NO. 1310. NORTH AMERICAN TIIYSANOPTERA— HINDS. 165 



sition soon begins, and lasts for from four to six weeks in many cases. 

 They seem to oviposit as readily at night as in daylight. The deposi- 

 tion of an Qg^ requires about one and one-half minutes. The eggs may 

 be readily seen in the leaf by holding it before a light, when they appear 

 as small, lighter spots; they may be easily separated from the leaf by 

 stripping off the epidermis. The length of the egg stage varies from 

 ten to fifteen days for the iirst generation to from four to seven days 

 during the heat of summer. 



The length of the larval stage varies from two weeks in early spring 

 to about four days in midsummer. The mature larv^ select secluded 

 places in which to transform and are hard to find in the field, but it 

 appears that the}^ usually go down to the basal leaves near the root or 

 into the sheaths higher up the stem. The pupal stage is longer for 

 the long-winged females than for the short, in the former requiring 

 four or five days in early spring, whereas the short-winged form 

 requires only from two to three daj^s at the same season. As the 

 weather becomes warmer they transform more rapidl3^ The appear- 

 ance of a number of winged adults early in Ma}" marks the maturity 

 of the first generation, but as the length of the period of oviposition 

 exceeds the length of time required for the early stages, there is no 

 distinct line between the generations out of doors after this time. 

 The length of the life cycle is from about twelve to thirty days. 



Common name. — Since Professor Comstock's first mention of the 

 injury done by this species of Thrips to June grass and timothy, sev- 

 eral economic entomologists have referred to the most conspicuous 

 effects of its work, the dead tops of these grasses, as "Silver top" or 

 " White top." Man}' have questioned the agency of Thrips in produc- 

 ing this injury and have ascribed it to some other suctorial insect, but 

 the majority of writers are now inclined to credit Thrips with a large 

 part, if not all, of this damage. As they had no means of identifying 

 the little pest, they have usually referred to it as the "Grass Thrips." 

 This name has been very generally used for this species and for no 

 other, so far as we can learn. It therefore appears to be the gener- 

 ally accepted common name. 



Economic notes. — Extensive injuries to grass have been reported 

 from the New England States, New York, southern Canada, Ohio, 

 northern Illinois, and Iowa. Without dpubt the insect causing this 

 damage infests a larger territory than this, for it is so small that 

 it easily escapes ol)servation, and the damage done by it is often 

 attributed to other agencies. In southern Maine, Professor Eernald 

 reported (253) that by haying time one-fourth of the June grass {Poa 

 2)ratensis) in the fields was dead and worthless. In 1887 it produced 

 great injury around Emmet, Ohio, where 30 per cent of the grass was 

 killed (272). In 1888 and 1889 widespread injury was reported from 

 New York (291) and Ontario (322), where it appeared to work most 



