296 



THE MONTHLY BULLETIN. 



The adult insect is one of the snout beetles, or Rhyncophora belonging to the 

 same family with the apple curculio and plum eurculio of the Eastern States. It 

 is about three-sixteenths of an inch in length, grayish brown in color, and possesses 

 a comparatively long snout. The adult alfalfa weevils pass the winter on the ground 

 in rubbish and in crevices in the soil. In the spring when the alfalfa begins to grow, 

 they come out of their hiding places and begin feeding upon the tender alfalfa shoots. 

 Feeding takes place through the long snout, with which it punctures the alfalfa stems 

 for the purpose of sucking out the plant juice. After feeding for several days or 

 weeks during the early spring, egg-laying begins. The adult female accomplishes this 

 by boring a hole into the alfalfa stem with her snout, after which she turns and 

 deposits the eggs into this cavity. The eggs are very tiuy, golden yellow in color and 

 oval in shape. They are laid in clusters, five to forty in a mass. 



The eggs hatch in a few days, the incubation period depend 'ng of course upon 

 conditions of temperature and humidity. The newly-hatched larva is pale green, 

 almost yellow in color, with a black head. It soon leaves the egg cavity in the alfalfa 

 stem and crawls up to the tender growth at the top of the plant, where it 

 can feed in hiding. In a few days the first molt takes place, the larva now becoming 

 a darker green in color and of course larger in size. In the succeeding molts it 

 gradually increases in size and feeding capacity, and a faint pale stripe appears run- 

 ning down the middle of the back. After feeding for a month or so it becomes full 

 grown, increasing about a quarter of an inch in length. The larva feeds almost 

 entirely on the tender portions of the host plant, in this way preventing it from 

 making any appreciable growth. When the larva or grub has become full-fed, pupa- 

 tion takes place. This generally occurs at the base of the plant in the old stems and 

 rubbish usually found there, although it frequently pupates within a curled leaf. 

 The pupa is contained in an extremely delicate, lacy white cocoon, through which 

 the contents may easily be discerned. It is pale green in color, gradually becoming 

 darker until just before it changes into the adult beetle, when it takes on a brownish 

 tinge. 



The greatest damage resulting from the presence of this insect occurs in the first 

 and second crops. The first crop usually succeeds in making a start in the spring, 

 before the young larvae are abundant. However, the alfalfa stems are soon filled 

 with eggs and the larvae hatching from these eggs before the crop is cut, sometimes 

 cause a total loss. The second crop will usually be a total loss if nothing is done, 

 since the abundant larvae found on the first crop at the time of cutting fall to the 

 ground and overwhelm the new shoots of the second crop 

 so that it is entirely prevented from growing, and the 

 field remains as barren as though the alfalfa had been 

 suddenly killed. The damage in the infested districts 

 has been estimated at 50 per cent of the entire second 

 crop, where l-emedial measures are not undertaken. 



CONTROL MEASURES. 



For the control of the alfalfa weevil a number of 

 different methods have been devised by the U. S. Depart- 

 ment of Agriculture and the Utah Experiment Station. 

 Since the adult weevils spend the winter on the ground 

 and in the crevices in the soil, a large number may be 

 destroyed by flooding the fields during late winter and 

 early spring with muddy water. This method, however, 

 is applicable only under special conditions of water 

 supply and soil. The thorough cultivation of the alfalfa 

 fields in the spring by means of discs, spring-tooth 

 harrows or other special machinery is of great value in 

 stimulating the growth of the crop and keeping it well 

 ahead of the feeding weevil larvae. In many cases this 

 cultivation was found by the Department of Agriculture 

 to increase the first crop fully 50 per cent. Spraying 

 the fields when the plants are small with a stomach 

 poison, such as arsenite of zinc, will destroy large num- 

 bers of the weevils before they lay their eggs in the 

 spring. When properly done there is no danger to live 

 stock in using this method. Pasturing the fields with 

 live stock is useful in early spring, since the animals eat the stems containing the 

 weevil eggs. The Department of Agriculture is authority for the statement that 



Fig. 

 cocoon 



95. — Alfalfa weevil 

 much enlarged. 

 During this stage the pres- 

 ence of the weevils is com- 

 paratively easy to detect. 

 The cocoons are pure 

 white and are usually 

 Found in the curl of a leaf, 

 at the base of the stem or 

 in other protected places. 

 (U. S. Dept. Agr.) 



