116 APPLIED ENTOMOLOGY 



everywhere east of the Rocky Mountains where the potato is grown and 

 it has also reached the Pacific Coast. It does not apparently thrive 

 in the hot climate of the more southerly States. 



The adult beetle (Fig. 1066) is somewhat less than half an inch long 

 and about two-thirds this width, its back rather high and rounded. It 

 is clay-yellow and has 10 longitudinal black lines on its elytra. The head 

 has a black spot above, and the pronotum has a number of irregular spots. 

 Winter is spent as the adult in the ground but the insects come out quite 

 early in the spring. As soon as the potatoes are up, they begin to feed 

 and soon lay their eggs, placing these on the under surface of the leaves 



t . in small clusters, an individual, lay ing 500 



or more in all. They are small, yellow 

 e &g s wn i cn hatch in from 4 days to a week 

 or more, according to the temperature. 

 ^ e S ru bs or "slugs" as they are often 

 called (Fig. 106a) are dull brick-red, soft 

 and with fat bodies. They feed for from 



a b 2 to 3 weeks, then go into the ground 



FIG 106. Colorado Potato wnere they pupate for a week or two, after 



Beetle (Leptmotarsa decimhneata 



Say), slightly enlarged: a, full- which the adults emerge and lay eggs for a 

 grown larva (Grub); adult Beetle. sec ond generation, the adults of which ap- 



(From Berlese, After U. S. BUT. & . ' 



Eut. Cire. 87.) pear early in the fall. This second gen- 



eration of beetles feeds for a time, then in 

 September or October enters the ground to pass the winter. 



As the eggs of this insect are not all laid at one time, different ages 

 and different stages even, may be found together in the same field. And 

 as the adults feed in the spring during their egg-laying period, as do the 

 two generations of adults produced during the season, in addition to the 

 two generations of grubs which also consume the leaves, the plants are 

 being attacked much of the time. 



While the potato appears to be the preferred food of this insect, other 

 members of the nightshade family are sometimes attacked, particularly 

 the tomato and eggplant. 



Control. This pest is easily controlled by spraying with either 

 of the stomach poisons and as the potato is quite resistant to poisons, the 

 strength of the mixture can with safety be somewhat increased above 

 that of the standard formula. The chief difficulty in control is that as 

 the beetles attack the rapidly-growing plant as soon as it appears above 

 ground, the spray should be applied then, while a week later a large 

 amount of new growth which has no poison on it will have developed, 

 upon which the insects can feed. To avoid this, spraying during the 

 period of rapid growth needs to be done more frequently than is the case 

 with most plants. Two or three treatments, however, will generally be 

 sufficient, and a combination with Bordeaux mixture is advantageous 

 where arsenate of lead is the stomach poison used. 



