Aug list 



September 



Octtbrr 



huv. -Alir 



Hay 



Ju n e 



July 



Fig. 170b. I.IKK rYCl.E OF AGAilKltMlS DECAVDiTi — Continued 



Disgram ilhislraling fnsuiiig rj-nionth piTioii. August to July, in- 

 clusive, c, nierniilhids einerKtiig from hosts SejiteinlxT to October. Fe- 

 nmle and miiies remain in separnte cavities until latter iiart of May 

 when males seek female, copulation takes place, and. ilurins; .luiie, the 

 (emnle begins it-s first summer of egg laying. Female in "knot" h has. 

 by October, completed its second summer of egg laying and dies during 

 the ensuing winter but the accumulated eggs hatch May to .June. (While 

 the above diagram is essentially correct for a nia.iority of individuals 

 where grasshoppers serve as hosts, the various life-cycle changes are 

 actually spread out over somewhat greater periods of time than the 

 diagram indicates. A few eggs hatch before May and June. A few 

 prcparasitic larvae enter hosts as early as .\pril and as late a.s August 

 and the time of emergence is correspondingly affected. A few individuals. 

 especially males, emerge from hosts at least as early as July.) 



leave the host is via the female reprtiduetive system ami the 

 fate of Uirvae that iiilialiit the beily cavity of male insects is 

 not yet fully understood. 



A free living stiige is passed wheievor the liost in.scct umlef- 

 goes its early development and during tliis period the nema- 

 todes molt at least once (as a rule prohalily twice) and Ijccome 

 adults. In the adult male the stylet is usually either ahseiit or 

 weakly developed and the esophageal glands are ineonspicuous 

 ami apparently lacking. In the preparasitie adult female the 

 stylet is usually well developed and at least one of the esopha- 

 geal glands is large and conspicuous. E.xeeptions to these mor- 

 phological differences between the sexe.s are usually correlated 

 with deviations from the more typical life cycle. The apparent 

 absence of esophageal glands and the somewhat more rapid de- 

 velopment of the genital primordiuni in the male usually make 

 it possible to distinguish sex at an early stage sometimes while 

 a larva is still within the egg. 



The ovary of the adult preparasitie female is small and com- 

 posed of only a few cells the extent of its development differ- 

 ing somewhat with different species. When copulation takes 

 place the uterus is packed with small, more or less spherical 

 spermatozoa. After copulation males usually die and impreg- 

 nated females enter their respective hosts, usually by penetrat- 

 ing the body wall while the insect is still in the larval stage. 

 The fact that in most species only the female possesses an effec- 

 tive stylet and at least one well-developed esophageal gland has 

 been regarded as evidence that these structures function in 

 connection with penetration into the host. There is little reason 

 to doubt that the stylet is employed for this purpose. It has 

 been suggested that penetration is further facilitated by a 

 secretion of the esojihageal glands which may serve as a cliitin 

 solvent. The validity of this suggestion does not rest entirely 

 on morphological evidence for Bovien (1S)32) demonstrated that 

 ScntDtirma wiill'cri does, in fact, exude a rather copious secre- 

 tion through the stylet at the time of penetration. 



The free-living stage is usually of short duration. There is 

 no evidence that the nematodes feed during this period (with 

 the exception of Fergusobia citrrici) and larvae, at the time 

 they leave the host, are at least nearly as large as young 

 adults. However, after entering a new host, the female under- 

 goes a very great increase in size. The fully grown gravid fe- 

 male of most species is curved ventrad ;ind assumes a form 

 usually referred to as "sausage-shaped." There are exceptions, 

 however, and, for example, AUantonrma miriiblr is oval while 

 in many species of A ph clench id us the body is bent dorsad with 

 the vulva on the outside of the curve. 



Some species deposit eggs in the body cavity of the host but 

 in many species eggs hatch before deposition and the uterus be 

 comes distended with developing eggs and larvae that gradually 

 fill the greater part of the body and push the ovary into the 

 anterior end. As a rule larvae eventually pass through the 

 vulva into the body cavity of the host. There is a tendency for 

 the other internal organs of the female to degenerate, the ex- 

 tent of this degeneration differing in different species. 



In most species the rapid increase in the size of the female 

 after becoming parasitic provides space for the rei)roductive or- 

 gans. In one group, the Sphaerulariinae, adequate s|iace for the 

 developing reproductive organs is not provided by a corre- 



sponding increase in body size. The uterus of Si>li(ini(laria 

 hombi is everted through the vulva and the entire reproductive 

 system develops outside the body jiroper. This prolapsed uterus 

 increases enormously in size and the body proper remains at- 

 tached to otu^ end :is a vestigial and apparently fiinctionless 

 structure. 'I'ripiu.i i/ibbusut! (Syn. Alractoncma iiibbumim) rep- 

 resents an intermediate stage in the evolutionary developnuMit 

 of this peculiar adaptation and the size of the body and of the 

 jMolapsed uterus is le.ss disproportionate. In both these species 

 the life c.vele, so far as known, is essentially the same as that 

 of most allantonematids. 



There are, nevertheless, several deviations from this typical 

 life cycle. Young adult males, as well as young adult females, 

 of Par(i.iiti/lciicliii.s di.ipar typograpki enter the body cavity of 

 their host insect where they are found in large numbers, while 

 neither adult males nor adult females of Chondronema passali 

 become parasitic, only larval stages being found in the host 

 insect. Chnndronevia pansali enters its host, not as young 

 adults, but as young larvae, probably by being ingested. 



Two species of this family have heterogeneous life cycles. 

 There is interpolated into the life cycle of Heteroli/lcncliiis aber- 

 rans a parasitic, parthenogenetic generation and into the life 

 cycle of Fergusobia ciirriei several, consecutive, "free-living," 

 parthenogenetic generations. The parthenogenetic females of 

 Fergusobia currici occur, associated with their "host" insect, in 

 plant galls where they feed on plant cells and are, in fact, 

 plant parasites. In each of these heterogeneous species, how- 

 ever, the gamogenetic generation still follows the typical allan- 

 tonematid plan of development. 



Tylenchinbma oscinellab Goodey, 1030, is a body-cavity 

 parasite of the frit-fly, Oscinclla frit. (L.). The life history of 

 this nematode was studied in England by Goodey (1930, 1931). 



The frit-fly has three generations a year. Eggs are laid on 

 small oat plants generally during May and fly larvae penetrate 

 the shoots, destroying the central tissues. This is the first or 

 stem generation. Adult flies appear by mid-July and deposit 

 eggs on the panicles of oats where the larvae attack the tissues 

 of the inflorescence. This is the second or panicle generation. 

 Adult flies again appear during August or early September and 

 lay eggs on various species of wild grasses. This is the third 

 or grass generation; also it is the overwintering generation and 

 winter is passed in the larval stage. The life cycle of the nema- 

 tode is, of necessity, closely correlated with that of the frit- 

 fly and like it, undergoes three generations a year (Fig. 17.5). 



Infected flies hariior usually one, sometimes two or three, 

 more rarely four to eight, adult female nematodes that give 

 birth to living young. Eggs pass into the uterus of the mother 

 nematode where they undergo development. As more and more 

 eggs are produced the uterus becomes distended, pushing the 

 ovary into the anterior end and finally occupying most of the 

 space within the body. Larvae (Fig. 171 A & C), escaping 

 from the egg membranes, pack the posterior etui of the uterus 

 and finally pass through the vulva into the body cavity of the 

 host. Here they accumulate and continue development. Goodey 

 observed one molt that takes place when a larva is about 4G0/i 

 long and which he believed to be the second suspecting that the 

 first molt takes place while the larva is still within the uterus of 

 the mother. The gonads undergo considerable development and 

 show differences that make it possible to distinguish sex. The 

 wall of the intestine becomes well stocked with reserve food 

 globules. 



After attaining a size nearly as large as free-living adults, 

 the larvae escape from the host. To accomplish this they pene- 

 trate the food reservoir of the fly's digestive system from which 

 they migrate through the intestine to the rectum and are e.iected 

 through the anus. With regard to this escape of larvae, Goodey 

 writes as follows: "Parasitized flies of both sexes, having 

 failed to develop their sex cells, fly about and instead of taking 

 part in the normal process of reproduction are able only to 

 deposit larvae of the nematode parasite. Normal females go to 

 oat panicles and there lay eggs; similarly, the parasitized fliea 

 responding to the same urge of the life-cycle rhythm also fly 



2o7 



