Thesis (M.S.)--Virginia Polytechnic Institute, 1940. / Abstract. Includes bibliographical references (leaf 65). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute, 1939. / Abstract. Includes bibliographical references (leaves 64-65). Also available via the Internet.

The tobacco flea beetle is one of the major insect pests of tobacco in Virginia. The adult injures the plants by eating small irregular holes in the leaves and the larva by feeding on the roots of the plants. The tobacco flea beetle hibernates in the adult stage in leaves and trash around the edge of tobacco fields and also under trash in the tobacco field, especially around the old tobacco stumps of the previous season. More beetles survived the winter in the soil around the base of the tobacco stumps than in the organic material around these stumps. During the spring of 1938 the tobacco flea beetles emerged from hibernation at Chatham, Virginia, over a period of 70 days. The eggs of the tobacco flea beetle are normally deposited in cracks or small depressions in the soil near the base of its food plant. A female of the overwintering brood deposited 154 eggs during her oviposition period of 53 days. The number of eggs deposited by the later broods were much less and the oviposition period shorter. In the early spring at Chatham, Virginia, the average incubation period for eggs was about 10.5 days, whereas in midsummer eggs generally hatched in from 4 to 7 days. The eggs require a certain amount of moisture for incubation. The larva molted its skin three times. The larva is subterranean in habit and feeds on the roots of the tobacco plant and other plants of the family Solanaceae. The stems of young succulent food plants are often injured by larvae in the second and third instars. Larval records indicate that the larval period may vary from a maximum of 44 days in the early spring to a minimum of 15 days in midsummer. The length of the prepupal period ranged from 1 to 6 days. The pupal stage is passed within an oval shaped earthen cell which is formed by the nature larva. It is usually found about an inch below the surface of the soil. The duration of the pupal period ranged from a maximum of 15 days in the spring to a minimum of 3 days in midsummer. In the fall the pupal period ranged from a minimum of 10 days to a maximum of 16 days. Newly emerged tobacco flea beetles, which are lighter in color than the beetles of the older breed, confine their feeding to the lower leaves which are near the ground. After a few days they spread to other parts of the plant. The preoviposition period for the seasonal broods were as follows: Overwintering brood, 14 days; first brood, 7.5 days; second brood, 7 days; third brood, 9 to 11 days. No eggs were deposited by females of the fourth brood. The tobacco flea beetle deposits very few eggs on air-dry soil as compared with egg deposition on moist soil. The average length of life of individuals of the overwintering brood under caged conditions was approximately 57 days and for the first brood about 53 days. Tobacco is the favorite food plant of the tobacco flea beetle, put other plants of the family Solanaceae are attacked also. The overwintering generation and two later generations of the tobacco flea beetle attacked the tobacco in the field in Pittsylvania County during the season of 1938. There were probably two later broods which were not well defined on suckers during the latter part of the summer and early fall. The tobacco flea beetle was found to be attacked in the adult stage by a hymenopterous parasite; family Braconidae, species Microstonus epitricis (Vier.) The following cultural practices are important in preventing the spread of the tobacco flea beetle: Location of the plant bed, destruction of the plant bed after the plants are set, destruction of suckers, and fall and winter plowing. / Master of Science

A study of the host plants of the tobacco flea beetle was made in Pittsylvania County from April 1 to September 23, 1939. The work was divided into field observations, rearing experiments end population studies. From field observations made throughout the season it was found that this insect fed mostly on the solanaceous plants. especially tobacco. In the spring before the tobacco was transplanted and in the late summer after the harvesting of the crop, the flea beetle fed on a wide variety or plants. Rearing experiments were made using 29 plant species representing 11 families most of which were known as hosts of the adult beetle. These were planted in a small plot of land of a common tobacco soi1. Beetles were caged over these for 4 days and records were kept as to the number of adults that developed from the eggs laid. No beetles emerged from any of the non-solanaceous plants, whereas at least a few developed on all the Solanaceae tested. Many more beetles developed on tobacco, potato and jimson weed than on any of the others. For the population studies tobacco flea beetle and solanaoeous weed counts were made in 14 tobacco fields selected for this purpose. Beetle counts were made at weekly intervals from May 26 until the middle of August and were computed to show the average number of beetles per tobacco plant. Weed counts were made in June and September and were computed to show the average number of weeds per 100 square yards. The data indicated that only tobacco in the beds and potato in the field were of importance in building up the early flee beetle infestation of tobacco. / Master of Science