166 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



Order Thysanoptera. The curious little insects known as 

 thrips, or fringe-wings, which used to be classified with the 

 Hemiptera, are now given the standing of an independent 

 small order. This is due to the peculiar character of their 

 mouth-parts and feet, and to the interesting nature of their 

 development, which is apparently of a sort of transitional con- 

 dition between incomplete and complete metamorphosis. The 

 food of the thrips is either the sap of living plants or moist 

 decaying vegetable matter, especialy wood and fungi. The 

 mouth is of sucking type with needle-like mandibles and 

 maxillae to pierce plant tissue, but it is curiously asymmetrical, 

 the right mandible being wholly wanting and the upper lip 

 being more expanded on one side than the other. The feet 

 have a small protrusible membranous sac or bladder at the 

 tips instead of fixed claws or pad. These tiny sacs probably 

 fill some special role in enabling the thrips to hold on to leaves 

 or flower surfaces. 



While most of the thrips species live on wild plants, a few 

 infest fruits, grains and vegetables, and do much injury. 

 Among these are the onion thrips, wheat thrips, grass thrips, 

 orange thrips and pear thrips. This last pest appeared 

 suddenly in California a few years ago, and since then has 

 caused the loss of millions of dollars worth of prunes, apricots 

 and other deciduous fruits. Several of the thrips are described 

 in the later special chapters on injurious insects. 



Order Neuroptera. The Neuroptera, constituting a small 

 order in point of numbers, are insects with biting mouth-parts, 

 and a metamorphosis usually called complete, but in which the 

 larval stage resembles somewhat the adult stage, and the pupal 

 stage is not usually undergone as a wholly immobile chrysalid, 

 but more often in a condition which suggests that of an inac- 

 tive larva with conspicuous external wing-pads. This stage 

 is usualy passed in a special cell or cocoon made by the larva 

 when full grown. The adults have four membranous, many- 

 veined or so-called "nerve-veined" wings, hence the name of 

 the order (neuron, nerve, ptera, wings). The Neuroptera 

 include seven families of mostly unfamiliar insects, some very 

 large, and others extremely small. The immature stages of 



