318 



REPORT OP STATE BOARD OF HORTICULTURE. 



Fij: 



. ?. — Apple plant louse, just 

 from egg; antenna and honey 

 tube more enlarged. 



considered as coincident with the opening of 

 the apple-leaf buds. 



On the experiment tree the buds began to 

 start April 15, and on that day I found two 

 plant lice, just from the egg, feeding on a bud 

 that had scarcely more than broken the scaly 

 covering ; in other words, before there was 

 even a sign of foliage. On the sixteenth 

 many more specimens were seen, and on the 

 seventeenth almost every bud had from two 

 to ten ])lant lice sucking its juices. To get a 

 definite basis for my record as to length of 

 time required for the development of this series, I cleaned the insects from 

 every bud on the eighteenth, brushing them up with a hair pencil into an 

 alcohol vial. 



April 20 there were no lice over two days old on the tree, and the opening 

 buds on some of the twigs were again completely covered. A few cast skins 

 were seen, indicating that some specimens had already molted once. The 

 larva just from the egg is an awkward creature, with rather long, fleshy 

 legs, that seem to be in its way rather than helpful, and short, stout antennae 

 or feelers. These feelers are made up of four joints: Two short and thick 

 at the base; the third more slender, almost twice as long as the others 

 combined: the fourth tapering to tip, shorter than the third, and with a 

 sensory pit at the thickest portion. 



The sensory or sense pits on the antenna; of plant lice, to which frequent 



reference will be made in this account, are 



\^ a organs whose use"is yet obscure to us. Judg- 



.^^^^YTTf'^^^r^^'^^^ I ^"» ^y their structure they should serve as 



ears or organs j of hearing, but this is by no 

 means certain. 



The honey tubes are very small, little 

 more than mere warts or tubercles, with 

 round openings at the tips. This combina- 

 tion of a small honey tube and a feeler in 

 which there is a single sensory pit on the ter- 

 minal joint, is peculiar to this larva just from 



Fifj.^ Second .stage of the larva; ^j^ q ^f ^he later broods have it. 



antenna and honey tube more o*' ' 



enlarged. Two or three days after emerging from the 



egg the larva outgrows its skin and molts. It now appears in a new dress, 

 almost one-half longer than it was before and considerably stouter. The 

 legs seem to be proportionately shorter and less clumsy : but the insect is 

 quite as little inclined to move about as it was before. The honey tubes are 

 now much larger and quite obvious. They are as 

 long as one segment of the abdomen, quite stout, 

 and tapering a little to a i^ounded tip. 



These honey tubes are peculiar structures, found 

 only in the plant lice, and they serve a unique pur- 

 pose in the history of some species. It is a common 

 observation that wherever plant lice are abundant 

 ants are likely to be found, and it is a usual con- 

 clusion that the ants feed upon the jilant lice. As 

 a matter of fact this is not so ; the ants and the 

 aphids are on the best of terms, and in many in- 

 stances are useful to each other. ' ' The ants in such 



cases obtain from the plant lice\iroplets of honey Fig. 5— Second stage from 



J . above ; enlarged. 



