The results of 4 different assays for haemocytic immune responsiveness in the cockroach, Periplaneta americana, have shown that the presence of larvae of Moniliformis moniliformis within the haemocoele depresses the insect's immune reactivity. Thus, the proportion of haemocytes that phagocytose fluorescent latex beads in vivo, the proportion of haemocytes that can be stimulated in vitro by the β1,3-glucan, laminarin, to produce phenoloxidase, and the number of haemocytic aggregates produced in vivo in response to zymosan stimulation, are significantly depressed compared with control, unparasitized cockroaches. Also, when cockroaches are injected intra-haemocoelically with hatched oncospheres of the tapeworm, Hymenolepis diminuta, a higher prevalence and intensity of tapeworm larvae are found in insects already parasitized by M. moniliformis. All of these assays show that depression rather than total suppression of the immune response occurs; in the wild, this may be sufficient to ensure that the cockroach does not succumb to unrelated infections during the long developmental period of the parasite.

At field rates (ca 0·1–10 μg active ingredient/ml), non-fumigant nematicides such as oxamyl do not kill plant-parasitic nematodes directly but act by impairing neuromuscular activity. The present study has shown that neutral lipid levels in 2nd-stage (infective) juveniles of Globodera rostochiensis, which had been incubated with the oximecarbamate nematicide oxamyl (1 μg a.i./ml) for between 8 and 35 days, were significantly (P < 0·05) greater when compared with controls maintained in water alone. The difference between treatments was found to be due principally to changes in the lipid content in the posterior half of the body which appears to act as the major long-term lipid store. When nematodes were allowed to recover for 72 h following incubation for 35 days with oxamyl, their infectivity was not significantly (P > 0·05) different from that of controls. This work is discussed in relation to the action of oxamyl and similar nematicides and to the use of controlled-release formulations as a means of increasing their efficacy.

The invasion and establishment of Heterodera glycines has been studied for 0–120 h after addition to host roots using a synchronized infection system. A high degree of synchrony in development was noted, with juvenile nematodes reaching their feeding sites adjacent to the root endodermis and discharging their subventral pharyngeal glands by 24 h post-invasion (p.i.). The moult to the 3rd-stage juvenile occurred approximately 89 h after entry to the root. Using an enzyme-linked immunosorbent assay with monoclonal antibodies (MAbs) whose tissue specificities had already been defined by immuno-cytochemistry, it was found that MAbs recognizing intestinal lipid droplets and granules showed a major increase in reactivity 18–24 h p.i. before declining by 39 h p.i. In contrast, the reactivity of two MAbs recognizing adult cuticle increased significantly only after 89 h p.i., following the second moult. MAbs to the two subventral pharyngeal gland cells showed a variety of patterns of changing reactivity during the experiment. One increased within 24 h of invasion before declining whereas a second fell without any initial rise. Two further MAbs specific for the subventral glands initially declined but showed a secondary increase in reactivity after 72 h and could be detected in adult females. This pattern was also seen in a MAb specific for the dorsal pharyngeal gland cell. These changes are discussed in the context of events taking place following invasion, with particular reference to the initiation and maintenance of a feeding syncytium by the developing nematode.

The influence of various agents on the adhesion of endospores of Pasteuria penetrans to the nematode Meloidogyne javanica was studied. Similarly, but to a lesser degree, we have also studied the adhesion of conidia of the fungus Dilophospora alopecuri and the coryneform bacterium Clavibacter sp. (syn. Corynebacterium rathayi) to the nematode Anguina agrostis (syn. A. funesta). Reduction in the degree of both spore and conidial attachment following their pre-treatment with periodate and the presence of PAS staining material on spores, conidia and bacteria implicated carbohydrate in these interactions. Tests involving both unbound and FITC-bound lectins demonstrated that wheat germ agglutinin (WGA) can inhibit the degree of attachment of P. penetrans to M. javanica and that this inhibition can be overcome by pre-treatment of the lectin with N, N′-diacetyl chitobiose. Endospores of P. penetrans, amphid and buccal secretions of 2nd-stage larvae of M. javanica and the cuticle and excretory pore secretions of 2nd-stage dauer larvae of A. agrostis bound WGA, indicating that accessible N-acetyl-D-glucosamine residues are present on these structures. Endospores of P. penetrans also bound Con A, indicating the presence of accessible α-D-glucose/α-D-mannose residues on their surface.

Resistance developed by the immune system in response to blood-stage malaria is complex in nature, involving humoral and non-antibody effector mechnisms. Different species of malarial parasites may vary in their ability to elicit, or their susceptibility to, those immune effectors. This complexity is enhanced by the different results obtained in vaccinated as opposed to drug-controlled infections. It is therefore important that some attempt be made to unravel these interactions. This is particularly so when we have to decide on methods for assessing the potentiality of antigens to induce protective immunity. In this review the limitations of some in vitro assays of immunity, as well as those of various host–parasite models, are discussed. The relative importance of cell-mediated and humoral immunity in laboratory models and natural infections is also considered in the context of vaccine development.

Maturity, mass and sex were determined for individual Raphidascaris acus from northern pike, Esox lucius from Dauphin Lake, Manitoba. Length, width and total fecundity of female worms; seasonal changes in worm numbers, growth and maturity; and inequalities in mass and fecundity were quantified for 8 sample periods between April and September. Recruitment of R. acus is most rapid in early spring and continues throughout summer. An accumulation of larvae over winter leads to a peak in the number of gravid worms in spring, while increased feeding by post-spawning pike on yellow perch, Perca fluviatilis, leads to lower levels of gravid worms throughout summer and early autumn. Gravid worms found in spring versus summer were similar with respect to all measured variables and do not appear to be from genetically distinct populations. The strength of the correlation between fecundity and mass for worms was variable between pike and between sample periods, and only weakly correlated when the data were pooled. Much of this variation could be attributed to continued growth of gravid worms after maturation. Worms found in June were smaller, less fecund and less variable and inequalities in mass and fecundity measured using Gini coefficients (GCs) and Lorenz curves (LCs) were most similar at this time. For all other sample periods inequality in fecundity was greater than the corresponding value for mass. Similarity between GCs based on mass and fecundity was maximum when the coefficient of variation (C.V.) for mass was greater than the corresponding C.V. for fecundity. These observations suggest that one must be cautious when applying GCs and LCs to the analysis of parasite populations.