ABSTRACT
In the preceding lecture I called attention to the fact that the Terebrant, or parasitic and the Aculeate, or stinging Hymenoptera are so closely related that most modern authors unite them in a single sub-order, the Clistogastra, and that the Aculeates are usually supposed to be derived from Terebrant ancestors though others would derive both groups from common or closely allied hypothetical forbears among primitive Phytophaga. Whichever view we accept and notwithstanding the fact that the Terebrants use the ovipositor for egg-laying whereas it is converted into a sting in the Aculeates and, with the exception of the Sapygidæ, Chrysididæ and Dryinidæ, is not employed in oviposition, we must admit that the Terebrants have already developed certain characteristics which occur with more or less modification and elaboration among the higher Aculeates. Among these peculiarities attention may be called to the following:
Even among Terebrants there exists a sporadic tendency to a development of polymorphism in one or both of the sexes. Thus in the Braconid Sycosoter lavagnei, according to Lichtenstein and Picard (1917) and Picard (1919), there are two forms of each sex, one winged, the other apterous. Two forms of females are also well-known in certain Chalcidids, e.g., in Harmolita (Webster and Reeves, 1909) and Cynipids, and among the fig-insects of the Chalcidoid tribe Idarnini (Phylotrypesis) Grandi (1921, 1923) has revealed the existence of a peculiar polymorphism very much like that of certain worker ants, though confined to the male sex. In Pezomachus flavocinctus Strickland (1912) has described a peculiar polymorphism of the male, which may be winged, subapterous or apterous. These cases of the loss of wings in one or both sexes and especially in the female and considerable variation in the size of the head and mandibles in individuals of one of the sexes among Terebrants somewhat diminish our surprise at their more frequent occurrence among certain groups of Aculeates.
In certain Terebrants the ovipositor may act like the Aculeate sting and introduce into the prey a poison which induces at least a temporary paralysis of the musculature. This has been observed by Silvestri (1907) in the Chalcidid Elasmus flabellatus, which completely paralyses the larva of the Tineid Prays oleellus in which it oviposits. Doten (1911) found that Microbracon juglandis completely paralyses the caterpillars of Ephestia kühniella, so that the latter remain fresh for from two to four weeks, and Picard (1919) has observed a similar but feebler paralysis of the larvæ of Hypoborus ficus by Sycosoter lavagnei. The paralysis of blowfly larvæ by Alysia manducator has been carefully studied by Altson (1920) and Myers (1927).
It is well-known that some Terebrants lay their eggs within the body while others lay them on the surface of the prey, but that the latter method alone is employed by the Aculeates, with the exception of the Dryinidæ. Several authors and more recently Picard (1919) have called attention to the fact that external oviposition is employed among the Terebrants when the prey is concealed in a plant or earthen cavity, or in a cocoon or puparium and that internal oviposition is the rule when the host is exposed, or free-living. Among the exceptions we may mention Polysphincta, which parasitises spiders (Lichtenstein and Rabaud, 1922) and the Chalcid Schizonotus sieboldii which, according to Cushman (1917) lays its eggs on the exposed pupæ of a Chrysomelid beetle (Melasoma interruptum). The same author calls attention to the Eulophid Euplectrus comstocki which oviposits on the cotton worm. Silvestri (1911) has described this habit also in the European Euplectrus bicolor which parasitises the caterpillars of Plusia gamma and Mamestra brassicæ. The general rule of oviposition on the outside of the prey when it happens to be in a cavity applies also to the Aculeata, but the Rhopalosomatidæ and some Pompilidæ are known to attach their eggs to free-living insects.
A phenomenon frequently noticed in Aculeates that paralyse their prey (Figs. 13 and 14) is their malaxation or feeding on portions of it. This is very natural because the adult Aculeate is then merely continuing to eat portions of an insect of the kind on which it was reared as a larva. The same tendency is apparent in many Terebrants but in them usually takes the form of feeding on the juices exuding from punctures made by the ovipositor in the egg, larva, pupa, or adult of the host species and immediately after oviposition or after the ovipositor has been used merely as a food-procuring instrument. This singular behaviour was first observed by Marchal (1905, 1909) in Tetrastichus xanthomelænæ which oviposits in the eggs of the elm-leaf beetle (Galerucella xanthomelæna) and in Aphelinus mytilaspidis, which oviposits in a scale (Aspidiotus ostreœformis). It has also been observed by several American entomologists in Tetrastichus asparagi which oviposits in the eggs of the asparagus-beetle (Crioceris asparagi); by Saunders in Aphelinus fuscipennis, which parasitises the scale Aspidiotus rapax (Howard 1908); by Silvestri (1910) in Tetrastichus xanthomelænæ; by Doton (1911) in Pteromalus puparum and a species of Meraporus, as parasites of the pupæ of the cabbage-butterfly (Pieris rapæ) and in Microbracon juglandis as a parasite of the meal-moth (Esphestia kühniella); by Roubaud (1917) in Nasonia brevicornis which oviposits in the puparia of Muscids; by Lichtenstein (1921) in the Chalcid Habrocytus cionicida which lays its eggs in the pupæ of a weevil (Cionus thapsi); by Trouvelot (1921) in the Braconid Habrobracon johansseni, by Whiting (1921b) in H. brevicornis which attacks the mealworm; by Caffrey (1921) in Anastatus semiflavidus, an egg-parasite of the moth Hermileuca oliviæ; by Balfour Browne (1922) and Picard (1923) in the Chalcid Melittobia acasta which lays its eggs on the larvæ and pupæ of a great variety of Hymenoptera, Diptera and Coleoptera, and by Voukassovitch (1924) in the Ichneumonid Dicælotus erythrostoma, a parasite of Polychrosis botrana. The most singular of these cases is the Habrocytus described by Lichtenstein, because the Chalcid runs its ovipositor through the cocoon of the beetle and the space between the cocoon and the pupa and into the latter. It leaves the organ in this position for half an hour while a secretion hardens around it and forms a delicate tube through which the parasite sucks the blood of the prey as soon as the ovipositor is withdrawn. It will be seen that in all the cases cited the mandibles are not used in feeding because the prey is too large and too tough-skinned, whereas in the larger and more powerful Aculeata the mandibles may be readily employed for a similar purpose. There are, however, small Aculeates (Bethylidæ) which, as I shall show in the sequel, use the sting like the Terebrantia for securing food. Sphex procerus carrying caterpillar of sphinx moth to her burrow. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315624860/b7db499d-021e-4429-8d47-d72d25357df1/content/fig13_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Photograph by Prof. Carl Hartman.) (See p. 52.) Burrow of Sphex procerus in section, showing filling of débris in the tunnel and the paralyzed Sphinx moth caterpillar in the cell, with the egg glued to its side. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315624860/b7db499d-021e-4429-8d47-d72d25357df1/content/fig14_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Photograph by Prof. Carl Hartman.) (See p. 52.)
Perhaps we may detect the germs of a feeble sociability in those Terebrants which develop in numbers in the same host and when mature, pupate in compact masses of cocoons. In one genus of Chalcididæ, Cratotechus, or Comedo (Fig. 11), as it is now called (Howard 1891), the pupæ are naked and are attached to a leaf side by side in a regular ellipse enclosing some of the individuals, an arrangement which seems to presuppose a peculiar “Fühlung”, to use a German expression, among the larvæ. It must be admitted, however, that sociability is much less pronounced among larval Terebrants than among the more ancient and primitive Phytophaga and that there are many instances of internecine destruction among the young larvæ when the prey is too small to nourish more than a single parasite.
