iiiiclmiiKcd, :i|>))aii'iitly liaviiiK iio adverse effeot on the inswt. 

 WIu'ii rvt'iitnally the insect dies, presunmlily from otlier causes, 

 the larvae move into its tissues and jiroceed in development, 

 IiassiuK tlmiUKli several penerations and <|nickly IniildiiiK uji a 

 large iiopulation. When the carcass has lieeii consumed youug 

 nematodes move out into the soil and develop into dauer larvae. 



Although Hies become infected while in the larval stage, if 

 the nenuitodes, on reaching the intestine, are wholly innocuous, 

 many of the insects must carry their infection on into the adult 

 stage. Rovien is not very lucid on this jioint Init he merifioTis 

 finding nematodes in living 1]\ i)upae, on one occasion in tlu' 

 tiody cavity. 



Bovien concluded that development from egg to egg laying 

 female requires about 4 days. A young female is oviparous but 

 some of the last eggs laid by an old fcm.'ile liatch within the 

 uterus. Kach female usually produces somewhat in excess of 

 -"" eKRS. 



It is not strictly necessary that N. bibioni.i enter living in- 

 sects as Rovien was able to rear several generations on dead 

 insects of different sjiecies if fresh cadavers were periodically 

 provided. Several generations could sometimes be reared on 

 egg albumen. 



Gravid fenuiles (Fig. IG.') E") usually attain a length of up 

 to ■> mm. but Rovien reports finding mature, rci)roducing fe- 

 males that failed to reach a length of 1 mm. (Fig. IG.l H), per- 

 haps due to some nutritional deficiency. Between these dwarfs 

 and females of maximum stature numerous intermediate sizes 

 were found. 



NEO.\PI,E(.-r.\NA GLASERI Steiner, lili!!1, was first fovind in dead 

 larvae of the .Japanese beetle, ropillid japonica Newni., col- 

 lected in New Jersey and is best known as a jiarasite of this 

 insect. However it has been demonstrated that this nematode 

 will infect larvae of the Enrojiean corn borer, Purausta nu- 

 bilalis (Hiibn.) and coleopterous larvae belonging to at least 

 nine genera including the white fringed beetle, Pnntomorus tcu- 

 colnma (Boh.). 



The life historv of .V. glascri has been investigated by Glaser 

 (1932) and by Glaser, McCoy and Girth (l',t40). The following 

 account is based on their results that were secured, in part by 

 using Japanese beetle larvae as experimental hosts and in part 

 by rearing on culture media. It is lielieved that the behavior 

 of this nematode is not materially different whether growing on 

 culture media or in the various susceptible insect hosts. 



Japanese beetle grubs acquire their infection by ingesting 

 third stage, infective larvae of the parasite. On reaching the 

 alimentary tract the larvae immediately develop to maturity 

 and copulate. A female will not produce offspring unless fer- 

 tilized by a male. The female is ovoviviparous, eggs hatching 

 within the uterus. Larvae may remain within the uterus and 

 move about for a considerable period but eventually pass out 

 through the vulva one at a time. If a female dies before all 

 larvae are l)orn those remaining may undergo partial develop- 

 ment within the dead body. Each normal-sized female produces 

 a total of aliout 1-" offspring and a generation under optimum 

 conditions requires about ■) to 7 days. By the time the first 

 generation of offspring liave matured the insect is usually 

 dead whereupon its entire body is invaded. The nematodes 

 usuall.v pass through two more generations consuming the car- 

 cass and leaving only a sac formed by the skin and head cap- 

 sule and filled with a thin fluid swarming with larval parasites. 

 In a few cases Glaser was able to infect newlj' killed beetle 

 grubs but he concluded that the nematodes do not enter and 

 multijily as readily in cadavers as in living insects. 



With regard to the virulence of this parasite, Glaser, McCoy 

 and Girth (lit-tO) write that "occasionally an insect Iiost be- 

 comes parasitized very lightly, so that only one nematode be- 

 comes successfully established. This individual may be of either 

 sex, and while if frequently (if not always) causes the death 

 of the host, there is no reproduction." 



McCoy, Girth and Glaser (19.38) report that exceptionally 

 large females of X. glaseri are occasionally found in beetle lar- 

 vae though never on cultures. Such individuals may develop 

 an enormous number of eggs, one giant female producing 1,420 

 larvae. When offsprings of a giant are reared to maturity on 

 cultures only normal sized females are obtained. >rcCoy, Girth 

 and Glaser concluded that fecundation at a late period in de- 

 velopment and abundant food are factors contriliuting to the 

 production of these giant females. 



So long as conditions are favorable and abundant food is 

 availalile, the life cycle of N. glanni, according to Glaser, McCoy 

 and Girth (1940), is completed in three molts the third stage 

 being omitted. When conditions are unfavorable, as when the 

 carcass of the beetle larva has l)een consumed and food is ex- 

 hausted, the young parasites develop into third stage, dauer 

 larvae. At the end of the second stage growth ceases, the ali- 

 mentary tract is emptied, and, as a result of certain niorphologi 

 cal changes, the body becomes more slender. The second molted 



(Utide is retained hcru'c the d.aui r Ijirva is ensheathed though 

 the sheath is not very tenaci(ni8 and may soon be lost. These 

 dauer larvae escape into the soil where they are able to persist, 

 in a more or less .'ictive condition, for at host S'i years. 



• ■l.'L.si'r and his coworkers have reared this lU'inatode success- 

 fully on Petri dish jilates of veal infusion agar flooded with 

 living yeast, on jiofato culture medium, and on veal l>ulp 

 medium. These investigators found that "distiiu't cultural 

 characteristics occur in nematodes from different insect cada- 

 vers, . . . There is a slow decline in fecundity of the cultured 

 nematodes, some 'strains' dying out after .I or 6 transfers, 

 while others continue to yield good cultures after 20 or more 

 ti.-insfers. " If beetle larvae are infected with nematodes from 

 cultures that are dying out .and several generations are passed 

 in the natural host, the nematodes can again be reared success- 

 fully on cultures, the length of time before the cultures again 

 die out depending, to some extent, on the number of genera- 

 tions iiassed in beetle larvae. 



Am.oionkma afpkndicui-atum Schneider, Is.'ill, has on sev- 

 eral occasions been found within the bodies of slugs. Schneider 

 found it originally in Arioii atrr (L.) and Clans (1890), who 

 investigated its life history, secured his material from the same 

 host. The life cycle of this nematode appears to represent a 

 somewhat different line of evolutionary development than the 

 life cycles already discussed. According to Claus (1890), one 

 or more free-living generations alternate with one or more 

 jiarasitic generations, both males and females (Fig. Ifi.'i L & M) 

 developing in each instance. Individuals of the parasitic gener- 

 ations leave the host .inst before reaching maturity by boring 

 their way out through the foot. On reaching the exterior they 

 nuifure, copulate and produce progeny that usually develop as 

 free-living individuals. Maupas (1899) found that larvae of 

 the free-living generation undergo the usual four molts and 

 reach maturity in about 3'4 days. 



A regular alternation of a free-living with a parasitic gen- 

 eration does not necessarily follow, however, as there may be 

 several consecutive free-living or several consecutive parasitic 

 generations. There are usually consecutive free-living genera- 

 tions as long as conditions are favorable but when conditions 

 become unfavorable the nematodes "encyst" and these "en- 

 cysted" larvae will continue development only when taken into 

 the bod.v of a slug. According to Maupas, "encysted" larvae 

 that fail to gain entrance to a slug become exhausted and die 

 in about 4 months. Precisely how the nematodes enter the slugs 

 and wlietlier or not, in event of consecutive parasitic genera- 

 tions, females mature without leaving the host, are points that 

 seem to need further elucidation. 



Claus found certain morphological differences between corre- 

 sponding stages of the two generations. Adults of the parasitic 

 generations are much larger than adults of the free-living gen- 

 erations and parasitic larvae, in the later stages of develop- 

 ment, are said to possess two long, ribbon-like, caudal append- 

 ages not present on free-living larvae of the corresponding 

 stage. 



Other Species. Diplogaster labiala Cobb (in Merrill and 

 Ford, 1916) was found in the elm borer, Saperda tridciitala 

 Oliv., collected near Manhattan, Kansas. This nematode repro- 

 duces in the intestine of the living, adult liorer and may ac- 

 cumulate in sufficient numbers to rupture the gut and kill the 

 insect. Infected female beetles are usuall.v sterile. When reared 

 on cultures, Merrill and Ford (1916) found that eggs hatched 

 in from 30 to 32 hours and the nematodes matured in 7 to 10 

 days. Oviposition began from 2 to 4 hours after copulation and 

 lasted for about 2 days with an average output of^ seven eggs 

 per female. Only a few individuals were seen copulating a sec- 

 ond time. Apparently dauer larvae (Fig. lO."! K) develop when 

 conditions are unfavorable. 



Xcoaplectana affinis, Bovien, 1937, was found in Denmark 

 where it infects larvae of the same insects that harbor Neoaplrc- 

 lann bibinni.s, i.e., Bibio fcrnif/iiiatii.s, B. hort iilanifs and VUo- 

 pitus vuli/aris. These two nematodes were differentiated mor- 

 phologically by Bovien (1937) only on the basis of males and 

 dauer larvae, the life cycles and behavior of the two being al- 

 most identical. Bovien made one observation, however, that de- 

 serves mention. When in the intestine of any of its three nat- 

 ural hosts mentioned above, .V. affinifi remained in the dauer 

 stage and was apparently innocuous so long as the insect re- 

 mained alive. When two larvae of a beetle, Tcirplwru.i sp., 

 were experimcntall.v infected, they became moribund in a few 

 days and dissection revealed several adult and prcadult nema- 

 todes in the body cavity of each beetle. This observation sug- 

 gests that whether or not A', affinis remains passively in the 

 intestines depends on the insect involved. 



A mode of life on the border line between saprophagous and 

 parasitic is characteristic of other nematodes, probably of a 

 considerable number. Other species of Neoapleclana are known 

 to exist but life cycles have not been investigated. Steincrncvxa 



249 



