MEXICAN" BEAN BEETLE IN THE SOUTHEAST. 



Table 2. — Eggs laid by 69 females of the Mexican bean beetle for which records 

 are complete, 1921 and 1922. 



Generation. 



Overwintered generation. 



First generation 



Second generation 



Third generation 



Number 



of 

 females. 



number 



of eggs per 



female. 



507 



708 



1,272 



413 



Number 



of 

 females. 



Average 



number 



of eggs per 



female. 



252 

 286 

 479 

 422 



Average for 69 females (two seasons) 459 



Some females laid no eggs and others only one or two groups, but 

 these are included in the above averages. The average for all females 

 as given is probably low, for in nature some of the overwintered 

 females may have deposited eggs the preceding fall, and some of the 

 third and fourth generation females, and a very small number of the 

 second generation, might have deposited eggs the ensuing spring. 



Of 15,804 eggs laid in cage tests in 1921, 46.7 per cent hatched. 

 Of 7,024 eggs deposited in 1922, 52.5 per cent hatched. The lower 



Eercentage in 1921 was due in part to the very low percentage of eggs 

 atching which were laid during the high temperature of August. 



The Mexican bean beetle is polygamous. A single fertilization of 

 the female is sufficient for the production of as many as 10 groups of 

 fertile eggs, even though five months or more passed in hibernation 

 intervene between mating and the first egg deposition in the 

 spring. (See Table 1.) Gravid females may thus enter hibernation 

 and without further intervention of the male deposit fertile eggs in 

 the spring. The beetles always feed on foliage in the spring before 

 oviposition. 



The young larvae hatch from the eggs after from 5 to 14 days, 

 depending upon temperature conditions, the average incubation 

 period at Birmingham, Ala., during June, July, and August being 

 6 days. Hatching of all eggs in a group usually occurs within 24 

 hours. The newly hatched larvae leave the eggshells and cling to the 

 tips of the eggs, completely covering the shells. They begin to feed 

 soon after leaving the eggs, many of them reaching the leaf and feeding 

 while clinging to the eggshells about the edge of the group. A very 

 thin layer of epidermis is eaten. After a day or so the larvae begin 

 to scatter and feed more heavily, devouring thicker portions of the 

 leaf. By the time of the first molt they have scattered over several 

 leaves. As they grow older they feed heavily and more rapidly 

 and scatter over the plant or adjacent plants. In the third and fourth 

 larval instars the most serious damage is done to the crop. 



The larvae (PL IV, C) remain on the plant on which they have 

 hatched, or on adjacent plants. While capable of crawling a con- 

 siderable distance under adverse conditions, as much as 24 feet in 20 

 minutes, migrations do not usually occur except prior to pupation 

 when sufficient protection is not at hand. 



The larva's method of feeding is characteristic of the species. 

 (PL V, A, B.) It consumes a narrow band of the leaf and usually 

 leaves the upper epidermis intact. It then moves and consumes 

 another strip, and so on until several such parallel strips have been 



