350 ANNUAL REPORT SIVOTHSONL^N INSTITUTION, 1940 



short time the females deposit yellow e^gs in groups of from 40 to 60 

 on the underside of the bean leaves. One female has been known to 

 deposit over 1,500 during one season, and the average is nearly 500 

 per female. The time required for the development of the insect from 

 egg to adult varies with the climate. The eggs may hatch in from 5 

 to 14 days, the larva requiring 15 days to 3 weeks to complete its 

 development. In the pupal stage the insect may remain for a week 

 or 10 days. There is no clear-cut line between generations and a!l 

 stages of the pests may be found in the same field at the same time 

 during the summer season. In the South there may be from two to 

 four generations ; in Ohio one or two generations may develop during 

 the season. The beetles which have overwintered usually live until 

 early summer. 



The adult beetles are sluggish as compared with many of the insects 

 encountered in a bean field. They crawl rather slowly and are not 

 easily disturbed. At certain times of the year, however, many of 

 the beetles take wing and in some cases fly high into the air and soon 

 disappear from sight. In August the beetles become particularly 

 restless and at this time the greatest dispersion takes place. Flight 

 experiments conducted with a large number of marked beetles have 

 shown that the insect will travel as far as 5 miles in 2 days and that 

 movements of 31^ miles in the same length of time are not unusual. 

 Considering the facts that over a period of 20 years only a few isolated 

 infestations of the beetle have been found in the East and that the 

 general movement has been in a northeasterly direction from the 

 original infestation, the indications are that the spread has resulted 

 from flight, probably aided by wind currents. 



Nature of injury. — The injurj'^ caused by the adult and larva of 

 the bean beetle to the foliage of the bean plant differs from that 

 caused by any other insect that utilizes the bean as food. The adult 

 feeds, as does the immature form, on the lower surface of the leaves, 

 eating ragged areas in the leaf, but often cutting through to the upper 

 surface, giving the foliage a lacelike appearance. The larva, on the 

 other hand, feeds entirely on the under surface of the leaves and does 

 not cut through the upper epidermis. Dr. Neale F. Howard de- 

 scribes the feeding of the beetle larva as follows : The mandibles are 

 used alternately in scraping the tissue from the leaf between the 

 veins. At intervals the mandibles meet and compress this loosened 

 tissue, which remains on the leaf as small "windrows" or strips. 

 As the plant tissue is compressed the larva apparently ingests the 

 sap or plant juices and discards the more solid portion. When an 

 infestation is heavy, the plant is practically destroyed and has the 

 appearance of having been scorched by fire. 



Natural e^iemies. — Apparently none of the insect parasites and 

 predators of the bean beetle followed it from its original home into 



