Ncu

718 host, the gypsy moth (Lymantria dispar)], N. polyvora [imported cabbageworm (Pieris brassicae)], N. pyrausta [European corn borer (Ostrinia nubilalis)], andN. locustae (almost 60 species of Orthoptera) (Maddox, 1987).

Though some pathogenic protozoa would seem to be good candidates for biological control agents, research into this possibility is proceeding slowly, primarily because, with few exceptions, the pathogens cannot be cultured outside their host. As a result, obtaining sufficient spore material for testing is somewhat slow.

5.2.6. Nematodes

Though obviously not microorganisms sensu stricto, nematodes are generally included in this term in discussions of insect pathogens. Nematodes enter into a variety of interactions with insects, including parasitism, and pathogenesis, and are important natural regulators of insect populations (Kaya et al., 1993).

Most insect-associated nematodes are parasitic and in most instances do not directly cause death but, rather, protracted larval development, abnormal morphology (including wing shortening), and reduced fecundity. Many of the effects noted can be attributed to debilitation of the host as the nematode feeds on its tissues, especially fat body. Other effects result from more specific activities on the part of the parasite. For example, some morphological abnormalities probably result from endocrine imbalances, induced perhaps by toxins released by the parasite. Sterility results in some insects because the parasite selectively feeds on the gonads.

Pathogenic nematodes are found in only two small, monogeneric families, Stein-ernematidae (14 recognized species of Steinernema) and Heterorhabditidae (5 species of Heterorhabditis) (Kaya et al., 1993). Members of these families are unique in that: (1) they are the only nematodes with the ability to carry and introduce symbiotic bacteria into the host insect's body cavity; (2) they are the only insect pathogens with a host range that includes most insect orders and families; and (3) they can be cultured on a large scale in artificial media (Poinar, 1990). The bacteria (Xenorhabdus spp.) are carried in the intestine of the nematode and are released into the hemocoel when the infective (juvenile) nematode enters the insect through the mouth, anus, spiracles, or body wall if the cuticle is thin. The bacteria propagate rapidly, typically killing the host insect within 48 hours as a result of septicemia. However, studies have also shown that some nematodes are pathogenic even in the absence of the bacteria, indicating that the nematodes produce toxins. The nematodes feed on the bacteria, mature, and produce up to 105 offspring that emerge as infective juveniles (Akhurst and Dunphy, 1993; Kaya and Gaugler, 1993).

Soil is the normal environment for entomopathogenic nematodes, which would therefore be expected to have a restricted host range and limited potential as microbial pest-control agents. However, under laboratory conditions they are capable of infecting a very wide range of insects, including mosquitoes, black flies, grasshoppers, caterpillars, weevils, and ants, opening the way to the possibility of developing nematode-based management systems for certain above-ground pests.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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