LIBRARY 
 iTATE i tANl BOARD 
 
 E-533 
 
 March 1941 
 
 COTTON ROOT APHIDS AND THEIR CONTROL 
 
 By C. F. Rainwater, 
 Division of Cotton Insect Investigations 
 
 Cotton root aphids are small sucking insects commonly called root 
 lice or blue bugs. They are similar in appearance to the familiar leaf 
 aphids or plant lice that are so often seen on the leaves of cotton and many 
 other plants. All aphids feed by inserting their slender beaks in the plant 
 tissues and sucking the plant juices, but the cotton root aphids differ from 
 the leaf aphids in that so far as known they feed entirely on the underground 
 parts of the plants. Their soft roundish bodies are about 1/16 inch in 
 length when fully grown. Some of the adults are winged but most of them are 
 wingless. The adults give birth to living young, and reproduction continues 
 throughout the winter in the South, although at a slow rate during cold 
 weather. Root aphids are helpless insects, and, while capable of crawling, 
 they cannot move for any distance through the soil to the roots on which 
 they feed. Consequently a relationship has developed between the root aphids 
 and field ants whereby the ants tunnel through the soil and carry the aphids 
 from plant to plant and place them on the roots. The aphids secrete a 
 sweetish liquid, or honeydew, that is the principal source of the ants' 
 food and thus repay them for their help. The relation between the ants and 
 the root aphids is thus of mutual advantage. The aphids have become depend- 
 ent upon the ants for locating their food and are seldom found without the 
 attending ants. This dependence on the ants is used as a basis for aphid 
 control, since disturbance or destruction of the ants reduces the number of 
 root aphids. 
 
 Kinds of Cotton Root Aphids and Their Distribution 
 
 It was formerly thought that the corn root aphid (Anuraphis maidi - 
 radicis (Forbes)) was the only species of root aphid attacking cotton, 
 but recent studies have shown that two other species not previously known as 
 cotton pests in the United States are responsible for part of the damage. 
 Since all three species are called cotton root aphids, common names based 
 on the predominant colors have been used locally as follows: 
 
(1) The white cotton root aphid for Trifidaphis phaseo li (Pass.). 
 
 (2) The green cotton root aphid for Anuraphis maidi -radicis (Forbes). 
 
 (3) The brown cotton root aphid for R hopalosiphum subterraneum Mason. 
 
 The white cotton root aphid causes the most serious damage to cotton, 
 and infested plants usually die. The color ranges from amber through yel- 
 lowish white to milky white. The very young aphids or nymphs are amber 
 colored, changing to whitish as they reach maturity. The adults are more 
 robust than the adults of the other two species and also less active. This 
 species was not known to attack cotton prior to 1934, but since that time it 
 has been found injuring cotton in southeastern Virginia, eastern and central 
 North Carolina, and South Carolina. Judging from the increasing number of 
 complaints received in recent years, this species is apparently spreading or 
 becoming more important as a cotton pest. Every examination of severely 
 injured cotton with a large number of plants killed by root aphids has shown 
 this species to be present, though usually one or both of the other species 
 were also present. 
 
 The green cotton root aphid has long been called the corn root aphid 
 because it is an important pest of corn. This species has been known as a 
 cotton pest for many years and is the one from which the common name "blue 
 bugs" has arisen. However, its color is more green than blue, ranging from 
 bluish green to dark green. The green cotton root aphid is the most widely 
 distributed of the three species and occurs on corn throughout the United 
 States east of the Rocky Mountains. It has been found attacking cotton, 
 however, only in southeastern Virginia, eastern and central North Carolina, 
 South Carolina, and eastern and central Georgia. 
 
 The brown cotton root aphid ranges in color from a very light, almost 
 reddish brown in the nymphs to a very dark or purplish brown in the adults. 
 This species likewise was not known to attack cotton until recently, but 
 since 1934 it has been found on cotton in eastern North Carolina and in 
 northeastern and north-central South Carolina. 
 
 Food Plants 
 
 The cotton root aphids feed on the underground portions of a wide 
 variety of plants. Since they continue feeding throughout the winter, a 
 succession of food plants throughout the year is necessary. When other food 
 plants are abundant the aphid damage to cotton is increased, and control of 
 the aphids is more difficult. 
 
 The green cotton root aphid feeds on the roots of corn, several common 
 legumes, cockleburs, smartweed, a number of grasses, or in brief on prac- 
 tically every weed ordinarily found in corn or cotton fields in the South. 
 This variety of food plants is probably more responsible than any other 
 factor for this species being more widely distributed than the other two. 
 
 The white cotton root aphid is unable to survive on the roots of as 
 many different plants as the green. The principal plants other than cotton 
 are the legumes. Peas, soybeans, crotalaria, lespedeza, vetch, and clover 
 
3 - 
 
 are its most common food plants. Some of these are available as food 
 throughout the year. This aphid also attacks a number of vegetables. 
 
 The brown cotton root aphid is also a rather general feeder but has 
 not been found on the roots of as many plants as the green cotton root aphid. 
 It has been found on the roots of okra, butterbeans, soybeans, cocklebur, 
 rabbit tobacco (or life everlasting), evening primrose, and goose grass. 
 Other host plants of all three species will probably be found as studies 
 are continued. 
 
 Injury 
 
 Since the cotton root aphids are entirely subterranean in habit they 
 are seldom seen unless a special search is made. They feed on the roots of 
 cotton from the time the seeds sprout until the first squares appear on the 
 plants. They cause the greatest damage early in the season before the 
 seedlings become well established. Their sucking of sap causes the young 
 plants to become yellowish, unhealthy, stunted, and in many cases to die. 
 The damage resembles that caused by cool weather or seedling diseases, with 
 which it is often confused. In many instances the plants are severely stunted 
 in growth but recover, causing great irregularities in the size of the plants. 
 All three species of aphids cause similar injury, although the severity of 
 the damage varies considerably with the different species. The injury caused 
 by the green and brown root aphids is usually more in the nature of stunting 
 or retarding the growth of the plants, although plants are killed where the 
 infestation is heavy. The white root aphids nearly always kill the infested 
 cotton plants. Frequently two or all three species are present on the same 
 plants. Often the stand is greatly reduced and the remaining plants are 
 stunted over a considerable acreage (fig. 1). All the plants in a row may be 
 killed for considerable distances as the ants move the aphids from plant to 
 plant along the row through underground tunnels. Infested fields are usually 
 "spotted" or "ragged" in stand and appearance. Often only a portion of a 
 field is severely damaged, but at times whole fields are ruined and have to 
 be abandoned. The stunted plants that recover are later in fruiting and 
 therefore more subject to boll weevil attack than' normal plants. 
 
 How to Recognize Root Aphid Injury to Cotton 
 
 The presence of unhealthy plants early in the season, with ant hills 
 occurring around their bases, is an almost positive indication that aphids 
 are on the roots (fig. 2). Many farmers erroneously think that the ants are 
 damaging the cotton. But if a plant is removed with the soil around the 
 roots intact, and the soil is then carefully removed from the roots, 
 large numbers of these aphids will frequently be seen clustered around the 
 stem and roots. Often the roots will be so completely covered with aphids 
 that it would be difficult to place the point of a pin on the root without 
 touching an aphid. If the plants are simply pulled from the soil, however, 
 no aphids will likely be found, as this pulling has a tendency to strip them 
 from the roots. If the ground is soft, one may push his hand into the soil 
 and remove the plant with the soil around its roots intact. But if the ground 
 is hard, the best method of removing the plant with the aphids attached is to 
 use a trowel or a small garden spade. 
 
Many different kinds of ants are ordinarily found in a cotton field, 
 but only one kind has teen found of enough importance to te considered in 
 the control of cotton root aphids. This ant is L asius niger variety neo - 
 niger Emery and is closely related to the species commonly called the corn- 
 field ant. It is light brown and relatively small, and the mounds which it 
 makes by excavating soil for its burrows are usually found around the base 
 of some plant. This is in contrast to the majority of ants' mounds seen in 
 a field, which are usually in open spaces some distance from plants. Also, 
 the mounds made by this ant in cotton fields in the spring of the year 
 seldom contain any subsoil, as they excavate only deep enough to attend 
 the aphids, and at this season the roots do not reach into the subsoil. 
 Therefore ant mounds which contain soil different in texture from the top- 
 soil are not likely to indicate the presence of root aphids. 
 
 Control 
 
 Experiments conducted at Florence, S. C, on the control of cotton 
 root aphids since 1935 have included the use of repellents, soil fumigants, 
 seed treatment, and ant poisons. The best results were obtained from the use 
 of an ant poison or bait prepared as follows; 
 
 One-half pound of tartar emetic 
 
 One pound of sugar 
 
 One quart of cane syrup 
 
 One gallon of water 
 
 These materials should be thoroughly mixed and brought to a slow 
 boil while being stirred occasionally. The liquid bait is then mixed with 
 cottonseed hulls. About 6 pounds of cottonseed hulls will absorb this 
 amount of poisoned bait and is sufficient to treat from f acre to 1 acre of 
 cotton. The bait is distributed in the field by placing small handfuls in 
 the center of each third row approximately 10 feet apart in the row. The 
 ants quickly come to this bait and feed ravenously. The majority of the 
 ants in the poisoned area usually disappear within 24 hours, and at the end 
 of 48 hours practically none can be found. 
 
 It has been found that the test time to apply the bait is just as the 
 cotton is teginning to sprout. Usually a rain occurs between the time of 
 planting and the time the cotton tegins to come up. This packs the soil 
 and makes it easier for the ants to come to the bait. Best results have teen 
 obtained by applying the bait shortly after a rain on a warm, sunny day, 
 as the ants are usually more active then. It may sometimes te necessary to 
 make two or three applications of the tait at intervals of a week to 10 days 
 to get the desired control, but experiments to date indicate that practical 
 and economical control can te obtained by its use. The tartar emetic bait, 
 if applied as described above and before a large numter of the plants have 
 been killed, will greatly reduce the amount of injury the root aphids will 
 cause. This bait is relatively inexpensive. The cost of the materials 
 necessary to prepare bait for treating 1 acre of cotton, including the cost 
 of cottonseed hulls, is about 35 cents. It is also easily and rapidly ap- 
 plied, and, though poisonous if taken internally, .it may safely te handled 
 with ordinary precautions. 
 
- 5 - 
 Cultural Practices as Aids in Control of Cotton Root Aphids 
 
 It has been observed for several years that root aphids cause more 
 injury to cotton following certain crops than others. Where cotton follows 
 cotton, tobacco, or any of the small grains (oats, wheat, or rye) the injury 
 from root aphids is usually not so severe as where cotton follows corn, soy- 
 beans, or cowpeas. This is probably due to the smaller number of weed host 
 plants that grow among the former crops and the fact that corn, soybeans, 
 and cowpeas are favorite hosts of the aphids. 
 
 Early in the spring the root aphids feed on the roots of many weeds 
 that come up in the cotton fields, Here they multiply rapidly, and large 
 numbers are moved by the ants to cotton roots as soon as the cotton germi- 
 nates. Frequent cultivation early in the spring kills the weeds on which 
 they live and breaks up the ants' burrows. Frequent cultivation during the 
 early stages in the growth of the cotton, particularly following a rain, 
 keeps the soil loose and pulverized and makes it more difficult for the ants 
 to construct tunnels for moving the aphids from one cotton plant to the next. 
 
 It has also been noted that when cotton is planted early and retarded 
 in growth by cool weather the aphids have a chance to become established on 
 the roots before the cotton begins to grow. If root aphids are present, a 
 few days' delay in planting cotton frequently results in stronger, more 
 healthy plants. 
 
 Seed that has been treated with ethyl mercury chloride (Ceresan) dust 
 is being used by large numbers of farmers. This treatment has resulted in 
 better stands of cotton and in plants freer from seedling diseases and more 
 able to withstand root aphid attack. 
 
 The following cultural practices will aid in controlling cotton root 
 
 aphids : 
 
 (1) Break the land thoroughly and keep it free of weeds for several 
 weeks prior to planting. 
 
 (2) Have the seedbed loosely pulverized at the time of planting. 
 
 (3) If possible, avoid planting cotton on land following corn, soy- 
 beans, or cowpeas. 
 
 (4) Treat seed with an organic mercury (Ceresan) dust. 
 
 (5) Do not plant too early. 
 
 (6) Cultivate frequently in the early stages of growth, and as soon 
 as possible after each rain. 
 
 (7) Make side applications of nitrates at chopping time to stimulate 
 growth. 
 
 The information now available indicates that the use of poisoned bait 
 for the ants and the suggested cultural aids will control root aphids on 
 cotton. Further experiments are under way to determine the relation of 
 different host plants to the abundance of root aphids on cotton. It is hoped 
 that crop rotations will be developed that will fit into approved farm 
 practices and* will further reduce root aphid damage. 
 
Figure 1. — A field of cotton with a perfect stand at the 
 beginning of the season that has been severely injured "by 
 cotton root aphids. Note that some of the plants are very 
 much stunted in growth and many of them have been killed. 
 Near Florence, S. C, June 18, 1939. 
 
Digitized by the Internet Archive 
 in 2013 
 
 http://archive.org/details/cottonrootaphidsOOunit 
 
Figure 2. — ^A portion of a cotton row showing the presence of 
 root aphids on the roots of seedling cotton, as indicated 
 by the stimted growth and by the ant hills around the bases 
 of the plants. The plants in the center are being severely 
 attacked by root aphids, and many if not all of them will 
 die. The ants construct tiainels in the ground and move the 
 aphids from plant to plant. Hear Florence, S. C, May 12, 1939. 
 
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