Wing Folding in the Hymenoptera

Longitudinal folding (plaiting) of forewings at rest has arisen independently in Vespidae, Colletidae, Gasteruptiidae, Figitidae, Leucospidae, and Pompilidae. In the first five families the plaiting fold is similar in position, but in the last family its position is different. A type of wing folding unique to the eucoilid genus Kleidotoma—wrapping flexure—is described. In all cases, evolution of wing folding is associated with modifications of wing morphology (most commonly, regions of vein flexibility termed alar fenestrae). The mechanism of wing folding in the family Vespidae includes a "click" mechanism at the intersection of the plaiting fold and the claval furrow in the region of vein cu-v; it has only two stable positions, inverted and everted, giving the vespid forewing only two stable configurations, fully unfolded and fully folded, respectively. Folding involves movement of the third axillary sclerite and vannal vein in addition to hind wing movements; unfolding is probably partly the result of vannad movement of the hind wing as the wasp prepares to fly but can occur even if a hind wing has been removed. Teneral Polistes wasps lack plaiting folds for about 36 h after eclosion. Removal of either a teneral hind wing or the hamuli of a teneral hind wing often permanently prevents folding of the ipsilateral forewing, indicating that the hind wing hamuli are important in fold development. Folding of vespid wings may help to protect them from damage in close quarters. Folding of colletid, leucospid, and pompilid wings may be mimetic of vespids, an idea supported by the fact that diverse groups of wasplike Hymenoptera, Diptera, and Lepidoptera have forewings with a darkly pigmented leading half that appears to enhance their resemblance to Vespidae. Folding in Figitinae and Kleidotoma may allow less hindered movement through moist dung and decaying plant and fungal material, the habitats of their fly hosts.