229 



single individual will secrete during its lifetime is small, but when many thousands of 

 the insects occur on a tree the aggregate becomes large. A single nymph isolated in 

 a cage secreted at least four drops (i. c. four minims) of the fluid before it became an 

 adult. Thus fifteen nymphs would secrete one draclim. 



The food of tln^ insect consists entirely of the sap of the tree. * * * In the 

 case of the nymphs most of the food is elaborated into honey-dew ; some is assimi- 

 lated, and the waste matter voided as excrement. The adults, however, seem to 

 secrete no honey-dew, all the food being assimilated. Consequently the adults void 

 considerable quantities of excrement, much more than do th<^ nymphs. 



The honey-dew and excrement are very different substances, but the fact does not 

 seem to have been before observed. The honey-dew is a clear, water-like li(iuid and 

 forms into globules when secreted. The excrement, however, is a whitish semi- 

 solid substance which is voided in long cylindrical strings or minute whitish balls 

 which roll from the anus like quicksilver globules. * * * Many observations 

 were made to discover, if possible, the manner in which the honey-dew was secreted 

 by the nymphs. It has been supposed that the secretion came either from the long 

 so-called wax-hairs around the edge of the abdomen, or from excretory pores on the 

 dorsum of the abdomen. Globules of honey-dew were, however, seen attached to 

 the nymphs in such a position that it seemed very improbable that it came from either 

 of the above sources ; it seemed that it must have been secreted from the anus of 

 the nymph. A German observer now asserts that the honey-dew secreted by the 

 common plant-lice or Aphids comes from the anus, and not from the honey -tubes as 

 commonly supposed.* Honey-dew thus seems to be what might rightly be called 

 the fluid excrement of the insect. 



A full account is given of an extensive series of experiments to ascer- 

 tain tlie best remedy. All experiments upon the eggs failed but the 

 young nymphs were shown to be very susceptible to the action of kero- 

 sene. The standard emulsion, even when diluted with 25 parts of wa- 

 ter and thus containing less than 3 per cent of kerosene, was very effica- 

 cious. From 75 to 90 per cent were killed with one spraying in this 

 proportion. The nymphs have a habit of clustering in the leaf axils 

 and as the liquid naturally runs down the leaf jjetioles and twigs the 

 insects are readily reached. Two quarts of the dilution were sufficient 

 for a large dwarf pear tree and thirteen such trees can easily be sprayed 

 in half an hour with a knapsack sprayer. The best time to spray is 

 said to be in the early spring just after the leaves have exj^anded. 



Yery full technical descriptions are given of the full-grown nymph 

 and the summer and winter forms of the adults. 



In the description of the imago Mr. Slingerland introduces for the vari- 

 ous parts of the body a terminology which differs from any other in use 

 for this family. In fact, in the Psyllidse we have almost as many differ- 

 ent terminologies as there are authors. This by no means facilitates the 

 study of these insects, and there is no good reason for the term "cly- 

 peus" or " cones of the clypeus " (see Fig. 28, c) for that part of the head 

 which, following Low, we have called '^ frontal cones" (Scott's '^face 

 lobes"). In Psyllidse the clypeus is to be looked for on the underside 

 of the head where it is visible as a more or less knob-shaped (very rarely 

 more elongate) protuberance a little in front of the anterior coxae. The 



* M. Busgen, Jenaische Zeitschrift, vol. xxv, pp. 339-428 (1891). 



