Larval Maturation

Larval maturation studies, sometimes referred to as cultures, can be performed on fecal specimens applied to wet filter paper. Nematode larvae such as Strongyloides spp. or hookworm mature to the filariform stages in the culture container and migrate from feces into water, where they are detected microscopically. The procedure can be performed in a petri dish with a square of filter paper or in a large test tube with a strip of filter paper. 

(a) For the tube method, insert the filter paper strip into the tube so that the bottom of the strip is in 3 ml of water. The feces-smeared portion of the strip need not be immersed in the water. 

Leave the tube or dish at room temperature in the dark. Add water as needed to ensure that the filter paper is in contact with the water. 

Examine the liquid for larvae either by direct microscopic 

Examine the specimen on days 3, 5, and 7. Strongyloides filariform larvae are found on days 2 and 3, and hookworm larvae are found on days 5 through 7. Larvae are identified by their morphological characteristics. 

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Both the adult and the larval cysticerci (bladderworm) of Taenia solium (pork tapeworm) are able to Hve in humans the parasite is found sporadically in uncooked pork. In the stomach, the larva is digested out of the pork flesh it then grows and attaches to the wall of the small intestine. Maturity is reached in 5—12 weeks. The adult is 5 m long, and untreated adult worms may survive for 25 years. 

Neanthes arenaceodentata is the most sensitive marine organism yet tested. In worms exposed to sublethal concentrations of CC6, feeding was disrupted after 14 days at 79 pg/L (USEPA 1980), reproduction ceased after 440 days (three generations) at 100 pg/L (Oshida et al. 1981), brood size was reduced after 309 to 440 days at 12.5 to 16.0 pg/L (Oshida et al. 1981 Oshida and Word 1982), and abnormalities in larval development increased after 5 months at 25 pg/L (Reish 1977). On the other hand, exposure for 293 days (two generations) in 50,400 pg Cr+3/L caused no adverse effects on survival, maturation time required for spawning, or brood size (Oshida et al. 1981). The poly-chaete Capitella capitata was more resistant than Neanthes, a decrease in brood size was noted only after exposure for 5 months to 50 and 100 pg Cr+6/L (USEPA 1980). 

In the laboratory as well as in the field, larval waterborne stimuli attracted sexually immature males and females. (The field tests were run from 22 00 to 04 00 hours, the activity time of migrating lampreys.) Certain conditions have to be met the fish responded only early in the night, and before being fully sexually mature. 

Closantel is used primarily in cattle and sheep for treatment of mature and immature liver flukes, hematophagous nematodes, and larval stages of some arthropods. It is administered orally or parenterally at dosages of 5-15 or 2.5-7.5 mg/kg bw, respectively. Closantel does not exhibit carcinogenic, teratogenic, or embryotoxic activities. 

JUNVENILE HORMONES. One of several hormones, that retard the development of insects in the larval stage. So called because they prevent the insect from maturing by maintaining its juvenile characteristics. Obtained naturally from silk moths various syntheses indicate possible use as insecticides, especially for fire ants. Composition of one type is C18H30O3. 

Assembly and Maturation of the Drosophila Larval Neuromuscular Junction E Sian Gramates and Vivian Budnik... 

Table 4.7. Total lipid content and neutral lipid fractions identified in mature and larval cestodes. (Data from Frayha Smyth, 1983 Barrett,...

The process of hatching in the Cyclophyllidea, which results in the release of the oncosphere, has been discussed in Chapter 7. The basic structure of a mature oncosphere (Fig. 8.16), which will not be discussed in detail here, does not vary substantially between species. It is composed essentially of (a) a thin covering epithelium with cytoplasmic extensions, (b) an additional complex system of muscles operating the three pairs of hooks, (c) a pair of large penetration glands, (d) a small core of germinative cells from which the next larval stage develops and (e) a primitive nervous system. 

By the use of larval cestodes as initial material, the following species have been cultured in vitro to maturity or near maturity. 

Maturation of larval pseudophyllidean cestodes and strigeid trematodes under axenic conditions the significance of nutri-... 

Another developmental hormone is the juvenile hormone, which predominates early in larval life later ecdysone predominates. It is a methyl ester of the epoxide of a fatty acid derivative, and there is some evidence that its structure differs in different groups of insects. By a series of coincidences, it was discovered that certain paper toweling prevented the European bug, Pyrrhocoris apterus, from developing into sexually mature adults. Instead, an extra one or two larval molts ensued, and all eventually died without being able to complete metamorphosis. The juvenility factor was traced to particular conifers used in American paper pulp, mainly Abies balsamea, Tsuga canadensis, Taxus brevifolia, and Larix laricina. The active principle was isolated and characterized. It... 

In essence, sea urchin larval spicule formation takes place in a preformed membrane framework that continuously changes. There is, however, also an organic matrix-like framework within the spiculogenic cavity. It is composed of polysaccharides and proteins that remain insoluble after the mineral phase of the mature spicule is dissolved [75]. The framework forms concentric sheaths around the spicule long axis, and has radiating fibers that connect the sheaths laterally. It is not, however, known whether this matrix is preformed and functions as a framework to guide the mineral deposition, or whether it is deposited periodically as the mineral is introduced. 

Development rate (e.g. time for larval development, time to maturity) ... 

Among natural populations, two major deviations from the ideal pattern are ubiquitous (Pielou, 1977 Lerman, 1979). The first deviation consists of populations with excessive proportions of young units (e.g., planktonic larval stages) because their destruction rate is very high, but chances for survival improve considerably with maturation (type II in Figure 2). The mathematical formalism for such populations (e.g., Lerman, 1979) is a power-law function. 

Neem (Azadirachta indica). This interesting seed oil contains chemicals used to control 200 species of insects. The oil prevents some insect species from maturing past the larval stage (144). 

Neoteny—Retention of larval or juvenile characteristics in a sexually mature adult. 

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