Fig. 173 



Diagram illustrating life cycle of Scatotienui iriilkeri. The adult para- 

 sitic female (a) produces offspring (b) that eventually enter the female 

 fly s reproductive organs and are extruded with the eggs (c). Outside 

 the host these larvae develop into adults (rf) and copulate whereupon 

 males die and impregnated females (e) enter flv larvae. These females 

 then undergo a period of growth (/) and mav begin producing off- 

 spring (n«) while the fly is still in the larval stage or females mav be 

 only partly grown (though adult) (p) when the flv pupates and begin 

 flaying eggs (a) when the fly becomes adult. After Bovien, 1937. 



Fig. 174. CnONDROXEMA PASSALI 



A — Oldest larva found within body cavity of host: B — Youngest larva 

 found within body cavity of host: C-E — Portions of body of adult fe- 

 male filled with eggs or larvae and serving as brood sac; P — Eggs. 

 All figures after Christie and Chitwood. 1931. 



nal [esophageal] gland, nliieli prevents tlie normal growth of 

 the host's sex-eells. At the same time it. is quite likel.v that the 

 same may be true of the host; if once its reproductive organs 

 become sufficiently developed, then it is able to pour out some 

 substance which definitely inhibits the growth of the worm." 

 Allantonema mirable Leuckart, 1884, is a bodv cavitv 

 parasite of the pine weevil, Eylohius ahirtis (L.) and occurs 

 in Europe but has not been found elsewhere. This nematode 

 differs from TylencMnema oscinellae, not so much in its life 

 cycle, which is essentially the same, as in the form and degen- 

 eration of the gravid female. Unlike most allantoiiematids, the 

 fully grown female (Fig. 171 J) is oval, some L.T to 2 mm. 

 in length and about half as wide as long. Its bodv is virtually 

 a sac largely filled by the uterus as it becomes di.stended witii 

 eggs and larvae. The other internal organs degenerate to such 

 an extent that if vestiges persist their identitv has not liecn 

 recognized. 



Eggs hatch in the uterus where they begin to accumulate 

 during late summer and where they remain during the winter 

 undergoing little development. In "the spring larvae begin to 

 pass through the vulva into the body cavity of the weevil 

 where they undergo two molts. Larvae finally leave the host by 

 penetrating its alimentary tract and passing out thiougli tlie 

 anus. 



The adult female of Hylnbins abiFfix eats small holes in the 

 bark on the trunk and roots of fir and certain other coniferous 

 trees. In this cavity eggs are laid and hatch, the young weevils 

 tuiineling into adjacent tissues. In order to pass their free- 

 living stages in the immediate vicinity of newly hatched weevils, 

 the larval nematodes must escape when and where female 

 weevils are laying eggs, albeit not through the genital aperture 

 of the insect. Wiilker (1923) observed only one molt during 

 free-living development which took place after 8 to 10 days. 

 Bovien (1937) found that larvae, taken from the rectum of 

 adult weevils and placed in hanging drops of water, became 



adult in 5 to 6 da3'S. The final molt is followed very soon by 

 copulation after which males die and impregnated females enter 

 the body cavity of weevil larvae that, in the meantime, have 

 hatched. 



The adult preparasitic female of A. mirable (Fig. 171 I) has 

 a well developed stylet and Bovien (1937) figures two esopha- 

 geal glands, one opening into the esophagus on the dorsal side 

 near the base of the stylet and the other on the ventral side 

 farther back. In the adult male (Fig. 171 H) a stylet is pres- 

 ent though somewhat more weakly developed than in the female 

 but the esophageal glands are inconspicuous or lacking. 



By about July, when the weevils are pupating, the parasitic 

 female nematode is producing ova. Fuchs (1915) states that 

 ni/lohiiif: abii'tis lives for at least 31 months and, finding fe- 

 males of A. mirable in 2-yearold weevils, he concludes that the 

 nematode lives for at least 2 years. 



SrATOXEM.4. wuLKERi Bovien, 1932, is a liody cavity parasite 

 of the dipterous insect, Scatopse fiiscipes Meig., the immature 

 stages of which develop in manure and other putrescent mate- 

 rial. Eggs of this nematode hatch in the uterus where larvae 

 (Fig. 172 A & B) undergo early development, the extent of 

 this development varying considerably. In some cases, which 

 Bovien (1932) regards as exceptional, an individual, while still 

 within the uterus, ma.y reach maturity and, in turn, develop 

 larvae within its uterus, thus creating three generations, one 

 within another. Most of the progeny, however, pass through 

 the vulva into the body cavity of the host as partly grown 

 larvae. These larvae enter the reproductive system of the in- 

 sect and pass out with the eggs. When an infected fly dies 

 not all the harbored parasites necessarily perish but some 

 larvae may complete development, molt, and copulate after 

 which impregnated females escape from the dead body. As 

 male flies die soon after copulation Bovien concludes that, in 

 moist surroundings, part of the nematodes may be able to 



260 



