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Cotton aphid/Melon aphid

Article author: David Kerns
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Cotton Aphid, Melon Aphid

Pest Location

Row Crop, Vegetable and Fruit

Description

Cotton or melon aphids, Aphis gossypii, are highly variable in size and color, varying from light yellow to dark green or almost black. Although size can vary based on environmental conditions, adult aphids tend to be about 1/16th inch in length, are soft bodied and pear shaped. Aphids have piercing-sucking mouthparts and have two protrusions on their rear tips called cornicles. Aphid adults can be winged (alate) or wingless (apterous). The formation of winged types is usually in response to overcrowding or poor host quality. The immatures or nymphs of the aphid are similar in appearance to the adult but smaller.

Origin and Distribution

Cotton aphid is nearly cosmopolitan, having a world-wide distribution. However, host specificity does vary depending on geographic origin.

Habitat & Hosts

Cotton aphids are extremely polyphagous and can feed on a large range of host plants covering 25 plant families. Among many others, notable hosts include asparagus, beans, begonia, catalpa, citrus, clover, cucurbits, cotton, eggplant, ground ivy, gardenia, hops, hibiscus, hydrangea, okra, peppers, potato, spinach, strawberries, tomatoes and violet. Crops typically most affected by cotton aphids include citrus, cotton and hibiscus.

Cotton aphids will initially be found feeding on the underside of new leaves, the plant terminal and flower buds, but as the population grows will infest the under side of older leaves.

Cotton aphids feed using sucking-piercing mouthparts which they use to pierce leaves and ingest copious amounts of plant sap from the phloem. Feeding robs the plant of energy that would otherwise be utilized for growth or fruit production. Heavy and prolonged infestations can cause leaves to curl downward, older leaves to turn yellow and shed, plant fruit may also shed or suffer reduction in size.

Cotton aphids excrete wastes in the form of a syrup-like substance called honeydew. Honeydew will accumulate on the leaves (and other plant structures) giving them a shiny, sticky appearance. A black sooty mold will often grow on the honeydew covering the leaf which may partially inhibit photosynthesis. More importantly, the honeydew may accumulate on the lint of open cotton bolls rendering the lint undesirable for milling.

Cotton aphid is also an important vectors of over 50 plant viruses including cucumber mosaic virus, watermelon mosaic virus 2, and zucchini yellow mosaic virus. These viruses are non-persistent viruses and may be transmitted from aphid to plant in a little as 15 seconds.

Cotton aphids are often attended by ants, which collect an feed upon their honeydew.

Life Cycle

With exception of northern latitudes, cotton aphids in the United States are all females, reproduce asexually (parthenogenically), giving birth to live young without mating. Aphids have a tremendous reproductive capacity and nymphs are born with developing embryos already present; essentially aphids are born pregnant. One female may produce as many as 80 offspring that mature within 8 to 10 days. Thus, it is possible for cotton aphids to have as many as 50 generations per year. These generations also occur as frequently as every 5 to 7 days under optimum conditions. In northern latitudes cotton aphid is capable of producing sexual forms and laying eggs on catalpa and rose of sharon for overwintering purposes.

Wingless adults overwinter in protected areas on catalpa, hibiscus, and a number of weed hosts. In the greenhouse, they can be active year-round. In spring winged females fly to suitable host plants and can disperse great distances via wind and weather fronts.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Predators such as lady beetles, lacewings and syrphid flies, along with parasitoids and aphid-killing fungi are often the most effective means of managing an cotton aphids. These beneficial organisms can effectively prevent aphids from reaching the damaging levels. Aphid tending ants will often protect aphids from predators. Soil and seed applied insecticides offer protection during early plant growth, but foliarly applied insecticides are often necessary on more mature plants. Standard and organically certified insecticides are available, but cotton aphid is notorious for developing resistance to commonly used insecticides so adequate control is not certain.

Related Publications

Citations

Blackman, R.L. and V. F. Eastop. 2000. Aphids on the worlds crops: an identification and information guide 2nd edition. Chichester, UK: John Wiley & Sons Ltd.

Kerns, D.L., J.A. Yates and B.A Baugh. 2015. Economic threshold for cotton aphid (Hemiptera: Aphididae) on Cotton in the Southwestern United States. J. Econ. Entomol.108: 1795-1803.

Suhas, V., D. Kerns, C. Allen, R. Bowling, M. Brewer and M. Parajulee. 2017. Managing cotton insects in Texas. ENTO-075, 38 pp. http://www.agrilifebookstore.org/Managing-Cotton-Insects-in-Texas-p/ento-075.htm.

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Corn earworm

Article author: Pat Porter
Most recently reviewed by: Ed Bynum (2018)

Common Name(s): Corn earworm, Cotton Bollworm, Tomato Fruitworm

Pest Location

Row Crop

Description

Corn earworm moth. Photo: Ed Bynum, AgriLife Extension

Corn earworm moth

The corn earworm is also the pest known as the cotton bollworm and tomato fruitworm and can be found on many garden and farm crops and non-crop vegetation. Adults have buff-colored wings and rather stout bodies. The wingspan is approximately 1½ inches. They are good fliers and can easily move from field to field and often arrive in large numbers on storm fronts. The moths only feed on nectar and are not pests.

 Corn earworm egg. Photo: Pat Porter, AgriLife Extension

Corn earworm egg

However, each female can lay 500 or more eggs. The eggs are laid singly and, when new, are pearly white. The color changes to a yellow/dull white tint over time before hatching. Small caterpillars look much like the small caterpillars of other species, and it is difficult to identify them without a microscope. Corn earworm caterpillars have many microspines on the back and sides of the body, and these are not found on most other common caterpillar pests. Larvae have a tan head and alternating dark and light stripes running lengthwise down the body, and they have numerous tubercles (dark spots) with long spines. Other pest species have stripes as well, but they do not have the abundance of microspines and tubercles, and a 10x hand lens will allow differentiation. There is no “typical” larval color, and it is common to find larvae that are either light green, dark green to grey green, or pink. Full grown larvae are approximately 1.5 inches long.

Origin and Distribution

The corn earworm is a New World insect (Western Hemisphere) and is present throughout this region. It overwinters only in areas with mild winters, but flies to other areas during the course of the spring, summer and fall.

Habitat & Hosts

Corn earworm has a very wide host range, and in Texas is usually the caterpillar found in ears of corn. Other cultivated hosts include tomato, sorghum, cotton, soybean, sunflower, squash, watermelon, potato, sweet potato, asparagus, artichoke, cowpea, snap pea, green bean, cabbage, cantaloupe, collard, cucumber eggplant, pepper, watermelon and others.

Life Cycle

Adults are quite mobile and can lay eggs on any host that is at a susceptible stage. Eggs are often laid near or on fruiting structures, but they can be laid on leaves and stems as well. Moths prefer to lay eggs directly on the green silks of field corn and sweet corn, and the larvae then consume the silk and move toward the ear tip.

Eggs hatch in 3-5 days and there will be five to six larval instars, each separated by a molt to a larger caterpillar. The larval stage lasts from 13 to 31 days depending on temperature. Insects develop faster under higher temperatures. After the last larval stage, the larvae move to the soil and construct a burrow where they will remain while in the pupal stage, which lasts from 10 – 25 days depending on temperature. Adults then emerge and will live for an average of 10 days, some more and some less. Corn earworm overwinters in south Texas, and often flies north carried on storm fronts. There are several generations per year and the insect can be expected to be present for most of the growing season in the south, but only increases gradually in number in more northern parts of the state. However, the growing season starts later in the north, and corn earworm is usually quite abundant by the time vegetables and other crops are susceptible.

Corn earworm larvae are cannibalistic and, even though there may be several small larvae in an ear of corn, these will eventually be reduced to one, or less commonly two, per ear. As fruit feeders, even one larva can cause significant damage in vegetable crops, but in agricultural crops like field corn, corn earworm is rarely an economic worry

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Home garden control options include:

  • Spinosad (Rate varies by brand name)
  • Permethrin
  • Synthetic pyrethroids
  • Bacillus thuringiensis (Bt. subspecies Kurstaki)

See Understanding Common House and Garden Insecticides ( https://citybugs.tamu.edu/factsheets/ipm/ent-4002/ ) for more information on insecticides.

Related Publications

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