Au^usr September 



Fig. 170a. LIFE CYCLE OF AGAilERillfi DECAUDATA 



Diagram illustrating 12-month period, August to July, inclusive. ". 

 "knot" composed of one female and several males that emerged froni 

 hosts 2 years previous to beginning of period represented, b. "knot" 

 composed of one female and several males that emerged from hosts 1 

 year previous to period represented. Mermithids that would emerge 

 during September and October of period represented are omitted for 

 simplicity. Female in "knot" a has, by October, completed its second 

 summer "of egg laying and dies during ensuing winter but the accumu- 

 lated eggs, deposited during previous summer, hatch May to June. Fe- 

 male in "knot" ii has, by October, completed its first summer of egg 

 laying and the accumulated eggs hatch May to June while the second 

 summer of egg laying is begun during May. 



been experimentally infected. Attempts to infect other insects 

 including crickets (Gryllidae), mole crickets (Gryllotalpinae), 

 and larvae of several species of Lepidoptera have been unsuc- 

 cessful. The following account of the life history is based on 

 investigations by Christie (1937) conducted, for the most part, 

 in Massachusetts. 



Grasshoppers become infected with .1/. siibnigrescens by swal- 

 lowing the eggs. In order to bring this about the egg-laying 

 habits of this nematode are radically different from those of 

 Againer7nis decaudata, otherwise the two life cycles are some- 

 what similar. Eggs of .V. siibnigrescens are never laid in the 

 soil. Gravid females climb low vegetation on which they lay 

 their eggs (Fig. 168 N) and to which the eggs cling l)y means 

 of the entangling appendages or bissi. 



The egg, when deposited, contains a fully developed infec- 

 tive larva (Fig. 140 B, p. ISl). The shell proper is protected 

 by an outer covering that is divided into two cup-like halves 

 by a groove at the equator (Fig. 14(1 A, p. ISl). At each pole 

 there is a raised or thickened area formed by the attachment 

 of the entangling appendages (Fig. 139, p. 181). The outer 

 covering breaks apart along the groove at the equator and the 

 two cup-like halves are easily removed. In the shell proper 

 there are two opposite areas at the equator where the color is 

 lighter than elsewhere and these areas are partly dissolved by 

 the digestive action of the host thus facilitating the escape of 

 the larva. Botli the outer covering and the shell proper con- 

 tain brown pigment, presumably to protect the larva from the 

 action of sunlight. Eggs deposited on foliage remain viable 

 throughout the summer. When eggs were kept experimentally 

 in a moist chamber sonic remained viable for a year. 



When an egg reaches the alimentary tract of its host the 

 outer covering has usually been rubbed off. The two opposite 

 areas of the shell at the equator gradually become clearer and 

 begin to protrude until they appear as colorless hemispherical 

 projections (Fig. 140 C, p. 181) that finally rupture and pro- 

 vide openings for the escape of the larva. The larva itself does 

 not appear to aid in its own liberation. Wlien first freed it is 

 rather sluggish but soon becomes active, penetrates the wall of 

 the gut and enters the body cavity. Penetration through the 

 intestinal wall is aided by the stylet which is rhythmically pro- 

 truded. 



From 1 to 5 parasites per host is the number most frequently 

 encountered but there is great variation and grasshoppers har- 

 boring 100 or more parasites of widely different ages are not 

 uncommon in some localities. As a nymph grows older and its 

 food consumption increases, its chance of becoming infected 

 is correspondingly greater. The sex ratio of M. siibnigrescens 

 is intluenced by the number of parasites per host. When a 

 grasshopper harbors a large number, all develop into males but 

 when a grasshopper harbors only 1 or 2 these usually develop 

 into females (Christie, 1929). 



The parasitic development of M. siibiiignscens is essentially 

 the same as that of Agamcrmis decaudata. There is the same 

 rapid increase in size and the same extensive proliferation of 

 intestinal tissue. Males remain in the host from 4 to 6 weeks 

 and females from 8 to 10 weeks. At the end of this time the 

 parasites force their way through the body wall of the host 

 and enter the soil. When a grasshopper harbors parasites of 

 different ages, all that are too immature to escape and survive 

 in the soil perish with the host when the older ones emerge. 



June 



Postparasitic individuals of M. siibnigrescens are found in the 

 soil down to about 60 cm., the majority occurring from 15 to 4.1 

 cm. below the surface. They usually remain isolated and one 

 larely finds a "knot'' composed of a female and one or more 

 males as is characteristic of Againerniis decaudata. Most in- 

 dividuals emerge from the host during summer and autumn 

 and molt the following April. This is the final molt and the 

 only one that has been observed. Copulation may take place 

 and has been seen on several occasions but copulation is not 

 necessary as females reared in the absence of males produce 

 viable eggs. By July females begin to exhibit a brownish color 

 due to accumulating eggs and by September they are nearly 

 Iilack except for a short region at each extremity of the body. 

 At this time most of the eggs are viable but they are not laid 

 until the following spring. Before ovipositing, a gravid female 

 8") mm. long contains about 14,000 eggs. 



Egg laying usually begins in May and may continue through- 

 out July or even into August, depending on weather condi- 

 tions. Eggs are laid during rain and should the early summer 

 months be dry egg laying will be delayed. Gravid females 

 climb grass and other low vegetation over which they con- 

 stantly move while eggs are being laid. If rain continues egg 

 deposition goes on throughout the day but if the rain stops 

 and the foliage becomes dry females coil up, fall to the sur- 

 face of the ground and enter the soil, presumalily to resume egg 

 laying during the next rain. 



It is not known how long females live after the uteri are 

 emptied of eggs but by this time their stored food is nearly 

 exhausted and it seems highly improbable that the.v are able to 

 survive a third winter or to develop more eggs. However, if 

 prevented from coming to the surface to deposit eggs they are 

 able to survive a third winter and to lay eggs the following 

 spring. Females that normally would have deposited eggs in 

 1932 were buried in containers and prevented from coming to 

 the surface (Christie, 1937). When examined during May, 

 1933, many of these females were alive, in good condition, and 

 filled with eggs. There was no evidence tliat eggs had Ijeen 

 deposited, although these females promptly began laying eggs 

 when brought to the surface and placed in the light. 



Apparently eggs are not laid at night. Egg laying is con- 

 trolled, at least in part, by light stimuli. When an ovipositing 

 female is placed in the dark, egg laying promptly stops, but is 

 resumed just as promptly when the female is again placed in 

 the light. The head of the adult female is colored with areas 

 of reddish brown pigment which, presumably, is an organ for 

 light perception. The male, which never comes to the surface, 

 lacks this pigment. 



Merniis siibnigrescens has about the same effects on its host 

 as does Agamcrmis decaudata. These effects are suppression 

 of the gonads, especially the ovaries, and death of the host 

 when the parasite emerges. With If. subnigresccns the effect 

 on the gonads of the host is much more variable than with A. 

 decaudata due to variations in the nnmlier of parasites per host 

 and the time the parasites are acquired. 



.-VLLANTONEMATIDAE 



The Allantonematidae is a group of insect parasites that are 

 closely related to the preeminently plant-infecting Tylenchidae. 

 The species that have been studied and named jnobably con- 

 stitute but a small part of the number that exist but in nearly 

 every instance where the life cycle is known it follows the same 

 genera! plan and differs from that found in any other group of 

 nematodes. 



Adult gravid females occupy the body cavity (haemocoel) of 

 the insect, frequently in small numbers, often one per host. 

 Here larvae accumulate and develop to a certain stage, molting 

 at least once (probably twice in most species) ; then they escape 

 from the host either by entering the alimentary tract and pass- 

 ing out through the anus or by entering the female reproductive 

 system and passing out thi'ough the genital aperture. Most 

 species infect both males and females of their host insect. In 

 some eases the only known way by which larvae are able to 



