Dec. is, 1920 Opiu9 fletcheri, Parasite of the Melon Fly in Hawaii 427 



body is very delicate and can be easily crushed beyond recognition with 

 a very slight pressure on the coverglass. The digestive tract is simple 

 and tubular and is closed caudally as in the first instar. In this stage the 

 larva is sluggish in its movements, although it rapidly ingests a quantity 

 of fat into its mid-intestine. Toward the latter part of this instar the 

 mandibles of the third 

 instar can be seen 

 pushing at the bases 



Fig. 5. — Optus fletcheri: New second-instar larva. C.reatly enlarged. 



Fig. 6.— Optus fletch- 

 eri: Mandible of 

 second-instar larva. 

 Length 0.045 mm. 



of the mandibles. 



The third instar, 

 when first formed, is 

 without a vestige of 

 tracheae. Tracheae 

 can be seen developing beneath the surface of the integument toward 

 the latter part of this stage, but they are of the last instar and 

 serve no purpose in the third. Few differences can be detected between 

 this and the preceding instar, except an increase in size and a change in 

 the shape of the mandibles. The third-instar larva measures 2.5 to 3 

 mm. in length. The mandibles (fig. 7) are somewhat more pointed and 

 strong than those of the second instar; they bear no 

 colored chitinization and measure 0.047 mm - i n length. 

 Toward the latter part of this instar the strong, chitin- 

 ized mandibles of the last instar can be seen pushing 

 at the bases of the mandibles. 



The mature, fourth-instar larva (fig. 8) averages 4 

 mm. in length and at its greatest width is about three- 

 eighths as wide as long. When first molted into this instar it is 3 to 3.5 

 mm. long. The body is slightly curved, being concave ventrally, and, 

 including the head, is composed of apparently 14 segments, although 

 segment 14 is not clearly defined. A rather large, distinct spiracle is 

 present on each side of segments 3, 5, 6, 7, 8, 9, 10, 11, and 12, counting 

 the head as segment No. 1. These spiracles are joined 

 on each side by a large lateral trunk extending nearly 

 the length of the body. The trunks are connected near 

 their caudal and cephalic extremities by a single, trans- 

 verse, connecting trunk, these being the only connections 

 between the two lateral systems. Branches from the lat- 

 eral trunks extend dorsally and ventrally into each body 

 segment, and prolongations of the lateral trunks extend 

 into the head region. Portions of the body are covered by minute, strong, 

 wide-based spines (fig. 9), which are closely set and abundant on the dorsal 

 and lateral portions of body segments 2 and 3, counting the head as seg- 

 ment No. 1, and on the lateral areas of segments 4 to 12, inclusive. No 

 spines occur on the head, on the articulation areas between the segments, 

 or on the ventral portion of any segment of the body, and very few occur 



Fig. 7. — O pius fletch- 

 eri: Mandible of 

 third-instar larva. 

 Length 0.04 ymm. 



