14 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
Thrips are in the ground all of this time, and for the most part within | 
reach of the cultivator, but they mature and arrive on the trees in 
March and April, before spring cultivating is begun. 
NATURAL ENEMIES. 
if The pear thrips is largely protected from ordinary preaaceous and 
| parasitic insects, because it spends so long a time hidden away in the 
| ground. A successful parasite must in a way parallel the life of its 
| host, and we have found no insect which thus follows the pear thrips. 
Raphidians, or snake flies, their commonest enemies in the Santa 
Clara Valley, feed rather on the younger forms than on the fully 
developed insects, and they do not 
appear early enough in the spring 
to constitute an effective check to 
the pest. To be competent thrips 
killers they would have to feed on 
other insects for perhaps ten months 
in the year and then, when thrips 
appear, suddenly change their diet 
and later, after thrips have gone into 
the ground, as suddenly change back 
again to aphides or to something 
else. Such feeding habits are not 
to be expected in a vredaceous 
species. | 
Ants were at one time thought to 
be doing much good as an enemy of — 
the thrips. A certain orchardist @} 
brought in an ant with a thrips 
impaled in its jaws—the evidence | 
: complete. After a careful investi- | 
iI EES eS ee UNS 2 ees ie) nee gation, however, it was found that | 
thrips: a, active fruiting stage or adult ? d > | 
| thrips; 6, branching mycelia; c, forming only avery. small percentage of ants > || 
: ee Roe ee ge ® © highly were actually killing thrips. Four | 
hundred ants were examined as 
| they descended a thrips-infested tree. Twelve of these carried 
| something in their jaws and only 4 of these objects were thrips. Thus — 
I only 1 per cent of the ants on the tree were actually killing thrips — 
| and carrying them down. It has been a common observation among — 
orchardists, however, that thrips are not common where ants are © 
| unusually abundant. 
Spiders and mites are active enemies of thrips. In some of our — 
breeding cages almost all of the thrips would at times be killed by 
il some small spider or mite which had gained an entrance. The writer 
| has observed ared mite (Rhyncholophus sp., determined by Mr. Nathan — 
| Banks) actively engaged in feeding on the onion thrips (Thrips tabaci — 
