There is no such thing, as a number plants contain toxins/repellents to naturally protect from any (or at least most) pests. Locusts are known for destroying large areas of crops in massive swarms and far as I know are one of the top candidates for describing what you are asking (if I'm understanding the question that is).
Locust swarms devastate crops and cause major agricultural damage and attendant human misery like famine and starvation. They occur in many parts of the world, but today locusts are most destructive in the sustenance farming regions of Africa, the desert locust in particular. Found mainly in equatorial regions, they inhabit some 60 countries and can cover one fifth of the Earth's land surface. Desert locust plagues may threaten the economic livelihood of one tenth of the world's humans.
An insect that starts with an "H," is brightly colored, and eats crops is a hornet. They are usually bright yellow and black and eat many kinds of plants and insects.
Owl
Spiders and praying mantis do.
there isn't an insect who feeds on fishes.
yes i think that is how it goes in a ecological pyramid.
The peach-potato aphid eats the leaves of trees like the peach tree. This insect can cause a lot of damage to trees as well as crops.
Owl
a lizardfly
grasshopper
The nightingale eats spiders and ants.
A xylophagous insect is one that eats wood. A phyllophagous insect is one that eats plants.
Termites