Bastiaan M. Drees
Professor and Extension Entomologist,
The Texas A&M University System

 

More than 250 species of aphids, often called “plant lice,” feed on agricultural and horticultural crops throughout the world, and several can be a problem in Texas landscapes. Many ornamental plants in Texas landscapes are suitable hosts for aphids, including bedding plants (especially chrysanthemums), ash, barberry, boxelder, crape myrtle, jasmine, flowering almond, gardenia, hibiscus, hydrangea, mountain ash, oaks, oleander, peach, pear, pecans, pines, roses, vegetables, and viburnum. Aphid infestations can build to severe levels very rapidly because these insects reproduce very quickly. Infestations can be widespread or localized to just a few plants, and they may be worse in some years than in others.

 

Identification

Aphids are small insects, ranging from 1/16 to 1/8 inch (1.5 to 3.5 mm) in length. Aphids are soft-bodied and vary in shape and color. Their bodies may be pear-shaped, globular, oval, spindle-shaped, or elongate, and they may look black, grey, red, orange, yellow, green, brown, blue-green, white-marked, or wax-covered. Even a single species may include several colors and shapes. Aphids may or may not have wings. Winged forms tend to develop in response to changes in the environment, such as decreasing daylight or temperature, deterioration of the host plant, or overcrowding.

The body of the aphid is segmented, and the head is distinct from the thorax and abdomen. The head bears a pair of segmented antennae and mouthparts for sucking plant juices. Toward the rear of the abdomen, a pair of tube-like structures, called “cornicles,” can be found on most species. These structures secrete a defensive fluid. The back end of the body bears the tail and anal plates. The shape and size of these features and the presence of hairs (also called “setae”) help to identify different aphid species.

 

Life Cycle

The life cycle of aphids is rather unusual and can be complex. Most aphids reproduce sexually and develop through simple metamorphosis (overwintering eggs, then nymphs, and then winged or wingless adults), but they can also reproduce through an asexual process called “parthenogenesis” (the production of offspring without mating). These aphids even bear live young, instead of laying eggs.

Most aphids reach sexual maturity in 4 to 10 days, and the reproductive period is about 3 weeks under good environmental conditions. The average lifespan of an adult is about 1 month. Despite their relatively short lifespans, aphids can be quite prolific. In fact, aphids can reproduce faster than any other insect.

The aphid’s variable and complicated life cycle can make these insects difficult to control, because it allows a shortening of time between generations, overlapping of generations, and increased reproduction–all of which can increase the rate of development of resistance to insecticides.

Occasionally, an aphid species seems to dis-appear from one type of plant only to reap-pear some time later. This may be due to a process called “host plant alternation.” These aphids use one plant as the “primary host” for reproduction. Another plant, perhaps a distantly related one, is used as a “secondary host” for parthenogenetic reproduction. Migrants returning to the primary host are winged males and winged parthenogenic females which produce egg-laying sexual females. Later on, winged parthenogenic females return to the secondary host. Some species have lost their host-alternating behavior and have a complete life cycle on a herbaceous secondary-host plant. Both partheno-genesis and host alternation have enabled aphids to exploit food plants, particularly short-lived herbaceous ones. However, many cosmopolitan species are now able to live all year round parthenogenetically on secondary crop hosts, and some have spread to areas where their original (primary) hosts do not even occur.

 

Damage to Plants

Aphids draw sap from plant tissue (phloem) using mouthparts adapted for piercing and sucking. Some aphids feed on foliage, while others feed on the twigs, limbs, branches, fruits, flowers, or roots of plants. Some species inject toxic salivary secretions into plants as they feed. If left unchecked, aphids can stunt plant growth, deform and discolor leaves and fruit, or cause galls to form on leaves, stems, and roots.

As aphid populations develop, infestation sites become littered with empty “skins” (exoskeletons) that the aphids shed during molting. Some species also produce large amounts of white waxy filaments that cover their bodies and litter infested plant parts.

Many aphid species secrete a sticky sub-stance called “honeydew,” which is similar to sugar water. This energy-rich anal secretion falls on leaves and other objects below the infestation. A fungus called “sooty mold” (Capnodium spp.) colonizes on honeydew-covered surfaces, causing them to be covered with a black coating. As a result, sunlight is unable to reach the leaf surface, which restricts photosynthesis which produces the plant sugars. Honeydew-covered surfaces, including car exteriors, decks, and sidewalks, become sticky and blackened with sooty mold.

Honeydew also attracts ants, flies, and other insects. Some aphid species depend heavily on ants for survival and dispersal. The honeydew-loving ants “tend” the aphids and prey upon natural enemies and unhealthy aphids. Ants also carry aphids to uninfested parts of plants. Some ants (Lasius spp.) even harvest and overwinter the eggs of the corn root aphid (Aphis maidiradicis).

Certain aphids are important vectors (spreaders) of plant diseases, particularly viruses. The cotton aphid is known to transmit more than 50 plant viruses, and the green peach aphid more than 100.

 

Monitoring Population Levels

Aphid populations are best monitored by routine (once or twice a week) visual inspections of plants that are potential hosts. Aphids can occur anywhere on the plants, but they are often found on the underside of the leaves or on the new growth. Yellow sticky cards, available from garden stores and nurseries, are effective tools for monitoring winged aphid populations, particularly in greenhouses.

 

Common Species of Aphids in Texas Landscapes

Many aphid species attack landscape plants in Texas. A few of the more common ones are described below.

Cotton or Melon Aphid, Aphis gossypii Glover

Adult aphids (shown in Figure 1) are winged or wingless, soft-bodied, yellow to dark green, and 1/16 inch or less in size. Winged forms have a black head and thorax and hold their wings in a roof-like position over the back of the body.

    Life cycle. Wingless adults overwinter in protected areas, such as field debris and soil, and feed on weed hosts. In the greenhouse, they can be active year-round. In the spring, winged females fly to suitable host plants and produce live nymphs through parthenogenesis. Nymphs develop through several stages (instars) before becoming mostly wingless adults in 4 to 10 days, depending on the temperature. Winged adults are produced when certain environmental conditions occur. Many overlapping generations can occur each year.

   Habitat and food sources. This species feeds on a wide variety of plants (members of 25 plant families!) including begonia, catalpa, citrus, ground ivy, gardenia, hydrangea, vegetables, violets, and weeds. Feeding causes distorted growth, as well as reduced growth, quality, and yield. Honeydew excretions are colonized by sooty mold, causing plants to become unsightly and stressed. Numerous skins shed by developing aphids are also unsightly. These aphids are also important vectors of some plant viral diseases.

Green Peach Aphid, Myzus persicae (Sulzer)

Also known as tobacco or spinach aphid, adults of this species (shown in Figure 2) are small, usually less than 1/8 inch long. The body varies in color from pink to green, sometimes with three darker stripes down the back, and the head supports long antennae and red eyes. Adult aphids may be winged or wingless. The development of wings is usually triggered by environmental changes.

    Life cycle. In Texas, female green peach aphids produce three to six fully formed young a day for several weeks. There may be 30 generations each year. In cooler areas, these aphids overwinter as black, shiny eggs on the bark of peach, plum, apricot, and cherry trees.

    Habitat and food sources. The green peach aphid has a wide range of host plants, including peaches, vegetables, and ornamental crops (flowering and bedding plants including chrysanthemums).

Crape Myrtle Aphid, Tinocallis kahawaluokalani (Kirkaldy)

Adults (shown in Figures 3 and 4) are 1/16 inch long, light green to yellow, with black spots and body markings. On winged forms, the second abdominal segment has a double-pronged hump. Wings are clear with dark markings, and they are held in a roof-like position over the back of the body. Some adults are wingless. Nymphal stages are yellow and wingless.

    Life cycle. Female aphids produce live young, particularly during the summer months. Nymph and adult stages can be found on host plants throughout the year, but appear to build up in higher numbers during the hot summer months.

    Habitat and food sources. This aphid specifically infests crape myrtle. Much of the sap withdrawn from the plant is directly eliminated as honeydew, which becomes infested with sooty mold, producing a dry-looking black coating on the leaf surface. Heavily discolored leaves drop prematurely. The severity of infestations varies from year to year, because populations are affected by environ-mental conditions and the presence of predaceous insects. Crape myrtles were originally imported from Asia, and this aphid species may have been imported with its host. No parasites are known to attack this aphid in Texas, but many lady beetles and other predators commonly eat them.

Oleander Aphid, Aphis nerii Boyer de Fonscolombe

This is a bright yellow aphid with black legs and cornicles (shown in Figure 5).

    Life cycle. These aphids first appear on new shoots, buds, and foliage in the spring. Large populations develop over the summer.

    Habitat and food sources. Host plants are restricted to oleander, butterfly weed, and milkweed. These aphids do not usually affect plant health, although their high numbers and the accumulation of sooty mold associated with honeydew can be a nuisance and unsightly. In most cases, many oleander aphids become infested with a parasitic wasp, Lysiphlebus testaceipes (Cresson). Infested, or parasitized, aphids swell, turn brown, and die. The wasp cuts a hole in the back of the aphid’s abdomen to emerge.

 

Management Considerations

Most aphid populations are moderated by natural controls that include environmental stresses (such as high winds, heavy rains, and extreme temperatures) and natural enemies (such as lady beetles, green lacewings, syrphid fly larvae, damsel bugs, braconid and chalcid wasps, and parasitic fungi). In some cases, doing nothing is the best course of action, because populations naturally build up and decline quickly, particularly when high numbers of natural enemies are present. However, any aphid may be considered a potential pest when conditions are favorable for reproduction and disease transmission. The reproduction rate of aphids depends upon food quality, host plant species, moisture, and temperature. Good horticultural and agronomic cultural methods can help discourage aphid outbreaks.

A list of biological control agents, nonchemical methods, and insecticides for suppressing aphid infestations on ornamental plants is presented in Table 1. When control is necessary, using biological, non-chemical, and least-toxic methods of aphid suppression is encouraged. Dislodging the aphids by spraying the host plants with water at high pressure may be an ideal way to control them on house plants and in small plantings. Also, some natural enemies can be purchased from commercial insectaries and released to help reduce aphid numbers.

Insect growth regulators, microbial insecticides, and insecticidal soaps can help to control aphids while having the least impact on natural enemies (also known as biological control agents). Insect growth regulator products do not kill fully developed, adult aphids. Instead, they work by preventing the insects’ development and are most effective when applied when populations first appear.

Most insecticides are applied to plants as a foliar spray or as a soil treatment. Some foliar sprays (acephate, dimethoate) and soil treatments (disulfoton, imidacloprid, oxamyl) are “systemic insecticides.” These products are taken up by the plant and make its tissues and fluids toxic to the feeding aphids. Non-systemic, contact insecticides must be applied to all infested plant surfaces for best results, because they must come into direct contact with the insects. Several applications at 7- to 10-day intervals, or as instructed by the product label, may be needed before an acceptable level of control is achieved.

In agriculture and nursery crop production, chemical control of certain aphid species is difficult because the aphids have become resistant to certain insecticides. Using some insecticides can even cause aphid populations to dramatically increase after the application is made, possibly because they destroy the aphid’s natural enemies or because the aphids are resistant. Carefully monitor the results from any insecticides applied and stay informed as to which compounds perform well.

Bastiaan M. Drees, Professor and Extension Entomologist

 

Fig. 1. Plaster beetle next to the head of an insect pin.

The occurrence of many very tiny beetles in newly constructed or renovated homes and other structures could be a sign of mold buildup that has been used as a breeding habitat by species in this group of beetles. The plaster beetle, Cartodere constricta (Gryllenhal) is one of a number of minute brown scavenger beetle species in the family Latridiidae (Coleoptera)(Kingsolver and Andrews 1991). These beetles are cosmopolitan, occurring throughout the world, and are primarily found in structures.

These beetles feed on mold (mycophagous). Frequently, they can be found in newly constructed or recently renovated buildings where plaster was not dried sufficiently and became moldy, attracting the beetles and providing food for the developmental stages.

Fully developed adult beetles leave the breeding area, often in high numbers, and congregate around lights and in window sills where they can become a nuisance. Occasionally, these beetles contaminate stored food, feeding on mold rather than directly on the product. Other areas providing mold or mildew that may be colonized by these beetles include air conditioning vents, siding and other areas where moisture buildup can occur due to condensation, water leaks or plumbing.

Management of these, as well as other indoor pests associated with mold and mildew habitats such as booklice (see Booklice publication, EEE-00043), should begin with a thorough inspection of the premises to identify potential breeding areas. Eliminating conditions conducive to mold and mildew growth, such as fixing leaks or plumbing problems, air conditioning condensation, and properly allowing plaster to dry during construction will reduce suitable habitats for these insects to develop. Contact insecticide sprays to kill adults leaving breeding areas address only the symptoms of the problem posed by these beetles – high moisture creating growing conditions for mold that the beetles use as a food source.

Literature cited

Kingsolver, J. M. and F. G. Andrews.1991. Minute brown scavenger beetles in Insect and Mite Pests in Food (J. R. Gorman, ed.) USDA ARS Agric. Handbook No. 655, pages179-184.

Acknowledgements

The author wishes to thank Ed Riley, Associate Curator of the Texas A&M University insect museum for his identification of this species as providing background information and literature for the preparation of this fact sheet. Specimens submitted for identification, both collected May 17, 2010, were collected by J. Rico in Galveston Co. and Wizzie Brown, Extension Program Specialist in Travis Co., TX. Also appreciated are reviews of the manuscript by W. Brown and  Chris Sansone.

Use of high-pressure water spray to dislodge spider mites, aphids, small caterpillars and other pests from host plants has long been suggested as a “non-chemical” or “organic” method of pest control (Meyer and Stone 1989):

Giving infested plants a good, hard hosing down will dislodge many insect pests, particularly aphids, thrips and various caterpillars. Plants should first be inspected to confirm the target pest (p. 69).

Accomplishing this method of pest suppression, however, is not as easy as it sounds. The water pressure in College Station (pressure of water coming out of the end of a hose) is 90 to 100 pounds per square inch (Water Department, College Station, TX, pers. comm.). Merely using ones’ thumb on the end of the hose to produce a high pressure spray can produce a high pressure spray, but using that method to dislodge arthropods (insects and mites) may or may not work in certain situations. Control of the spray is difficult and too much force can shred or otherwise damage plants.

Several hose-end attachments are commercially available that are promoted to be capable of dislodging arthropods like spider mites from plant foliage such as roses (Fig. 1). However, most hose-end attachments available at retail outlets product sprays are either too low in pressure (i.e., Dramm 30 Inch Rain Wand™ (Dramm, P.O. Box 1960, Manitowoc, WI 54221), too fine (i.e., Dramm Fogg-it Nozzle Model C-610 Fine Volume 1 GPM manufactured by Fogg-it Nozzle Co., P.O. Box 16053, San Francisco, CA 94116), or produce too much pressure and volume (i.e., Twist Nozzle manufactured by Gilmour Manufacturing Co. Somerset, PA 15501) to be useful for dislodging arthropods on herbaceous plants. Most of these attachments do not have the length or 90 degree angle for the nozzle(s) to spray the underside of leaves within a plant’s canopy to reach insect and mite harborage sites.

Close-up

Fig. 1. Water Wand for Spider Mites
(top) and Jet-All Water Wand (bottom).

Two wands that work well to dislodge small insects and mites are as follows:

• • Water Wand for Spider Mites (Fig. 1) manufactured by Cecil Stokes 150 Lowe Drive Mabank, TX 75156-8926 Telephone: 903/451-2027 E-mail (theroseman@gbronline.com) The price is $26.50 and with the T-Handle $31.50. The Wand comes in 50 inch, 42 inch, 36 inch.
    This device attaches to your water hose with Gilmore metal on-off valve and has a 1/8 inch diameter galvanize tape-wrapped tube, with rubber handle. The Spraying Systems Co. D7 brass cone-type nozzle is directed at a 90 angle from the tube.Usage notes: This device allows spraying directly upwards from 1 3/8 inches from the ground (the height of the nozzle). The spray is a course, hard spray from a single cone-type nozzle. The device is easily controlled (Fig. 2).

 

• Jet-All Water Wand (Fig. 1) available from Kimbrew-Walter Roses (Jack Walter, 2001 Van Zandt, Co. Rd. 1219, Grande Saline, TX 75140, 903/829-2415; FAX: 903/829-2415): This device attaches to hose with a Gilmour plastic on-off valve quick coupler (female) adaptor. It has a 1 inch diameter aluminum tube with a molded plastic handle. A Lessco 3/4 inch poly-vinylchloride (PVC) adaptor connects the aluminum tube to a curved piece of PVC pipe, the end of which is fashioned with 3 fan-type plastic nozzles directed 90◦ from the end of the curved PVC pipe. The total length of the Jet-All is 55 inches.Usage notes: Due to the curved PVC pipe at the nozzle end of this device, spraying directly upwards can not be accomplished less that 3.5 inches from the ground. However, holding the device at an angle does allow spraying from close to ground level. The three nozzles put out more spray volume than the Water Wand, but was found to be harder to control and carefully direct the spray (Fig. 2).
• There also is a new wand that is called MITEYFINE that works well. Sprayers can be purchased online at the following website: http://miteyfine.com/home.html.The other two sprayer models may no longer be available for purchase.

Fig. 2. Demonstrating use of Water Wand for Spider Mites on tomato (top and bottom left), and home-made Jet-All Water Wand used to spray roses (bottom right).

In trials conducted to evaluate these “Water Wand” devices (Drees and Leroy 1991, Drees 1991), they were found to effectively reduce small arthropods from plants sprayed. These devices, and perhaps others (see Organic Gardening: 1) May/June issue 1995, p. 15; 2) May/June issue, p. 68; and, 3) June/July 2004 issue, page 13), use nozzle that produce a fine, even spray with enough force to dislodge small soft-bodied arthropods like spider mites and aphids. Home-made version have been constructed using nozzles sold for pesticide application soldered onto copper tubing attached to a hose.

Use of these devices would be compatible with biological control programs to dislodge pests before natural enemies are released. In addition, water spray treatments may be capable of removing the sugary honey dew emitted by sucking insects deposited on leaves and objects before it is colonized by black sooty mold.
Many factors affect the success of using high pressure sprays for arthropod control including water pressure. Control of host-specific arthropod pests in sites where there are no neighboring host plants is optimum. If pests being dislodged are merely “blown” from one host plant to another, the population may not be reduced and can actually be spread. This was observed in one trial where two-spotted spider mites were removed from snap peas in a home garden and later found infesting nearby tomatoes (Drees 1991). When dislodging non-host specific arthropods like spider mites, dislodged mites may land on neighboring plants which are suitable alternate food sources. This did not occur, however, when treating host-specific arthropods like crape myrtle aphids or where care was taken to direct the spray away from other suitable host plants as was the case in a miniature rose trial.

Plant canopy density also affects ability to spray undersides of leaves. They provided maximum suppression on open canopy type plants. For instance, plants such as spinach where leaves grow in a fashion similar to roof shingles can present a serious challenge to spray “coverage”. Similarly, plants with low-hanging leaves and ground vines may be difficult to spray. Finally, multiple sprays, started when pest populations are first detected can provide optimum prevention of high populations using high pressure water sprays.

Acknowledgments

The author is grateful for review of this manuscript by James Reinert and Thomas Leroy.

References:

Drees, B. M. and T. R. LeRoy. 1991. Evaluation of alternative methods for suppression of crape myrtle aphids, p. 21-22. In Upper Coast 1990-1991 Entomological Result Demonstration Handbook, Texas Agricultural Extension Service, Texas A&M University System, 46 p.

Drees, B. M. 1991. Suppression of two-spotted spider mites with high pressure water sprays, p. 23. In Upper Coast 1990-1991 Entomological Result Demonstration Handbook, Texas Agricultural Extension Service, Texas A&M University System, 46 p.

Meyer, A. and P. Stone (Eds.) 1989. The Healthy Garden Handbook. A Fireside Book, Simon & Schuster Inc., New York, 192 p.