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Fig. 173. TTLEXCHINEilA OSCINELLAE 



Schematic drawing illustrating life history of frit-fl.v in its three 

 ^easonal generations, and the approximate time occupied by each, linked 

 with that of its parasite. Tylenchinema oscin^llae. The various stages 

 of the rty and worm are greatly enlarged whilst the outs and gr.Tss are 

 smaller than natural size. Although the female fly only is shown it is 

 to be understood that the male also carries the parasite. The dotted 

 circles contain stages of the parasite related to the corresponding stage 

 of the host. The circles cut into the pupa and imago hut not into the 

 fly larva in each case, thus showing that the parasite is within the pupa 

 and fly hut not within the larvae, c I, ensheathed larvae; / r, food 

 reservoir of fly with larvae passing in: g f, growing female worms; 7» /. 

 mature female worms, .^fter Goodey, 1931. explanation quoted verbatim. 



escape from the decaying insects. Otherwise tlie fate of larvae 

 harbored by male fiies is unknown. 



Bovien observed only one molt, the last, which may occur 

 liefore, but usually not until after, emergence from the host. 

 As this molt takes place not later than 24 hours after emer- 

 gence and is followed immediately b.v copulation, the free living 

 stage is of short duration. In the adult, preparasitic female 

 (Fig. 172 F) the stylet and esophageal glands (Bovien figures 

 two) are well developed while in the adult male (Fig, 172 G) 

 these structures arc inconspicuous or absent. By the less well- 

 developed genital primordium and the presence of esophageal 

 glands one can distinguish female larvae while they are still 

 within the egg. 



Regarding penetration of preparasitic females into the body 

 cavity of a fly larva Bovien (1932) writes as follows: "In 

 many cases I found the nematodes in the act of entering the 

 body of the larva. In a few cases I saw dead nematodes, which 

 had not succeeded in penetrating the body wall, held fast by it. 

 Tlie jienetration may take place through all parts of the surface 

 of the larva and no preference seems to be given to any ])ar 

 ticular region. The very beginning of this act, however, was 

 not observed. I placed female worms in hanging drops 

 together with Scatopse-\aT\ae, the presence of which had an 

 unmistakably attractive influence on the nemas. The 

 nematodes slung themselves around the body of the larva, 

 pressing their mouths against the skin without being able to 

 puncture it, I suppose this failure may be :iscril)ed to the lack 

 of supporting surfaces. On the third day the worms were dead. 

 ,\n oblong, somewhat spiral-wound, coagulated ma.ss of secre- 

 tion had been ejected from the aperture of the buccal stylet, 

 and the salivary [esophageal] glands apjieared to be empty.'' 

 The jjrcscnce of the parasite does not result in sterility of thi' 

 host. 



Chondronema PASSALi (Lcidy, 18.')2) Christie and Chitwood, 

 Ifl.Sl, is a body cavity parasite of the beetle PopiliiiK ivlrrr\ip- 



Fig. 176. HETEROTYLENCHUS ABERRANS 



Diagram illustrating life cycle of Heterotylenchua aberran.t. The 

 adult parasitic female of the gamogenetic generation («) lays eggs (6) 

 that develop into females of the parthenogenetic generation (c). These 

 females lay eggs (rf) and the resulting larvae (e) enter the reproductive 

 organs of the female fly and pass out through the genital aperture. 

 Outside the host these larvae develop into adults of the gamogenetic 

 generation (/) and copulate whereupon males die and impregnated fe- 

 males (ff) enter fly larvae. While the fly matures and pupates the fe- 

 male grows (/i) to reach full stature (a) and lav eggs (b) . After Bo- 

 vien. 1937. 



tits (L.) (Syn. Pasxalus cnrnutns Fab.). This beetle occupies 

 galleries in decaying stumps and logs where eggs are laid and 

 where larvae develop and pupate. Leidy (18.52) found 90 per- 

 cent of the adult beetles infected and Christie and Chitwood 

 (1931) estimated that each beetle usually harbors from .")00 

 to 1,000 parasites. In the body cavity of the insect one finds 

 larvae in all stages of development from young, newly hatched 

 individuals (Fig. 174 B) to those that are fully grown (Fig. 

 174 A) but never adults. 



Larval nematodes of both sexes taken from the body cavity 

 of a beetle have a minute stylet, a moderately large esophageal 

 gland (presumably the dorsal), and exceptionally large and 

 conspicuous phasmids. Sex can be distinguished at a rather 

 early stage partl.y through differences in the genital primordia 

 but more especially through differences in the general appear- 

 ance of the body, females being more opaque than males. Move- 

 ment is sluggish. 



The mode of exit from the host has not been determined. 

 Once the nematodes have escaped neither males nor females 

 again become parasitic but remain in the beetle galleries 

 throughout the remainder of their lives. The mouth, anus, and 

 vulva of the female become vestigeal. If the vulva functions 

 it is only during copulation. Eggs (Fig. 174 F) are retained 

 within the body where they accumulate and hatch pushing aside 

 the internal organs and converting the female into a brood 

 sac (Fig. 174 C-E). 



C. passali enters its host as a very young larva but it is not 

 known how this is accomplished. Larvae of all sizes may be 

 found in old beetles at any time of the year when the insects 

 can be collected. The incidence of infection seems to be very 

 much lower in larval beetles and pupae than in adults. These 

 circumstances, together with the exceedingly large number of 

 parasites usually harbored by a beetle, caused Christie and 

 Chitwood (1931) to suggest that the larval nematodes enter 

 per 0.1, possibly the gravid female and her entire progeny being 

 swallowed. 



261 



