8 MASS. EXPERIMENT STATION BULLETIN No. 285 



food, or they may swallow it after it has stuck to their mouth parts while they are 

 crawling over the fruit and foliage in search of a suitable place to feed. When 

 feeding is greatly reduced, as it is by low temperatures, the small amount of 

 arsenic obtained may act as a temporary stimulant rather than a toxin, and the 

 result is not fatal until an accumulative poisoning is built up by continued small 

 doses. At a constant temperature of 55° F., several beetles lived from 25 to 27 

 days with only poisoned fruit for food, while at 75° F. the maximum number of 

 days that beetles lived on similar poisoned fruit was 7 to 10 days. 



When high temperatures stimulate feeding and egg laying so that the beetles 

 make several punctures per day, the greater amount of poison obtained from 

 these several punctures causes death in a proportionately shorter time. In one 

 experiment 10 beetles at 55° F. lived 10.6 days and made an average of 4.1 punc- 

 tures each during their life; while another group at 65° F. averaged 4.2 punctures 

 each but lived only 5.4 days because the punctures were made in a shorter period 

 of time, and a much greater amount of poison was obtained before the natural 

 resistance of the insect could overcome the toxic effect produced. 



LABOR.\TORY EXPERIMENTS WITH PLUM CURGULIO BEETLES 



FEEDING ON POISONED FRUIT AT CONTROLLED TEMPERATURES 



Lead Arsenate at Different Concentrations 



A summary of the records from 2 cages of 10 beetles each, confined in the 

 constant temperature cabinets with fruit sprayed with lead arsenate showed 

 that the average number of days which the beetles lived decreased consistently 

 with each increase of 10 degrees in temperature from 55 ° F. to 85 ° F. The great- 

 est decrease in length of life was between 55 ° F. and 65 ° F. Table 5 also shows 

 that the average number of days which the beetles lived decreased consistently 

 with the increase in concentration of lead arsenate from 3 pounds to 5 pounds 

 in 100 gallons of water. However, the decrease in length of life in favor of 5 

 pounds of lead arsenate compared to that where 4 pounds was used is so little 

 that it is doubtful if the slightly better control is worth the cost of an additional 

 pound of poison. When lead arsenate was increased to 6 pounds in 100 gallons 

 of water, the length of life of the beetles increased at three of the four tempera- 

 tures over that when 5 pounds of lead arsenate in 100 gallons of water were used. 

 This may indicate that concentrations of lead arsenate greater than 5 pounds in 

 100 gallons became repellent to the plum curculio, and they may live longer when 

 feeding on fruit sprayed with 6 pounds of lead arsenate in 100 gallons of water, 

 because they do not feed on such fruit as quickly or as readily. Similar action 

 has been reported by Stellwaag (8) in Germany who found materials with 15 

 per cent arsenate more repellent and consequently less effective against silk- 

 worms than those containing 10 per cent of this poison, and bj' Crumb (1) who 

 states that in experiments with poisoned bran baits, "a dosage of 1 pound of 

 Paris Green to 24 pounds of bran is rather repellent to cutworms, while a bait 

 with half this concentration of poison is scarcely at all repellent." 



Lead Arsenate Plus Other Materials 



With 4 pounds of lead arsenate and 1 pint of fish oil in 100 gallons of spraj-, 

 the average life of the beetles was only slightly less than where fish oil was not 

 used, indicating that the fish oil has little, if any, repellent or inserticidal action 

 against the plum curculio. However, fish oil is an excellent agent for spreading 

 and sticking the lead arsenate in an even film over the fruit and for preventing 

 the poison from weathering and washing off too rapidly. 



