Immature developing (L1 and L2) and infective (L3) stages of nematode larvae, e.g. filariasis, hookworm etc.... In filariasis, after an infective blood meal, microfilariae exsheath, penetrate the stomach wall and pass into the haematocoele, from where they migrate to the thoracic muscles of the mosquito. In the thorax, the small larvae become more or less inactive, grow shorter but considerably fatter and develop, after 2 days, into “sausageshaped” forms (L1). They undergo two (2) moults and the resultant third stage larvae (L3) become active. This is the infective stage and is formed some 10 days or more after the microfilariae have been ingested with a blood meal.
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