http://mp.weixin.qq.com/s/YsUg3D5rmKKKUN-5oeoeyg
来自英文巴士
00:2903:43
NB: This may not be a word-for-word transcript.
A Simple Way to Tell Insects Apart
Anika Hazra
A whip-like straw. Powerful, crushing blades. A pointed, piercing tube. There are nearly a million known insect species in the world, but most have one of just five common types of mouthparts. And that’s extremely useful to scientists because when they encounter an unfamiliar insect in the wild, they can learn a lot about it just by examining how it eats.
Scientific classification, or taxonomy, is used to organize all living things into seven levels: kingdom, phylum, class, order, family, genus, and species.
The features of an insect’s mouthparts can help identify which order it belongs to, while also providing clues about how it evolved and what it feeds on. The chewing mouthpart is the most common. It’s also the most primitive – all other mouthparts are thought to have started out looking like this one before evolving into something different. It features a pair of jaws called mandibles with toothed inner edges that cut up and crush solid foods, like leaves or other insects. You can find this mouthpart on ants from the Hymenoptera order, grasshoppers and crickets of the Orthoptera order, dragonflies of the Odonata order, and beetles of the Coleoptera order.
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The piercing-sucking mouthpart consists of a long, tube-like structure called a beak. This beak can pierce plant or animal tissue to suck up liquids like sap or blood. It can also secrete saliva with digestive enzymes that liquefy food for easier sucking. Insects in the Hemiptera order have piercing-sucking mouthparts and include bed bugs, cicadas, aphids, and leafhoppers.
The siphoning mouthpart, a friendlier version of the piercing and sucking beak, also consists of a long, tube-like structure called a proboscis that works like a straw to suck up nectar from flowers. Insects of the Lepidoptera order – butterflies and moths – keep their proboscises rolled up tightly beneath their heads when they’re not feeding and unfurl them when they come across some sweet nectar.
With the sponging mouthpart, there’s yet another tube, this time ending in two spongy lobes that contain many finer tubes called pseudotracheae. The pseudotracheae secrete enzyme-filled saliva and soak up fluids and dissolved foods by capillary action. House flies, fruit flies, and the other non-biting members of the Diptera order are the only insects that use this technique. But, there’s a catch. Biting flies within Diptera, like mosquitoes, horse flies, and deer flies, have a piercing-sucking mouthpart instead of the sponging mouthpart.
And finally, the chewing-lapping mouthpart is a combination of mandibles and a proboscis with a tongue-like structure at its tip for lapping up nectar. On this type of mouthpart, the mandibles themselves are not actually used for eating. For bees and wasps, members of the Hymenoptera order, they serve instead as tools for pollen-collecting and wax-molding.
Of course, in nature, there are always exceptions to the rules. The juvenile stages of some insects, for example, have completely different kinds of mouths than their adult versions, like caterpillars, which use chewing mouthparts to devour leaves before metamorphosing into butterflies and moths with siphoning mouthparts.
Still, mouthpart identification can, for the most part, help scientists – and you – categorize insects. So why not break out a magnifying lens and learn a little more about who’s nibbling your vegetable garden, biting your arm, or just flying by your ear.
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