390 THE MONTHLY BULLETIN. 



developing fruits in the same way that the citrus thrips does. One 

 can find thousands of this same species of thrips in the flowers around 

 the potato fields. It is evident that the insects are often driven to 

 attack the foliage of the potato plants by the plowing under of the 

 flowers in the fields before planting. Moreover, most potato fields have 

 many wild flowers all around them, which furnish recruits for the 

 armies of these pests. 



These thrips are very small, about 1 mm. (one-sixteenth of an inch) 

 long, and live by sucking out the sap from flower parts or leaves. The 

 mouth is adapted for piercing a tiny hole through the surface of the 

 leaf and drawing out the sap. The insect moves along, piercing the leaf 

 in many places as it goes. It is by this continual piercing and irritat- 

 ing in so many places by the insects that the leaf is caused to curl and 

 wrinkle. In its efi^ects this injury resembles very much that caused by 

 certain mites, or so-called red spiders, and also the injury by the peach 

 leaf curl fungus. 



The insect in all its young stages is wingless, as are all other kinds 

 of thrips. The color is usually a pale greenish yellow, becoming a 

 little darker when the insects are mature. To the naked eye they are 

 visible as small, actively moving creatures, quickly running about or 

 hiding in crevices and under hairs of the leaf. There are often a very 

 large number of the insects on a single leaf, many of which are not 

 easily visible to the eye because of their small size. Examined under 

 a microscope the larva is soft bodied, with a small head, a long thorax 

 and a long tapering abdomen of ten segments. The body surface has 

 many minute spines on it, especially on the dorsal surface of the abdo- 

 men and on the legs. The antenna are very short in the young larva, 

 becoming longer and possessing more segments as the insect grows 

 older. The body surface of the older larva is in some places shagreened 

 or reticulated. 



The adult is very slightly larger than the mature larva, a little 

 darker in color and not so soft-bodied. In shape of body it very much 

 resembles the larva, but is a little more robust and relatively broader 

 and thicker, and possesses two pairs of long, slender wings with con- 

 spicuous fringes of hairs. The eyes are larger and the antemife longer, 

 and having more segments. The reproductive organs are fully devel- 

 oped and the genetalia are visible at the end of the abdomen. 



The adults have the power of springing very quickly, which they 

 are quite apt to do when the leaf is disturbed. For this reason, to- 

 gether with the small size of the insects, it is very difficult to see the 

 cause of injury to the leaves. They can fly for short distances and 

 thus migrate from place to place. 



The nymph, or quiescent stage, is intermediate between the larva and 

 adult, and is the stage of the life cycle in which the adult organs are 

 being formed. The insect passes this stage in the ground, under the 

 dead leaves, or in crevices and cracks of any kind close to the plants. 



The life cycle of this insect is very short. The eggs hatch in less 

 than a week and the larvae mature in about a week after hatching from 

 the eggs. The nymph lasts only a few days and then the adult, winged 

 insect appears and in a few days begins to deposit eggs. After oviposit- 

 ing, however, the adults may live on and injure the foliage of the plants 

 for more than a week. 



