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VOL. XXIV. LONDON, AUGUST, 1892. No. 7. 



THE FIRST LARVAL OR POST-EMBRYONIC STAGE OF 

 THE PEA AND BEAN WEEVILS 



BY C. V. RILEY, WASHINGTON, D. C. 



In No. 9-10, Vol. IV., of " Insect Life," an account was given of the 

 post-embryonic larva of the Bean Weevil, attention being called to some 

 most interesting characteristics of this larva, which is possessed of 

 temporary thoracic legs and some other structures which admirably serve 

 its locomotive needs until it has entered the bean, when, with a cast of 

 the skin, they are lost and the larva assumes the ordinary apodous form of 

 weevil larvse. The Bean Weevil ( Bruchus fabae, Fitch [Riley],) goes on 

 breeding in stored beans, in which respect it differs from the Pea Weevil, 

 as also in the fact that a number of individuals, owing to their smaller 

 size, will develop in the same bean, as many as twenty-eight having been 

 found in a single bean. The eggs are primarily laid upon the bean-pod 

 in the field but chiefly, if not entirely on those which are already mature 

 and ripening, and the larvae enter the same very much as does the Pea 

 Weevil. But whether laid upon the pods in the field or laid upon the 

 stored beans, the newly hatched larva has to eat its way into the bean 

 and it is able to move about quite briskly by the aid of these temporary 

 legs. Four rather stout but short spines or spurs on the prothoracic 

 shield and four smaller spurs on the anal plate facilitate the penetration 

 of the smooth and rather thin skin of our ordinary beans. The temporary 

 legs are curious in appearance, consisting of three joints, the second long 

 and slender and doubtless corresponding to the fused femur and tibia. 

 The third, which corresponds to the tarsus, is slender and broadened at 

 the tip into a flat pulvillus bearing at the heel a single delicate spur. 



Having recently ascertained these facts upon more careful study of 

 the habits of the Bean Weevil, I was curious to learn whether or not the 

 Pea Weevil (Bruchus pisi, Linn.,) had similar structures in its newly- 

 hatched larval condition. It has long been know that the egg of the Pea 

 Weevil is laid on the outside of the pod, being fastened thereto, and the 



