10 BULLETIN 1243, U. S. DEPARTMENT OF AGRICULTURE. 



devoured. The result is a network of narrow bands of leaf tissue 

 covered by the thin upper epidermis. The feeding habits of the beetle 

 are quite similar to those of the larva in many cases, but usually the 

 leaves are more ragged in appearance. 



The 12-spotted cucumber beetle (Diabrotica 12-punctata Oliv.) 

 feeds very similarly in many cases, as do also certain small cater- 

 pillars. 



In territory where the bean beetle is not numerous, specimens of 

 suspected insects should be taken for identification before the 

 presence of the bean beetle is reported. 



After the larva has molted three times the fourth larval instar or 

 stage appears. Feeding by the larva in this stage is very destruc- 

 tive, a single larva being able to destroy a large bean leaf in one day. 

 After feeding for from 4 to 6 days in moderately warm weather the 

 larva attaches itself by means of an abdominal pad at the posterior 

 end and remains "quiescent for about 2 days. A fourth larval molt 

 then occurs and the pupa stage is assumed. The larval skin, which 

 is white in color, remains attached to the yellow-colored pupa (PI. 

 II, B; PL III ; PI. IV, D) , covering the posterior abdominal segments 

 and holding the pupa to the leaf or other object. Late in the fall the 

 pupal skin is often black in streaks and sometimes completely black. 

 Under conditions of severe infestation, pupae occur on various plants 

 and objects near destroyed plants. Egg masses are also deposited 

 on such plants as mustard, cocklebur, and certain weeds, on which 

 the hatching larvae would starve. 



The adult or beetle emerges from the pupa in from 6 to 8 days. 

 Immediately on emergence it is light lemon-colored and very soft. 

 In a few hours the spots on the wing covers appear. The wings are 

 protruded backward from under the elytra or wing covers, extending 

 a distance almost the length of the body. At the end of 24 hours the 

 adult becomes fully developed and quite hard, but the color is light 

 lemon, with black spots, and dark mouth parts, undersurfaces, and 

 appendages. With age the color becomes darker, approaching 

 copper color to brown in overwintered specimens. 



Newly emerged adults (PI. IV, E) usually remain on the bean 

 plant and feed before taking flight. Food is not essential, however, 

 and in cases where fields are destroyed newly emerged beetles fly 

 away in search of food. 



The fecundity of the insect under favorable circumstances is re- 

 markable. During the summer of 1921 many fields of beans about 

 Birmingham, Ala., were so heavily infested that the general appear- 

 ance of the crop resembled the effect of a severe drought. Scattered 

 over the remains of the plants, the ground, weeds, and any object 

 were thousands of pupae and larvae, so numerous as to give a yellow 

 tone to the field. Larvae and beetles feed on pods and stems under 

 such conditions. 



The total life period from egg to adult covers from 25 days during 

 the heat of summer to 58 days in early spring, the usual minimum 

 being 27 days during summer, and the usual maximum during the 

 spring and fall being about 44 days. From 6 to 29 days additional 

 are required between emergence of the female from the pupa and 

 egg deposition. The average preoviposition period for 32 females in 

 two different seasons was 11.5 days. Table 3 gives a brief summary 

 of the life history at Birmingham, Ala., for the years 1921 and 1922. 



