84 



THE PRACTICAL ENTOMOLOGIST. 



Notes on DORYPHOEA 10-LINEATA. Say. 

 (The Ten-striped Spearman— " Potatoe Bug.") 



BY IIENUY SHIMEn, M. D. 



This very destructive insect to the potatoe crops 

 is malving its appearance in groat numbers. Their 

 first appearance was about the 20th of May, and 

 now the handsome insect may be seen every day, 

 slowly flying around in Cjuest of food and breeding 

 grounds. 



Last summer I conducted a series of thorough 

 investigations of the nature and habits of the insect, 

 commencing on the 18th of June and continuing 

 throughout the season, malting a daily record of all 

 that I saw as I bred them through from generation 

 to generation ; during a portion of this time I was 

 feeding several hundred together. 



A few of the more important results may be brief- 

 ly enumerated as follows: — 



From an equal number of males and females, 

 well fed and made as comfortable as possible in 

 confinement, I obtained an average of 719 eggs to 

 each female ; but in the fresh, pure air, sunlight 

 and freedom of nature, under propitious circum- 

 stances I have no doubt of its exceeding a thou- 

 sand. 



They laid some eggs every day for forty days, 

 commencing July 15th, and ending on the 1st of 

 September. The smallest average was in the first 

 part of this time, being 7* eggs per day to each fe- 

 male; the greatest average was about the middle 

 of the time,75 eggs ; the last day they averaged 12 J 

 eggs. 



The eggs, as all who have seen them well know, 

 are laid ou their ends on the leaves of the potatoe 

 plant, in somewhat regularly arranged, rather loo.se 

 clusters, and sometimes in two tiers; they are yel- 

 low, elipsoidal, .08 inch by .04.5 inch in diameter; 

 they hatch in about six days. The young, sluggish 

 larva is at first mostly black ; abdomen, dirty brown; 

 it feeds voraciou.sly, and in a few days becomes of 

 a lighter color. At the end of seventeen days the 

 full grown larva ceases eating, when it measures .5 

 inch by .25 inch in diameter ; the abdomen being 

 much the largest part, the thorax being only .15 

 inch wide, having increased its volume 200 times, 

 or near twelve times its original weight daily, and 

 moreover is so solid as to sink in the water; from 

 these dates, it is no difficult task to apprehend its 

 eating capacity. 



/ At this time, as is well known to many, the head, 

 posterior half of thorax, legs, and two rows of vitta 

 on each side of the abdomen are black, the ante- 

 rior half of the thorax yellow. Abdomen, large, 

 tumid, orange, wrinkled, with a transverse groove 

 on each segment; it uses the tail to aid in locomo- 

 tion. 



When touched, so as to produce alarm, it curls 

 up into a ball and plays "possum." 



After the seventeenth day, it disappears beneath 

 the ground, if accessible ; but if kept in an empty 

 box, it lies on its back, where the process of trans- 

 formation may be readily observed; as it lies on its 

 back, in from three to five days it casts its last pu- 



pa skin by throwing it off upwards and backwards, 

 slowly pushing it off mostly by the muscular writh- 

 ing movements of its tail; it gradually becomes 

 shortened in this operation, and assumes the pupa 

 state, during which condition it only moves its tail, 

 but that freely, being otherwise entirely helpless. 

 The wings may now be seen developing, downward 

 and backward, beneath the pupa skin. In tea 

 more days, or thirteen days in all after it has ceas- 

 ed eating, and if permitted to enter the ground, the 

 imago appears, being just one month from the time 

 of hatching. 



Thus in thirty-six days from the laying of the 

 egg, the perfect insect appears, at first of a very 

 pale light yellow color, the stripes but faintly per- 

 ceptible, in about six hours the colors become 

 bright and perfect, and the insect immediately be- 

 gins to eat. The shell is at first comparatively soft, 

 but continually grows thicker and firmer during its 

 life, from the perpetual accretion of .solid matter. 



If permitted to transform in its natural position 

 in the compact earth, as may be seen at the bottom 

 of an earthed breeding-box, they all mature in pre- 

 cisely the same time, but more perfectly, none ap- 

 pearing with shrivelled wings, &c., as many in 

 empty boxes did. 



In about seven days the imago begins to pair, 

 and at about the fourteenth day, on an average, be- 

 gins to lay its eggs; thus in fifty days after the egg 

 is laid the offspring begins to propagate, so that the 

 first of the spring brood becomes fertile about the 

 10th of July, the second generation about the 1st 

 of September, and the third and many of the last 

 developed of the second, passes the winter in the 

 pupa state in the ground, and in the following 

 spring appears in the perfect state, from the middle 

 of Jlay to the early part of June, and in a few 

 days, as we have seen above, begins to lay its eggs, 

 and continues for forty days or more, or until the 

 first laid begin to propagate, so that we have them 

 of all sizes during the sumluer. 



An imago developed in midsummer lived twelve 

 days after its development without eating any food; 

 one developed October 1st, lived until midwinter. 



Those that laid the eggs above noted, became 

 more sluggish thereafter, and ate much less. I 

 supplied them with fresh potatoe tops daily, during 

 the month of September ; towards the last of the 

 time they ate but little if anything. I kept them 

 in a box during the winter, with a supply of pota- 

 toe tubers, but did not observe them eating any- 

 thing. They passed the winter in a kind of semi- 

 dormant condition, producing motion only when 

 disturbed ; they remained alive until the 1st of 

 March, when they were accidentally expo.sed to 

 cold sufficient to freeze the potatoes that were in 

 with them. Soon after this 1 found them dead, of 

 which accident I was very sorry, for from appear- 

 ances I was hoping to keep them over till another 

 summer; at all events it was very remarkable that 

 they should have lived so long after the termina- 

 tion of the egg-laying season. 



Regarding the natural means for their destruc- 

 tion with our present knowledge, the prospect is 



