Biological control of aphids by coccinellid beetles Biological control of aphids by coccinellid beetles. (After Burton & Burton 1975.)
Figure 16.1 Schematic graphs of the fluctuations of theoretical insect populations in relation to their general equilibrium population (GEP), economic threshold (ET), and economic injury level (EIL). From comparison of the general equilibrium density with the ET and EIL, insect populations can be classified as: (a) non-economic pests if population densities never exceed the ET or EIL; (b) occasional pests if population densities exceed the ET and EIL only under special circumstances; (c) perennial pests if the general equilibrium population is close to the ET so that the ET and EIL are exceeded frequently; or (d) severe or key pests if population densities always are higher than the ET and EIL. In practice, as indicated here, control measures are instigated before the EIL is reached. (After Stern et al. 1959.)
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Figure 16.2 Cumulative increase in the number of arthropod species (mostly insects and mites) known to be resistant to one or more insecticides up to year 2000; the number has increased since then. (After Bills et al. 2000.)
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Figure 16.3 Generalized life cycle of an egg parasitoid. A tiny female wasp of a Trichogramma species (Hymenoptera: Trichogrammatidae) oviposits into a lepidopteran egg; the wasp larva develops within the host egg, pupates, and emerges as an adult, often with the full life cycle taking only 1 week. (After van den Bosch & Hagen 1966.)
Figure 16.4 The mode of infection of insect larvae by baculoviruses. (a) A caterpillar of the cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae), ingests the viral inclusion bodies of a granulosis virus (called TnGV) with its food and the inclusion bodies dissolve in the alkaline midgut, releasing proteins that destroy the insect’s peritrophic membrane and allowing the virions access to the midgut epithelial cells. (b) A granulosis virus inclusion body with virion in longitudinal section. (c) A virion attaches to a microvillus of a midgut cell, where the nucleocapsid discards its envelope, enters the cell, and moves to the nucleus in which the viral DNA replicates. The newly synthesized virions then invade the hemocoel of the caterpillar where viral inclusion bodies are formed in other tissues (not shown). (After Entwistle & Evans 1985; Beard 1989.)
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