the numbers of this species. A dust of superfine flowers of sulphur or a lime-sulphur spray 1 to 75 parts of water gave as high as 99 percent control. The species may be considered as a potential pest of fruit trees in northern states.

But one other genus in this family is known from Ohio. The genus Tetranychus Dufour, as suggested before, had long been used to include all the red spiders. With the splitting of the genus, Tetranychus was retained for those species in which the single sharply-curved empodial claw was cleft to the middle into five or six subequal divisions. The collar tracheae are V-shaped and of fairly uniform diameter thruout their length.

Here again many species have been erected on the basis of color and host, but Dr. Ewing and others have proved this character to have no specific value. The characters of the male copulative organ are now used as the basis of specific determination by some workers. It appears to be less variable than many bases used in the past, but is often difficult to study because of its retractile nature.

The body is generally sub-pyriform and bears dorsally four rows of from six to nine bristles each. The species all spin a web. The silk glands are situated in the anterior portion of the cephalothorax and open near the base of the mandibles, the palpi aiding in the manipulation of the thread as it is emitted.

Tetranychus telarius Linnaeus

Fauna Suecica, 1761, 1974, p. 431

This species was first described as Acarus telarius by Linnaeus in the above citation. Dufour in erecting the genus Tetranychus redescribed it as T. lintearius. Since then it has been described in 4 genera and in no less than 28 species. Most of these were merely color variations.

It has been recorded from many places in Ohio at all seasons of the year. It is the most common of the red spiders found in greenhouses where it may frequently do severe injury to nearly all species of plants. In the field it attacks practically all of our fruit, forest, and shade trees and shrubs as well as the majority of the truck and field crops and flowers. The host list includes upward of 250 species and is too extensive to include here.

Dr. Ewing has given an excellent treatment of the species in Oregon Experiment Station Bul. 121, 1914. The egg laying capacity of the females varies from 8 to 94. Climatic and food factors

influence the variation. The rate of deposition is also quite variable, ranging from a few to many within a short time depending largely on the temperature. The incubation period varies from 3 to 8 days. A larval and two nymphal stages occupy about 10 days, after which the adult appears. The adults remain active from 3 to 4 weeks. Adults and second instar nymphs pass the winter successfully beneath debris and in loose dry soil. They seldom winter in bark crevices. During the mild days of winter the mites may become active, often feed, and, if the mild weather continues for several days, they may oviposit. Overwintering mites appear early in the spring but rapid development is retarded until drier summer weather. Parthenogenesis has been shown to exist in this as well as in other species of the genus. There are 9 generations at Corvallis, Oregon and 16 or more at Batesburg, South Carolina. The annual loss from the attack of this species on all crops amounts to an enormous figure.

An extended survey of greenhouses in all parts of Ohio has shown this species present in all. Many different methods are employed to check its ravages but the loss in greenhouses alone amounts to millions of dollars. Chrysanthemums, roses, sweet peas, violets, carnations, calla lilies, geraniums, Budlium sp., etc., are the most severely attacked, probably because they are the most often grown. Cucumbers, tomatoes, egg plants, etc., when grown under glass, are also severely injured. In all cases feeding is accomplished by inserting the needle-like stylets into the plant and withdrawing the cell sap and leaving the foliage a sickly green to almost yellow color, often followed by the death of the plant if the attack is not checked. The fine web which covers the plants protects the mites from many applications designed to kill them.

Because of the greater succulence of most plants grown under glass it is seldom practical to apply the same remedial measures in the greenhouse that are used in the field. From the fact that red spider development is most rapid under hot dry conditions it would seem that a high humidity would soon check their ravages. The usual and most effective practice in greenhouses is to thoroly syringe the plants with water under at least 25 pounds pressure. A specially designed nozzle should be used, or application be made so as to allow the surplus water to run off onto the walks. Even a moist air will greatly reduce the injury from red spider by killing the mites. By application of the water the mites are knocked from the plants and usually lost in the wet soil of the plant bed. It should be repeated at two or three day intervals. For a few potted

plants in a residence dipping them in a solution of one pound of soap in four gallons of water every four to seven days will soon rid them of the mites. Where the nature of the plants will not permit frequent syringing a dust of superfine sulphur has been found to greatly lessen their numbers.

For control of red spider in the field several procedures, depending on the plants to be treated, can be followed. A severe outbreak of red spider is most likely to accompany a dry season and by knowing the conditions of the preceding year as to the abundance of the mites one may anticipate an outbreak in advance. On the occasion of several outbreaks of red spider on plum and apple in southern Ohio the general program and materials recommended by E. R. DeOng in California Station Bul. 347 was suggested. Excellent results were reported by the growers concerned. The spray consists of 5 lbs. of flowers of sulphur made into a paste with 12 gal. of hot water in which 3/4 oz. of powdered glue has been dissolved and this diluted to make 100 gal. The first application would normally come during the last week of June or the first in July. It is usually sufficient since the mites are not as yet numerous. If one has delayed until the outbreak is severe it will be necessary to make two and possibly three applications at three week intervals, adding 1 gal. of commercial lime-sulphur to each 100 gal. of the above mixture. Dusting is seldom practiced to advantage under orchard conditions.

For truck crops the above spray less the lime-sulphur concentrate is very effective. Dusting is coming into quite general use for combatting truck crop insects. Flowers of sulphur applied as a dust either alone or incorporated in another dust at the rate of 30 lbs. to the acre is quite effective in controlling mites. One application if properly timed is sufficient to remove the menace, but delay may require the application of the material at bi-weekly intervals. To make any spraying or dusting program effective it must be followed carefully and accurately.

Tetranychus telarius L. is one of several species of mites that is cosmopolitan in distribution, being recorded from all continents and many islands. Its hosts are numerous and varied. Distribution has been effected locally by crawling, drifting with flowing water, and by wind blowing the mites and their silken thread onto an adjoining plant. To account for the world-wide distribution we must trace shipments of nursery stock from country to country thruout the world.

Tetranychus multidigituli Ewing

Jour. Ec. Ent., X, 5, 1917, p. 497

But one record of this species, the type material from the bark of Gleditsia tricanthos at Wooster, Ohio, November, 1912, taken by Mr. J. S. Houser, is known for the State. The mites are about .5 mm long by .2 mm broad. Several setae at the tip of the thumb, the short body setae, and the broad truncate-tipped tarsi separate it from the other species. It is apparently a rare species.

A large number of the Trombidoidea are peculiar in having very large palpi; short legs with swollen tarsi; and a body usually red and thickly covered with numerous short setae. Variations in these characters easily separate the forms into several families.

Family Erythraeidae

The family name Rhyncholophidae was long applied to this group of mites. The chelicerae are styliform; the large cephalothorax is on a plane with the abdomen; the dorsal groove, or crista metopica, is usually present; and the eyes are sessile. The crista may be enlarged in one or several places. Its exact function is not definitely known. The five-jointed palpi are prominent and have a well developed claw and thumb. The seven-jointed legs are usually long and slender and terminate in two claws.

The general habits of the group are quite varied and have been but little studied. They can usually be found in mesophytic conditions, climbing about on plants or over the ground. The eggs are deposited beneath debris or in loose soil. The six-legged, orangecolored larvae are parasitic upon a number of insects such as aphids, flies, moths, butterflies, phalangids, etc. When engorged they drop from their host to the ground and become quiescent. Later in the season the adult appears. Some species winter in the egg stage.

A number of genera are included in this family. Representatives of these occur thruout all continents, altho none are now known to be cosmopolitan. Four genera are known from this country. A student of this group will find many unsolved questions of synonomy. Three genera and eight species are thus far known from Ohio.

The genus Atomus does not possess retractile mouthparts nor are the tarsi armed with plumes nor the legs provided with spines. No sexual differences are apparent. There is but a single pair of eyes. The genus was long known as Rhyncholophus and many of our species were described under this name.

Atomus parvipollicus Ewing

Trans. Acad. Nat. Sc. St. L., XVIII, 5, 1909, p. 61

These mites are bright red in color and the body is covered with finely barbed hairs. Mature specimens measure about 1 mm long. From early May to late September adults occur thruout southern Ohio. They have been found both on the plants and on the ground. Large numbers have been taken from the fresh silk of ears of corn. Eggs of Heliothis obsoleta, the corn ear-worm, were often numerous on these ears but no mites were ever observed feeding upon them.

On May 14, 1923 numerous specimens were taken with their stylets deeply inserted in the leaves of young cabbage plants. The mites were numerous in this particular patch. This would suggest a plant feeding habit and account for their presence on the tender corn silk. The anterior legs are kept constantly palpitating while the mite is crawling about and seem to probe the crevices in its path. The species is probably common thruout the State. Dr. Ewing reports the type material from Arcola, Illinois but other records are wanting.

Atomus longilinea Ewing

Bull. Amer. Mus. Nat. Hist. XXXVII, 1917, p. 155

I know of no records other than that of the type material collected by Dr. Ewing at Xenia, Ohio beneath bark of apple trees. It resembles Fessonia sp. Adults measure 2.5 mm long by 1.75 broad. It is not a common species.

Atomus quadrirubripes Ewing

This species has been taken but twice within the State, both times from Chillicothe, one on May 10 in an alfalfa field heavily infested with aphids, and the other July 24 in a field of cabbage badly infected with "yellows". Aphids were numerous in the latter case also. No feeding was observed, but since aphids are known to serve as hosts for the larvae in some cases it is not unlikely that such a relation could exist here. often recorded, altho it does not seem rare.

Atomus robustus Banks

The species is not

Ann. N. Y. Acad. Sci. VIII, 1895, p. 432

This is a large species measuring about 3 mm in length. It is very common in southern Ohio during September. It has always been captured on the trunks of trees where the bright red mites are quite conspicuous. Movement is quite rapid.