234 THE PEANUT— THE UNPREDICTABLE LEGUME 



Biology. Development of the tobacco thrips is gradual, but approaches 

 a complete change (55). Eggs deposited in tissues of the foliage hatch in 

 about 7 days in South Carolina (156). The immature form passes 

 through two larval stages, during which feeding occurs, the two stages 

 requiring 5 to 6 days. According to Hooker {77), the mature larva 

 "crawls to some obscure nook," becomes inactive and pupates.® This stage 

 is quiescent and does not feed. At the end of 3 to 4 days the adult emerges 

 and shortly begins feeding. The time for development from egg to adult is 

 approximately 16 days, the period being shorter in warm weather and 

 longer when the temperatures are relatively low. 



Breeding of the tobacco thrips is continuous throughout the warmer 

 months. Five overlapping generations have been reported (49) in South 

 Carolina from April 10 to October 18. The female lives for an average of 

 approximately 30 days and deposits 50 to 60 eggs (156). Nonfertile eggs 

 produce males and fertile eggs apparently produce only females (135, 49, 

 157). Males live for a shorter period than females and are usually less 

 numerous in the field. 



The tobacco thrips presumably hibernate under grass or in other 

 protected places. It is possible that intermittent breeding takes place on 

 wild and cultivated host plants during the warmer periods of the winter 

 in the southern range of the insect, but specific evidence on this point is 

 lacking. So far as is known, only the adult females over-winter (49) . 



Volunteer peanuts are a factor in breeding destructive population of 

 thrips in Alabama, Florida and Georgia. Many peanuts lost at harvest 

 remain in the ground over winter and germinate the following spring. 

 Usually these volunteer plants emerge a few weeks earlier than the regu- 

 lar crop. The thrips multiply on the volunteers and then migrate to the 

 younger plants, where peanuts follow peanuts in rotation. Doubtless other 

 early host plants are also of importance in this respect. 



Much additional information is needed on the biology of the tobacco 

 thrips with emphasis on overwintering habits, succession of host plants 

 in relation to injury to peanuts, and development of the insect on peanuts. 



Control. Heavy rainfall is one of the most effective natural controls 

 of tobacco thrips. This fact was noted as early as 1907 {77). Predaceous 

 insects are also of value in reducing the population. A true bug, 

 Triphleps'^ insidiosus Say, was reported as feeding upon F. jusca {77). 

 The ladybird, Hippodamia convergens Guerin, and a lacewing, Chrysops 



^ The closely related species F. tritici usually pupates in the ground (157). It is possible 

 pupation of F. fusca may occur in the soil as well as on the host plant. 

 ' Onus. 



