curs ill the north i-oiitrnl and northoastorii Uiiitod States wiicrc 

 it is a common parasite of grasshoppers inoUidinR both Acridi- 

 dae and TotliKouiidae. It sometinioa iiifeets crickets (drylli- 

 dae) and has been found, occasionally, in leaf hoppers and 

 beetles. The life history of this merinithid was studied by 

 Christie (I'.KiG) upon whose work tlie following account is based 

 and which applies to the soil and climatic conditions of north- 

 eastern Virginia. 



The free living stages of this nematode occnjiy small cavities 

 in the soil usually from ."> to 15 cm. below the surface (proliably 

 deeper in sandy or loose soil). When inhabited by .'idults each 

 cavity, almost without exception, contains one female aiul sov 

 eral males, generally two or three, sometimes as many as eight, 

 coiled and intertwined to form a "knot." Copulation is neces- 

 sary and females reared in the absence of males fail to lay 

 eggs. Egg laying begins about the first of July, continues until 

 interrupted by the advent of cold weather, and eggs (Fig. 

 108 ,1 & K) accumulate over the surface of the soil cavities and 

 over the parent nematodes. For the most part eggs laid during 

 a given summer do not hatch until the following spring. Cleav 

 ago and embryonic development take place after deposition and 

 the first molt occurs within the egg shell. 



At the time of hatching the second stage larva is immediately 

 infective. The body, which shows a high degree of organiza- 

 tion and development, is divided into two parts by the node 

 (Fig. 1()8 LV In the anterior part, which constitutes about 

 one fifth of the total length, one finds most of the organs com- 

 mon to nematodes including esophagus and esophageal glands, 

 intestine, nerve ring, and excretory pore. The posterior part 

 of the body serves as a propelling and food storage organ and 

 contains a row of cylindrical cells, probably modified intestinal 

 cells. An anus is apparently lacking. 



During late fall and winter a female is surrounded by her 

 total egg output of the season. Egg counts on six females 

 made during the winter showed the total number of eggs present 

 to vary from L!,(>2."i to 6,.530. As will be noted later, a female 

 lays eggs during two summers hence these figures represent 

 roughl.v about half the total egg output. 



Although some larvae may begin to emerge from the eggs 

 fairly early in spring, a greater part of them hatch during a 

 short period at about the middle to the latter part of June. The 

 species of grasshoppers that mo.st commonly serve as hosts 

 (Mclanoplus fcmurrtibrum and Conoccphalns brcvipennis (Scud- 

 der) in northeastern Virginia) also hatch at about this time. 

 The larval nematodes migrate to the surface of the soil and 

 climb grass and other low vegetation when it is wet with dew 

 or rain. They seek newly hatched grasshopper nymphs and 

 enter their body cavity by penetrating the body wall. Pene- 

 tration takes place under the edges of the pronotum, between 

 the abdominal segments, or at other places where the chitinous 

 covering is thin. Penetration is effected by the use of the 

 stylet probably aided by the dissolving action of a chitin sol- 

 vent secreted by one or more of the most anterior esophageal 

 glands. 



After the anterior end is inserted into the host the body of 

 the larva breaks at the node and the postnodal portion is left 

 on the outside. If the body fails to break, as occasionally hap- 

 pens, the postnodal part undergoes no development in the host 

 but remains as a vestigeal appendage that eventually sloughs 

 off. The nodal scar (Fig. 93, p. 89) persists throughout the 

 parasitic stage as convincing evidence that no molt takes place 

 during this period. The number of parasites per host is 

 usually one (Fig. 168 M), sometimes two, rarely three or more. 



Ouee inside the body cavity of the host the parasite under- 

 goes a period of phenomenal growth accompanied by pro- 

 nounced morphological changes. The stychocytes (see p. 92) 

 arc a conspicuous anatomical feature of larvae that have been 

 in the host from 4 to 10 days (Fig. 93, p. 89). As the body 

 increases rapidly in length it becomes filled by the intestine, 

 in fact intestinal tissue eventually fills all available space not 

 occupied by other organs even growing past the base of the 

 esophagus and extending into the neck region. Apparently 

 this modified intestine performs no digestive function but serves 

 as a reservoir for nutrient materials. Males remain in the 

 host for from 1 to 1V> months and females from 2 to 3 

 months. The mermithids emerge head foremost forcing their 

 way through the body wall between the segments, fall to the 

 surface of the ground, and enter the soil. 



During the first winter in the soil males and females remain 

 isolated each individual forming a separate "knot." The final 

 molt takes place the following spring about the latter part of 

 June and at this time males seek the females. It will be noted 

 that only two molts have been observed. Egg laying begins 

 soon after the final molt, usually about the first of .Tuly, and 

 continues until interrupted by cold weather. The following 

 spring a year-old female begins laying eggs slightly earlier 

 than one that has just molted. By the end of the second sum- 



mer of egg laying the reserve food has become exhausted and 

 the transparency of the body is in sharp contrast to its 

 opaqueness at the time of emergence from the host. Most fe- 

 males probably fail to survive a third winter in the soil. In- 

 formation regarding the longevity of males is not very satis- 

 factory but it seems probable that they live for about the same 

 length of time as females. 



.1. ilccaudala causes no noticeable change in the external 

 anatiiMiy of grasshoppers. Infected individuals sometimes have 

 distended abdonu'us and are likely to apjicar sluggish, adults 

 being incapable of suslaimnl flight. The most pronounced ef- 

 fect of this parasite is on the gonads of the host (Fig. 109 A 

 & B). It is doubtful if infected female grasshoppers are capa- 

 ble of laying eggs as the ovaries are always greatly reduced in 

 size. The effect on the testes is less pronounced and infected 

 male grasshoppers have been observed in copula. The cme>-g- 

 gence of the parasite invariably results in the death of the host. 



Mekmis siJHNiORKSCf;NS Cobb, 1930, appears to be strictly a 

 grasshopper parasite. It occurs in the United States over about 

 the same range as Affajnermis drcaudala where it has been 

 found infecting nine different species of grasshoppers including 

 both Acrididae and Teltigoniidae. Several other species have 



H -~- ^^^-x^ ^— G 



Fig. 169. EFFECTS OF MERMITHIDS ON THEIR HOSTS 



A & B — Dissections of adult female grasshoppers, Melanoplus femur- 

 rub rum, showing reproductive organs (A — Normal grasshopper; B — 

 Grasshopper parasitized by Agamennis decaudata) . gas cne, gastric 

 caeca ; int, intestine ; o i% ovary ; ovd, oviduct ; spthc, spermatheca. 

 & D — Females of the ant. Lasius alienus (C — Normal female: D — Fe- 

 male parasitized by Allomermis mermicophyla, i.e., a mermithogyne). 

 E-G — The ant, Pheidole absurda (E — Individual parasitized by a mer- 

 mithid, i.e., a mermithergate; F — Normal worker; G — Normal soldier). 

 H — The ant, Pheidole f/auldi, a mermithergate. A & B, after Christie, 

 1936; C & D. after Crawley and Baylis. 1921; E-G, from Wheeler, 

 1928, after Emery; H^ after Wheeler. 1928. 



2.15 



