As with scale insects, whiteflies develop from eggs to adults through incomplete metamorphosis. Once eggs hatch, the immature whiteflies increase in size by passing through four nymph stages, called "instars." Like armored scales, only the 1st instar nymphs are mobile, so they are commonly called "crawlers." The 2nd, 3rd, and 4th instar nymphs are immobile; these "settled" nymphs remain firmly attached their host plants as they sip plant sap.
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