PearthripS 



M Continued from front cover ^^-^ 



Pear thrips were introduced to 

 early 1900's and were first 

 pear and other pome trees in 

 passing of many years and the 

 controls, this pest became less 

 However, at the same time, 

 throughout most of the 

 and acquiring a wide range 

 oak, beech, lilac, walnut. 



the USA from Europe in the 

 observed as a major pest of 

 California. With the 

 development of effective 

 of a problem in the West, 

 pear thrips were spreading 

 northern United States 

 of new hosts including 

 laurel, dogwood, and sugar 



maple. In 1978 a few sightings of moderate damage in sugar maple were 



reported in Pennsylvania, with pear thrips identified as the cause. 



Then the thrips outbreak occurred in New England. 



THRIPS 



Thysanoptera, or thrips, are bizarre 

 insects. Even the name "thrips" is 

 unique, ending with as "s" and 

 having the same spelling in its 

 singular and plural form. (Hence, 

 there is no such thing as "a thrip.") 

 It was not until recently that 

 scientists observed how thrips feed 

 on plants. An herbivorous thrips 

 feeds by attacking individual plant 

 cells. First it punches its mandible 

 into the cell wall, making a minute 

 hole; then it inserts a siphoning- 

 tube into the hole and sucks out 

 the cell's liquid contents. The legs 

 of thrips are quite unique, being 

 specialized for digging through the 

 soil, and walking on rough surfaces, 

 like tree bark, and very smooth 

 surfaces, like leaves. The average 

 thrips (1 to 2 mm long) is so small 

 that you might not even notice one 

 if it landed on your nose. Thrips 

 have wings that resemble small 



feathers, and in flight they almost 

 float through the air like dandelion 

 seeds. Because of their method of 

 flight and their minute size, thrips 

 are well adapted for dispersion by 

 the wind. 



PEAR THRIPS 

 Pear thrips in North America 

 reproduce by parthenogenesis, i.e. 

 females reproduce without 

 fertilization (males have only been 

 observed in native European 

 populations). Each female can 

 produce 100 to 200 eggs; widi her 

 saber-like ovipositor she inserts 

 each egg into the tender petiole or 

 midvein of a young leaf. The 

 oviposition site later swells and 

 each egg hatches within 7 to 10 

 days. In New Hampshire, young 

 thrips are common in June and feed 

 on die under surfaces of leaves. By 

 July most of the young have 

 dropped to the ground and 



penetrated into the soil to depths 

 usually ranging from 1 to 26 inches. 

 Underground, they hollow out 

 small ovoid chambers and develop 

 into adults. Shortly after the 

 ground thaws in late March, the 

 trips emerge and begin to search for 

 food. Adult pear thrips are 1 .3 mm 

 long and dark, almost black, in 

 color. 



DAMAGE 



Pear thrips attack sugar maple 

 immediately after bud-break (about 

 the time when syrup makers stop 

 collecting sap). The adults dig into 

 the buds to feed. This often kills 

 the bud, resulting in defoliation, or 

 it causes severe leaf disfiguration. 

 Bud damage will also destroy 

 flowers, thus affecting seed 

 production. When adult and young 

 thrips feed on immature leaves, 

 they cause leaf mottling, and the 

 egg-laying of females produces 



April/May 1992 13 



