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|Female Gasteruption jaculator(Linnaeus, 1758)of the family of the Gasteruptionidae.|
Larvae feed on grubs of solitary bees.
Biology and Host Relationships
Early records indicated that twig-nesting species of solitary bees (e.g. Ceratina, Heriades and Hylaeus) were the only hosts for Gasteruption (Höppner 1904; Rau 1928). More recent and extensive records indicate that a much wider range of solitary bees and wasps act as hosts for this genus including the Anthophoridae, Colletidae, Megachilidae, Sphecidae, and Vespidae (Masarinae) (Jennings and Austin 2004). Available data also suggest that individual Gasteruption species vary from being polyphagous to having a more restricted host range. For example, the European species G. assectator F. and G. jaculator (L.), apparently have a wide host range (Colletidae, Megachilidae, Sphecidae and Vespidae), while others such as G. caudatum Szépligeti and G. freyi (Tournier) are recorded as parasitising only Megachilidae and Colletidae, respectively. However, these data are based on a restricted number of records and should therefore be treated with caution.
Upon detecting a potential host nest, the female wasp will hover around and antennate on the entrance (Morley 1916). She will then repeatedly settle and thrust the full length of the ovipositor into the nest while the valves remain at right angles to the trunk. In the case of an already sealed nest, the wasp pierces it by pushing without any drilling action. Gasteruptiids do not have grooves on the hind coxae to guide the ovipositor like their probable sister family, Aulacidae.
Different species of Gasteruption deposit their eggs in proximity to the host egg, with the exact positioning depending on the species (Malyshev 1964, 1966). Some species are ectoparasitic, in that they lay their eggs on the egg of the host bee or wasp. Other species lay their eggs on the store of honey just in front of the host egg, on the wall of the cell in front of the food store, or on the outer surface of the cell lining. Höppner (1904) reported that G. assectator is ectoparasitic on Hylaeus spp. and actually oviposits onto the mature host larva.
There are considerable differences among species in the exact method of parasitism, with the larvae of some species consuming the host egg and others consuming the host larvae. For example, shortly after hatching, the larvae of G. caudatum and G. pyrenaicus consume the host egg (Malyshev 1966). The second instar larvae of these two species then feed on the food store of the host bee. In some cases the larva completes its development by consuming the food store in more than one cell: if the partitions are weak or brittle, the larva may invade surrounding cells where it consumes both bee larvae and food stores. In comparison, the larva of G. assectator consumes a mature Hylaeus larva upon eclosion (Höppner 1904); it then invades a second cell and consumes that larva also.
Information regarding pupation in Gasteruption is very scarce. The larva of G. robustum pupates at the end of the tunnel of the host bee where it seals itself off with a tough partition constructed from an anal excretion (Whatmough 1974). Gasteruption caffrarium pupates inside two cells of Hylaeus (Skaife 1953), while G. assectator pupates in a cocoon within the cell of its host (Crosskey 1951). Pupation within the host cell has also been observed in Australia for several Gasteruption spp. (Jennings and Austin, unpublished).
Adult Feeding and Phenology
Gasteruption have elongate glossae (Fig. 1), typical of nectar feeding wasps. The galeae are flattened and foliaceous with a fringe of stout comb-like setae on the inner margin (the galeal pecten), the fused glossae (the glossa sensu Crosskey) are well developed, and paraglossae reduced (Crosskey 1951). Examination of the mouthparts of a range of Gasteruption spp. revealed pollen on approximately one-third of individuals, although the load varied considerably with species (Jennings and Austin unpublished). Given the range of plants visited that produce both pollen and nectar, it is likely that at least some Gasteruption feed on both nectar and pollen (Jennings and Austin 2004).
Although data for most regions are either scarce or non-existent, adult Gasteruption have been recorded as visiting a wide range of flowers from many species and families. Apiaceae(like on this picture; In Dutch it is called; Schermbloemigen!) appear to be favoured by Gasteruption in the Palaearctic region and Myrtaceae in the Australian region. This family is dominant in the Australian flora with over 1500 species and it is therefore not surprising that Gasteruption have been widely recorded as visiting this plant group. Myrtaceae visited by Gasteruption include Angophora, Eucalyptus, Leptospermum, Lophostemon, and Melaleuca (Jennings and Austin 2004). These genera produce both pollen and nectar in large quantities and are visited by many groups of insects. Other plants visited such as Schinus (Anacardiaceae), Banksia and Grevillea (Proteaceae), and Atalya (Sapindaceae) also produce both pollen and nectar.
Gasteruption caffrarium is multivoltine with two or three generations occurring each year in southern Africa (Skaife 1953). Collection data for other Gasteruption indicate that in North America, G. assectator are collected between late April to early Oct., with the peak in late May, whereas G. pattersonae Melander & Brues are collected from late April to mid September (Townes 1950).
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