent years, human cloning has been a topic of extensive discussion, but in the insect world cloning is old news. Cloning, or parthenogenesis, is a way of life for several insects including aphids. Parthenogenesis is reproduction where an unfertilized egg develops into an individual and only the mother's traits are passed on.
In temperate regions such as Iowa's, aphids undergo both parthenogenesis (asexual reproduction) and sexual reproduction. During the spring, a female will hatch from over wintered eggs and produce many live offspring. All of the new offspring will be wingless females. These females then produce more offspring and so on. An outbreak of aphids is likely to occur within a few weeks due to their parthenogenetic abilities. Once the host plant has been overwhelmed with aphids, the females produce female aphids with wings. These winged females are able to move and colonize a new area.
Aphids can produce many generations, sometimes more than 10 in one single summer season. In the fall, some of these females will produce males so that they can mate with other females. After mating, the female lays the overwintering eggs.
More than 1,300 species of aphids have been identified. Aphids and their relatives such as leafhoppers, cicadas and treehoppers are known for sucking plant juices and transmitting pathogens that cause disease.
One characteristic that distinguishes aphids from similar insects is a pair of tubes at the end of the abdomen called cornicles. It is believed that aphids use cornicles as a defensive mechanism to secrete a waxy liquid to protect themselves against natural enemies.
Aphids are an important food source for many insects that help keep our gardens healthy. Ladybeetles, spiders, hover flies, minute pirate bugs and lacewings primarily eat aphids. Ants, however, do not feed on aphids. Instead, when ants and aphids are together, they form a unique relationship called symbiosis. A symbiotic relationship occurs when two insects live in close association for a period of time. The ants provide protection to the aphids from other predators and, in turn, the aphids excrete 'honeydew,' which the ants eat. Honeydew is a sugary substance produced by an aphid after it digests plant juices. Ants become a problem when we release natural enemies in our gardens and greenhouses, because they protect their aphid food source.
Aphids are extremely noxious agricultural pests because of their reproductive capability, their relationship with ants and their ability to transmit pathogens. Moreover, the accumulation of honeydew on plant leaves may create an ideal environment where some sooty molds can develop.
In other cases, however, aphids can be natural enemies of invasive plants. For example, purple loosestrife is an introduced plant that has become invasive in many wetlands throughout Iowa and the United States. An accidental introduction of the purple loosestrife aphid, Myzus lythri, has served as an herbivore in the biological control of purple loosestrife in many areas of the U.S. This aphid is specific for purple loosestrife. The purple loosestrife aphid has collected in areas where purple loosestrife is abundant. The purple loosestrife aphid is serving as another potential natural enemy to reduce purple loosestrife's stand in Iowa.
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Editors: A color photo, suitable for publication, is available by contacting Dr. Marlin Rice (merice@iastate.edu) at 103 Insectary, Dept. of Entomology, Iowa State University, Ames, IA 50011-3140, 515-294-1101, FAX 515-294-8027. A thumbnail is shown at right. Caption: An ant tends a colony of soybean aphids. In 2003, the tiny soybean aphid caused tens of millions of dollars in crop losses in the Midwest. (Photo provided by Marlin E. Rice.) |
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