Illinois Natural History Survey - University of Illinois

Aphids

Aphids suck the juices out of plants – it’s a living!*
Aphis: “little brown birds” of the aphid world
Soybean Aphid: recent introduction to North America
3I Key to the Genus Aphis

Aphids suck the juices out of plants – it’s a living!*

SoybeanAphid_morphs.jpgAphids are tiny insects in the Order Hemiptera that live by feeding on thephloem sap of plants. Nearly all annual and perennial plants, including shrubs and trees are potential hosts for aphids, which can be found from the growing tips and flowers to the roots.  Aphid feeding often distorts the plant tissues, crumpling leaves, stunting and bending stems, or forming galls.  Aphids excrete honeydew, which is used as a sugar source by many other insects includingants, which are often found tending colonies of aphids.  There are approximately 5,000 described species of aphids (Remaudiere and Remaudiere, 1997), most of which are found in the temperate zones (Blackman and Eastop, 2000). The aphid life cycle is one of the most fascinating among insects because most of the individuals seen are female, clones of their mothers, born pregnant, and give birth to live young.  Some may alternate seasonally between perennial and annual host plants.  Sexual reproduction also plays a part in the lives of most species but male aphids are still unknown for some species of aphids. While most aphid species are not considered plant pests, approximately 10% can be both direct pests of many of the world cultivated crops and excellent vectors of plant viruses.

Many aphids, particularly those that are pests, have a worldwide distribution and most likely accompanied their host plants when invading new areas. Typically those species that are widely distributed have broad host ranges that often include many agriculturally important crops. For example, Aphis gossypii lives on cotton and cucurbits (squashes); the spirea aphid, Aphis spiraecola, is a pest of Citrus even though it was named after an ornamental shrub; the corn leaf aphid, Rhopalosiphum maidis, is the most common aphid on corn, but can also be found on many other grasses, including wheat; and the experimental workhorse of the aphid world,Myzus persicaethe green peach aphid, is found on countless hosts over a broad range of plant families (Blackman and Eastop, 2000).

Aphis: “little brown birds” of the aphid world

Aphis is one of the largest genera in family Aphididae, with an estimated 400 described species (Remaudiere and Remaudiere, 1997) and approximately 150 species in North America (Smith and Parron, 1978).  They can be described as the “little brown birds” of the aphid world, by their often drab coloration and the difficulty with which many members of this ubiquitous group are to distinguish from one another.  Members of the genus Aphis live on a wide diversity of host plants.  Unlike many other aphid genera, which are often limited to members of a single host genus or family, there appears to be no clear pattern of host association among the Aphis.  Most of the species live on non-woody plants and shrubs, but some are found on trees.  Most of the known species of the genus are found in the northern hemisphere but recent molecular work (von Dohlen and Teulon, 2003) suggests that Aphis may be derived from ancestors in the southern hemisphere. 

DorisLagos.jpg

Soybean Aphid: recent introduction to North America

The soybean aphid, Aphis glycines has spread rapidly since its introduction into North America. The first record was in Wisconsin in 2000, and as of 2007 it has been found in all the Midwestern states. In order to control this pest of one of the most important crops in the USA, researchers are studying its ecology, biology, natural enemies, and the appropriate insecticides to use for its control.  A regional suction trap networkhelps track the numbers and spread of this pest, but critical to this endeavor is the ability to identify members of the genus Aphis to the species level.

3I Key to the Genus Aphis

3iAphidMorphol.gifTaxonomists long have recognized the difficulty of writing a traditionaldichotomous key that successfully discriminates among species of the genusAphis because of the high variation within and overlap of the character states of selected morphological features such as antennal segment length, numbers of sensoria on antennal segments, patterns of pigmentation and sclerotization, and numbers and placement of hairs on various body parts. The advent of computerized interactive keys allows users to choose features they can see or are comfortable using to discriminate and discern a best fit among species analyzed by a particular key. Dichotomous keys, which traditionally appeared in printed publications, are less flexible than their newer cousins, because they mandate a single point of entry into the key and make it more difficult to integrate new species into an existing key.  Newer computerized keys can easily integrate relevant images that accurately show different important morphological features, host relationships, and distributions that could be useful in refining and confirming an identification.  In order to fill this need, Doris Lagos (University of Illinois graduate student with David Voegtlin) created a key of Aphis species found in the regional suction trap survey (10 traps) in the Midwest, compiling morphological, host plant, and distributional data to 46 species.  The key uses the 3I software developed by Dmitry Dmitriev.

* modified from a B.C. cartoon by the late Johnny Hart



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