The glasshouse whitefly is a major pest of protected crops, occurring on aubergine, cucumber, climbing French bean, melon, sweet pepper, tomato and various ornamentals. Whilst conditions remain favourable, the insects may also survive on various weeds out of doors. Infested plants show poor growth and the foliage may become discoloured; when attacks are heavy, leaves wilt and die, and crop yields will be depressed. Attacked plants become coated in honeydew, upon which sooty moulds soon develop; vegetables such as cucumbers and tomatoes often need to be washed before they can be marketed.
Whitefly infestations occur mainly on the underside of leaves, eggs being typically deposited in circular groups on smooth leaves but more scattered on hairy ones. Adults are particularly abundant on the uppermost parts of plants, and readily take to the wing when disturbed. They breed continuously whilst conditions remain favourable, each female being capable of depositing 200 or more eggs over a 6-week period; reproduction is normally parthenogenetic. At normal glasshouse temperatures, eggs hatch in about a week to 9 days. The nymphs (the so-called 'scales') at first wander over the foliage but soon become sedentary on the underside of the leaves, where they continue their development. They pass through three instars before entering a brief, non-feeding, pseudo-pupal stage. Development from egg to adult usually takes less than a month and populations in glasshouses can build up very rapidly, with a succession of overlapping generations occurring throughout the summer.
Adult 1mm long, pale yellow to whitish; wings white, and held relatively flat when in repose (cf. tobacco whitefly, Bemisia tabaci, above). Egg 0.2mm long, yellowish, broadly conical, becoming blackish after a few days. Nymph translucent to pale green, oval, flat, scale-like. Pseudo-pupa oval, whitish,7 with relatively short marginal waxen processes and several pairs of long waxen tubes dorsally.
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