BIOLOGY 



IV. RESPONSES OF BRUCHUS TO MODIFIED 

 ENVIRONMENTS 



J. K. Breitenbecher 



From the Dept. of Zoology, University of Okla., Contribution 



No. 31, Second Series. 



Introduction. 



The common occurence of the four-spotted cow-pea weevil 

 (Bntchus quadrimaculatus) , was early discovered in the tropical 

 and sub-tropical countries, where the climatic conditions are 

 especially favorable for its development. No comprehensive study 

 from the standpoint of the environmental effects of temperature 

 and humidity upon the insect have been attempted. 



The original home of this insect is very much in doubt, for 

 it was noted at widely different localities at about the same time. 

 The earliest record of its presence in the United States seems to 

 have been made by Oliver in 1795, who reported it from Carolina. 

 But Fabricius first described the' species in 1792 and records it 

 from Santa Cruz, West Indies. Chittenden states that this insect 

 is probably of foreign origin, having been carried to the United 

 States with its favorite food plant. Very little attention was 

 given it by entomologists until the early nineties. 



Life History. 



This species has four stages in its life cycle ; adult, egg, larva 

 and pupa. The length of the egg stage depends very much upon 

 the temperature and the hardness and dryness of the cow peas. 

 Experiments have shown that it may vary from 3 to 21 daj^s. On 

 hatching the young larvae bore their way into the seed where they 

 feed until becoming pupae. The larval stage may vary from 1 to 

 42 days, depending upon the environment, chiefly temperature. The 

 transformation from larvae to pupae occurs within the larval bur- 

 row. At first the pupae are white but after a few days they 

 change to a light tan color. The adult emerges by rotating its body, 

 thus cutting a circular plate out of the seed coat. 



It has been shown that at 100° F. the entire life cycle may 

 be completed in 19 days and 90° F. gives a generation every 20 

 days, but 100° F. is the optimum for genetic researches. 



