Evolution of Suction Feeding

The first fluid-feeding insects employed a lapping or sponging mechanism to imbibe their liquid meals. This modality, which uses capillary forces for fluid uptake, is widespread among insects, including those that specifically visit plants to consume floral nectars [27]. The elongation of mouthparts is derived and enables insects to develop a pressure gradient along the food canal, allowing them to consume nectar from the concealed nectaries found in long, tubular corollas (Figure 9.1). This type of proboscis, termed a "concealed nectar extraction apparatus" by Jervis [28], often matches or exceeds the body length in holometabolous insects (Endopterygota) and other nectar feeders (Table 9.1 and Figure 9.1). At 280 mm, a tropical sphingid holds the record for mouthpart length in absolute terms [29]. Relative to body length, however, record holders are South African nemestrinid flies (Figure 9.1C) whose proboscides may be over four times the length of their bodies [15]. A number of disparate evolutionary pathways have preceded the development of these long, suctorial mouthparts in various taxa (Table 9.2).

FIGURE 9.1 (A) Hawkmoth Xanthopan (Sphingidae) approaching the long-spurred blossom of an Angraecum orchid; proboscis length approximately 220 mm (photo with permission of L.T. Wasserthal). (B) Orchid bee, Eulaema meriana, departing from a Calathea inflorescence (photo with permission of G. Dimijian). (C) Long-proboscid fly Moegistorhynchus longirostris (Nemestrinidae) at a flower of Ixia (photo with permission of S. Johnson).

FIGURE 9.1 (A) Hawkmoth Xanthopan (Sphingidae) approaching the long-spurred blossom of an Angraecum orchid; proboscis length approximately 220 mm (photo with permission of L.T. Wasserthal). (B) Orchid bee, Eulaema meriana, departing from a Calathea inflorescence (photo with permission of G. Dimijian). (C) Long-proboscid fly Moegistorhynchus longirostris (Nemestrinidae) at a flower of Ixia (photo with permission of S. Johnson).

Many taxa within Hymenoptera have evolved elongate mouthparts in the context of nectar feeding [28,30]. Many of these feed on nectar using a lapping and sucking mode, but the Euglossini (orchid bees) and long-tongued Masarinae (pollen wasps) have shifted to pure suction feeding [31,32]. In other cases, a suctorial mode of feeding is suggested from the length and general composition of the mouthparts (e.g., some species of Tenthredinidae, Eumenidae, and Sphecidae [27,28,30]).

Suctorial nectar feeding via an elongate proboscis has arisen multiple times in Diptera [33]. Suction feeding in hoverflies (Syrphidae) [34] and beeflies (Bombyli-idae) [19,35] likely evolved from unspecialized flower-visiting ancestors employing a sponging feeding mode on floral and extrafloral nectar and pollen. Specialized nectar feeding in the Culicidae and Tabanidae evolved from hematophagous ancestors [36]. While both sexes of the tropical culicid genus Toxorhychites shifted entirely to floral nectar, female horseflies in the genus Corizoneura are equipped with both a short proboscis (10 mm) for piercing and sucking blood, and a long proboscis (50 mm) for nectar feeding [37]. In addition, nectar-feeding flies belonging to the Empitidae (dance flies) are derived from predatory insect feeders [36].

Even though generalized feeding on petals, nectar, and pollen is frequent among adult beetles, only two taxa of blister beetles (Meloidae) have independently shifted to specialized nectar feeding via an elongate proboscis [36,38].

Ancestors of butterflies and moths fed on nonfloral plant fluids with a simply formed, coilable proboscis. The proboscides of all nectar-feeding Lepidoptera exhibit the same set of derived features, suggesting that nectar feeding evolved only once in a taxon of glossatan Lepidoptera known as the Eulepidoptera [39,40].

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