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Insect Control Questions

Question 1

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Answer 1

Insects are a source of organic carbon, and so are attractive to heterotrophic fungi as a source of nutrition. While new defences are evolving in insects to prevent damage by fungi, the fungi with a faster life cycle are also under selection pressure to overcome insect defences.

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Question 2

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Answer 2

Penetration of insects by fungi can be via the exoskeleton or the mouth. When penetrating the exoskeleton, fungi use digestion and pressure to pass through the outer layer. One common constituent of both insects and fungi is chitin. However, in the fungi, chitin is only a small proportion of the wall constituents. Thus excretion of chitinases need not cause significant harm provided it is directed to the exoskeleton and not dispersed. Enzymes are commonly used to assist penetration, they are not the sole mechanism. The enzyme is likely to loosen the fibrillar structure of the exoskeleton. Pressure from the fungus is likely to enable the fungus to then penetrate between remaining fibrils and enter the insect. Just as hyperparasitic fungi excrete chitinase against other fungi, it can be used to assist penetration of the insect carapace.

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Question 3

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Answer 3

Many factors reduce chances of effective biocontrol. The first stage, contact and penetration, is probably where most difficulties exist. Fungi require appropriate environmental conditions for germination and penetration of the insect. In air, where most attempts at biocontrol take place, the humidity is commonly low, fungi are subject to UV radiation and spores are carried with air currents and need not contact the insect easily. Low humidity prevents germination, UV damages the nuclei when the germ tubes emerge, and the spore is commonly so light that impact with the insect is unlikely. Soil-borne insects are less commonly noticed, and even there, chances of contact are low. It is only when insects are present in plague proportions that biocontrol becomes “easy”.

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Question 4

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Question 5

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Question 6

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Question 7

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