UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY 4, CALIFORNIA THE PEA WEEVIL GORDON L. SMITH 1 and E. A. MICHELBACHER 2 The pea weevil 3 is becoming a serious pest of field and canning peas in California. This leaf- let presents some of the latest information on its life history and control. Description and Life History The adult pea weevil is a short, chunky beetle about l/5 inch long. The base color is brownish, flecked with white, black, and gray patches. There is a distinct spot of white scales just back of the head, and another on the exposed tip of the abdomen. The larva, white with a brown head, is legless and grublike. The adults begin to fly into the fields when the peas first start to bloom. They are at- tracted to the flowers, where they feed on the pollen. The elongate, yellow eggs are laid on the very small green pods. They hatch in 5 to 18 days, the time depending upon the temperature. Spines and short legs help the newly hatched larvae to burrow through the pod and into the pea, where feeding and development take place. The entrances thus made are small and very dif- ficult to find. As soon as the larvae become established within the peas they molt, or cast their skins, for the first time. They lose their spines and short legs, and for the remainder of the larval period they are smooth grubs. Two more molts occur. Upon reaching maturity, after 30 to 50 days, the larvae pupate. First, how- ever, they construct a tunnel to the seed coat so that the adults may emerge. After 10 to 15 days the pupae transform to adult beetles, which escape from the peas by cutting through the cir- cular "windows" left by the larvae. The total time of development fx"om egg to adult is 45 to 60 days. Some adults leave the peas during the summer and fall; others may re- main in the harvested and stored peas until the next winter and spring. If harvest is much de- layed, many weevils may emerge from the peas be- fore the threshing. As a result, some of the adults overwinter in the fields and in other pro- tected areas out of doors, while others survive the winter in stored peas. Unlike the bean weevil, this pest is not able to breed in the stored crop. All infestation occurs in the field while the peas are developing. Control of the pea weevil involves sanitary and cultural measures, the use of insecticides and fumigation. For good results, usually, all these factors must be considered. Sanitary and Control Measures Satisfactory results cannot be secured by the use of insecticides alone; proper sanitary and cultural measures must also be taken. All field refuse should be plowed under as soon as the pea crop is removed from the field, and everything in reason done to destroy the weevils hibernating in field borders and elsewhere. Burning the pea stubble has been recommended. If, however, the pea refuse is of value for pasturage, the fields should be pastured off as soon as possible after harvest. Green peas and cannery peas should not be grown in the same areas with seed peas. Seed peas should be harvested as soon as fully ripe. Delayed harvest results in the shattering of many peas and allows the weevils time to complete de- velopment and emerge in the field before thresh- ing. Where seed has shattered, every effort should be made to destroy it before the weevils can emerge. Use of Insecticides Associate in Entomology. Assistant Entomologist in the Experiment Station. Laria pisorum (Linn.) ( Mylabris pisorum , Bruchus pisorum ) . Green and canning peas can be profitably treated against the pea weevil with a dust con- taining 0.75 per cent rotenone. This dust is ap- plied with a ground machine fitted with a cloth hood or apron to prevent drift and insure thorough coverage. From 20 to 30 pounds per acre is re- quired. The first application is usually made within a few days of the time when the peas start to bloom and at 6- to 10-day intervals thereafter. As a rule, three applications are necessary. [1] A standard sweep net may be used to determine the size of the pea-weevil population that has migrated into the field at blossoming time. The largest populations are usually found at the edges of the field, and sometimes control is ob- tained by dusting these borders early while the beetles are concentrated there. In the produc- tion of canning and freezing peas, even low popu- lations of adults may be a serious matter unless control measures are instituted. In the absence of control, investigators have found 5 weevils collected in 50 sweeps of an insect net are likely to indicate a 15 to 35 per cent infesta- tion of dry harvested peas. For canning or freezing peas, 1 weevil in 100 sweeps is usually considered to indicate a serious infestation. Because the pea weevil is greatly influenced by weather conditions, sweeping for population counts should be done at temperatures of 65° F or higher. At these temperatures the weevils are active on the plants, whereas at lower tem- peratures they stay close to the ground. For all peas, recommendations concerning the equipment, material, conditions, and rate of ap- plication are as follows: 4 1. A ground dusting machine, equipped with a canvas or cloth hood at least 25 feet long, should be used. 2. The dusting machine should travel not faster than 4 1/2 to 5 miles per hour. 3. The wind velocity should not exceed 12 miles per hour. 4. A dust containing 0.75 per cent rotenone should be used at the rate of 20 to 30 pounds per acre. Dusts containing 0.75 per cent rotenone cost about 12 cents a pound. At the rate of 20 to 30 pounds per acre, the insecticide cost is $2.40 to $3.60 per acre for each application. Accord- ing to a recent publication 5 on growing field peas, the most effective method of preventing the damage done by pea weevils is fumigation; furthermore, the continuous growth of field peas is almost sure to result in the constant increase of the weevils, and almost the only remedy is to stop growing this crop for several years. At the Oregon Agricultural Experiment Station, however, a single dusting to control the pea weevil on Austrian field peas has been recom- mended because of significant results as measured by improved average germination and quality. Only this one treatment is considered economi- cally feasible; and it should be applied when the greatest number of beetles are present on the vines, at full bloom when very few small pods have set. Even when this treatment is applied, early harvest and prompt fumigation are still necessary. Fumigation of the Dry Peas for Storage The importance of early harvest of dry peas has been emphasized. This measure, however, will be of little benefit unless the peas are fumi- gated immediately after being threshed. Fumiga- tion is necessary to destroy the weevils that may be developing within the peas, and should precede the cleaning and storing. Oregon Agricultural Experiment Station. Sug- gestions for the control of the pea weevil in Oregon for 1939- Circular of Information 200:1-51- 1939. (Mimeo.) 5 McKee, Roland, and H. A. Schoth. Culture and pests of field peas. U.S. Department of Agricul- ture Farmers' Bulletin 1803:1-16. 1938. [2] 5m-4, '44(140)