Secretions from glands, parasitic

Secretions from Glands and Other Specialized Tissues. In general, parasitic Hymenoptera are known to inject secretions from glands and specialized tissues into their hosts. Those secretions, except for the symbiotic viruses and virus material or calyx fluid, are collectively presented in the next two sections as venomous substances. 

Fig. 18.3. A cercaria of Schistosoma mansoni penetrating the skin epidermis. The parasite has traversed the outer skin layer, stratum corneum (SC), and is halfway through the underlying dermis, stratum basale (SB). Movement through these layers is facilitated by proteases, most particularly an elastase, which is secreted from the cercarial acetabular glands. The cercaria is moving, as indicated by the arrow, into the inner skin layers where it will meet and enter a venule.

Waxes also serve a diversity of other functions related to their water-repellent properties and their firm consistency. Certain skin glands of vertebrates secrete waxes to protect hair and skin and keep it pliable, lubricated, and waterproof. Birds, particularly waterfowl, secrete waxes from their preen glands to keep their feathers water-repellent. The shiny leaves of holly, rhododendrons, poison ivy, and many tropical plants are coated with a thick layer of waxes, which prevents excessive evaporation of water and protects against parasites. 

Similarly, parasitism of P. separata, by A. kariyai or injection of the calyx fluid or virus material from the parasitoid, caused a decline in the host ecdysteroid titer and arrested metamorphosis of the host (54). Again, injection of exogenous 20-hydroxyecdysone reversed the developmental arrest. In this case, administration of prothoracicotropic hormone caused a reactivation of the prothoracic glands in the treated host. These results showed that the virus material inhibited the synthesis or secretion of prothoracicotropic hormone and also lowered the ecdysteroid level in the host. Also in this case, a mixture of both venom and calyx fluid were needed to obtain the full prolongation of the larval stage in the host (110). 

Dimethylquinazoline is from Triatoma bugs which carry trypanosomiasis parasites, and indole and skatole are evil-smelling compounds found as trail pheromones in ants and defensive secretion of caddis flies (Trichoptera). Methyl anthranilate has been found in the mandibular gland of males of the ant Camponotus nearticus, and is one component of the trail pheromone (with methyl nicotinate) of the ant Aenictus rotundatus. 

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