1 82 



THE APPLE LEAF HOPPER 



spur these ridges become ver}- prominent and run nearly around or 

 around the joint. 



The Rostrum: The clypeus, labrum. mandibular laminae, and 

 first maxillary laminae form a raised tubercle on the ventral side of 

 the head, which may be appropriately called the trophic tubercle. The 

 clypeus is in one piece, nearly oval in outline as you look down upon 

 it from the ventral side. The labrum joins the distal end of the 

 clypeus. It is composed of a rectangular basal part which suddenly 

 narrows at its distal end into a long pointed triangular distal part 

 covering a groove in the labium. The mandibular lamina lies partly 

 under the clypeus and the labrum ; the exposed portion having the 

 shape of a segment of a circle. The first maxillary lamina lies under 

 the mandibular lamina, and the labrum, usually only a small por- 

 tion of it is exposed, but this varies in the different species. The 

 labium is lengthened into a long rostrum. This is seen in its most 

 primitive or generalized condition in Lachnus, where (L. laricis) it is 

 five-jointed. The first two joints are grooved on their anterior faces; 

 the third perforated ; the fourth and fifth are grooved. The suture 



between the second and third joints is 

 diagonal. There has been some question 

 as to whether the rostrum is three or 

 four jointed. This difference of opinion 

 has arisen because of the obscurity of 

 the suture between the first and second 

 joint. By careful examination this su- 

 ture can be observed and the four joints 

 made out. But in the most primitive 

 genus, Lachnus, the fourth or terminal 

 joint is in some species divided by a very 

 distinct suture and a fifth joint is pres- 

 ent. This is probably the primitive con- 

 dition. The rostrum varies greatly in 

 lengtli in the different genera. In some 

 it reaches hardly beyond the first coxae 

 while in others, as some Lacltinn?^, it is 

 much longer than the body. There is 

 some dift'erence in the relative lengths 

 of the joints which might be used as a 

 specific character. In Lachnus and Me- 



Fig. 95. The mouth parts of Aphi- 

 dldae: A, Rostrimi of Lachnus 

 laricis. B, Trophic tuberck- of 

 Macrosiphum: a.Olypeus; b, lab- 

 rum: c, mandilnUa^- ^^lamina;^ d. /^,„^ ^.^„//,j/^^ the trophic tubercle is VCr} 



hairw In the other genera there are 



maxillary lamina; 

 the labrum or rostrum. 



typically two pairs of hairs on the clypeus, a row of three hairs on each 



