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Hemimetabolous


[R] Refers to insects showing gradual change from moult to moult, the nymph transforming directly into the adult without a pupal stage, and wing pads developing externally.
Some insects (e.g. the Aleyrodidae and the Psyllidae) exhibit a pupa-like instar.
The nymphs and adults of hemimetabolous insects are usually similar in shape and habits.
Perhaps no concept in entomology has resulted in more polarization of thought than that of categorizing development into types. One classification includes insects that have immatures with external wing pads, the Exopterygota, and species that have internal wing pads as larvae, the Endopterygota. Another classification agrees with the previous demarcations but substitutes Hemimetabola for Exopterygota and Holometabola for Endopterygota. Another view separates the Exopterygota into Paurometabola (for those whose immatures develop terrestrially) or Hemimetabola (whose immatures inhabit water) and retains the Endopterygota as a single unit, the Holometabola. However, the terms Hemimetabola and Holometabola seem to have a more worldwide usage.
Major hemimetabolous insects important in plant protection include the Orthoptera, the Thysanoptera, the Heteroptera and the Homoptera.


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