No.isio. NORTH AMERICAN THYSANOPTERA— HINDS. 119 



by the presence of Thrips, as their action would tend almost entirely 

 to self-fertilization of the flowers, which Nature does not generally 

 approve. Therefore I believe that their value in this wa}^ must be 

 very limited. 



NATURAL CHECKS. 



Insects and Acari^ etc. — The most important insect enemy appears 

 to be Trl'plileps insidiosus Say, which is very common on flowers and 

 ma}^ often be found with a Thrips impaled upon its rostrum and 

 held in the air while the captor sucks the juices from the l)ody of its 

 victim. The eggs of TripJdeps are laid in a similar manner to those of 

 Thrips and the larva? of the former also prey upon the larvte of the 

 latter. The length of the life cycle of Trlphleps is about the same as 

 that of Thrips. Megilla macidata also devours Thrips in great num- 

 bers when both arc aliundant. Chrysopa and Sipphus larva? have 

 been found feeding upon the larva? of Thrips taljaci. Heeger has 

 recorded Scymnus ater^ GyrojpTmeim manca^ and some fly lar^'te as 

 preying upon them, and Uzel has found TrlpTdeps inimdn also. 



1 have frequently found Anaphotlirlps striatus bearing one or more 

 small, scarlet Acari (probably the larva? of a Tromhidiwn) attached to 

 some membranous area of the body. 



Both I'^zel and Quaintance have found the eggs and adults of Nem- 

 atode worms in the Iwdies of Thrips, Uzel recording over 2()0 worms 

 from one specimen. 



riant pximsltes. — Thaxter (297) has taken Empusa {Entomojyhthora) 

 spliaerosperma Fries from a species of Thrips which it was destroying 

 in larval, pupal, and adult stages. Pettit has found in Michigan 

 another parasite which he thinks will prove to be a Gregarinid (464). 

 It was most abundant in the moist breeding cages, causing the insects 

 to die and turn black. I have rarely found a fungus growing in a 

 dead specimen which appears to be a species of 2facrosporlum, but it 

 was not possible to tell whether the fungus caused the death of the 

 insect or came m later. 



Rahi. — Of all the natural checks, none can compare in efiiciencv 

 with a hard dashing rain. It has been noted that Thrips tdbaci and 

 Anaphothrips striatus, which become extremel}' abundant during hot, 

 dry weather, disappear almost entirely as soon as the heavy showers 

 of midsummer begin, and as long as such showers continue at frequent 

 intervals the Thrips do not again become abundant. The same result 

 will probably be found true in most outdoor leaf-inhabiting species. 



ARTIFICIAL CHECKS. 



These fall naturally into two groups, insecticides and cultural 

 methods. 



Insecticides. — So far as we know, no attempts to control Thrips by 

 means of insecticides have been made outside the United States. Here 



