INSECTS TETTIGONID.* (continued) Evacanthus interruptus, L. Tcttigonia, Geoff. viridus, L. ACOCEPHALIDVK Acocephalus, Germ. nervosus, Schr. albifrons, L. Eupelix, Germ. cuspidata, Fabr. JASSID/E Allygus, Fieb. commutatus, Fieb. modestus, Fieb. - mixtus, Fab. Thamnotettix, Zett. dilutior, Kbm. subfuscula, Fall. (continued) Thamnotettix crocea, H.S. TYPHLOCYBID.W Alebra, Fieb. - albostriella, Fall. Chlorita, Fieb. flavescens, Fabr. Eupteryx, Curt. vittatus, L. urticze, Fabr. - pulchellus, Fall. PSYLLINA PSYLLID.* Psylla, F. Low alni, L. Arytaena, Scott genistz, Latr. APHIDES Plant Lice Although dwellers in the country are necessarily much too familiar with the insects included in this section, nobody seems to have system- atically studied and differentiated the Essex species. Of all insects they are the most numerous, the most ubiquitous and the most harmful, and the loss they sometimes occasion is incalculable. They infest alike the lowliest herbage and the loftiest trees ; some live underground upon roots, out of which they suck the sap, and others submerged in water upon aquatic plants. In former times it was imagined that every plant had its own peculiar Aphis, and as the various species were named after the plants upon which they were found some of them received a large number of names, which are sunk as synonyms now that we know that the same Aphis in some cases affects a great many different plants, and that some of these afford sustenance to several different Aphides. When they first appear in the spring they are not very numerous, but they arrive at maturity so rapidly, and increase at such a prodigious rate, that before the summer is far advanced it is said a single individual may number its descendants by hundreds of millions, and the term ' Smother-flies,' which is sometimes applied to them, is then amply justified. Their life history is very interesting and peculiar, for the ordinary processes of nature have been so materially modified to meet their special case that the actual facts would appear almost incredible if they had not been abundantly proved. The first brood of the year emerges from eggs which have been laid by the fertilized females of the previous autumn, and consists of females exclusively, which without any male intervention bring forth other females, and the process is con- tinued as long as a suitable food supply lasts and the climatic conditions remain favourable ; but when these change a bisexual brood is produced, the males of which fertilize the females, and eggs are deposited which 191
