Organic Evolution in terms of the Implicate and Explicate Orders.


Hymenoptera (wasps, bees, ants) (Sequel)

The evolutionary diversification in the Order Hymenoptera in terms of Strategies (Sequel).

Immediately-parasitic (orthoparasitic) phase

The delay [= laying eggs at a later time in the season] of laying eggs into the galls of archaic saw-flies had different consequences for those terebrant-inquilines in which, in contrast to the Trigonalidae, did not take place a degeneration of the ovipositor, but a progressive development of it. The possession of a fairly developed borer provided these primitive terebrants with the possibility to lay their eggs onto more or less fully-grown larvae of saw-flies that freely lie in the cavity of galls caused by them. After having destroyed [and consumed] the larva of the saw-fly, the ectoparasitic larva of the inquiline first could continue its [evolutionarily] original feeding on the walls of the gall. Similar cases of mixed feeding, although seldom and in somewhat different conditions, is observed also today. Thus, according to a statement of NIELSEN (1915), noted earlier,  Eurytoma  salicis  Thoms.,  after having first destroyed [and consumed] the larva of the saw-fly  Euura (Cryptocampus)  angustus  Htg.,  which lives in a gall on green shoots of willow, continues feeding on the walls of the gall. In the same way, as was reported,  Eurytoma  inquilinum  R.-Kor.  attacks the larva of  Isosoma  rossicum  R.-Kor.  and sucks it out, and then gnaws on the walls of its gall. And also  Syntomaspis  eurytomae  Puz.-Mal.  first destroys the larva of the  Eurytoma  and then feeds on the remains of the kernel of the plum.
Subsequently, when laying of eggs onto completely-grown larvae of the preys [evolutionarily] began, the supplementary feeding on the walls of the galls lost its significance to the terebrants. Now their instinct began to specialize on the preys themselves, already independently of the fact whether they produce galls or whether they simply live inside plants. To the attack of the original terebrants of the present group became subjected here endophytic larvae of various insects, living in similar ecological conditions, first of all, one must assume, larvae of stem saw-flies and horn-tails, and then also beetles (especially Buprestidae and Cerambicidae) living inside plants.
It is clear that in the indicated conditions in which preys are infected, preys, that live not far beneath the surface of stems, leaves, and the like, to the terebrants there was no need for whatever special morphological adaptations. But subsequently, in search for new preys a part of the terebrants began to infect preys that live far beneath the surface, in the thickness of wood. See next Figure.

Figure 1 :  The ichneumonoid terebrant  Thalessa  lunator  F.  drives its ovipositor into the thickness of wood, infected with a larva of a horn-tail.
(After RILEY, 1888, in MALYSHEV, 1966)

In these special conditions, in order to directly infect the prey-larva, a corresponding development of the ovipositor was demanded. In some such terebrants it indeed enjoyed an extraordinary development, eventually reaching a maximal size. Thus, for instance, in one representative of the Pimplinae from Peru it reaches a length of 15 cm, being 7.5 times longer than the [rest of the] body of this terebrant, and also one braconid from Colombia (Iphiaulax  sp.) possesses an ovipositor 14 times longer than its body. It is not known for what exactly, and in what way, such an extraordinary device is used. The author already earlier had the opportunity to tell that such a specialization of the organism, directed to be able to reach deeply concealed host-larvae, here has arrived at its very limit, and has, we must think, led these terebrants to a dead end [meaning that, because retrogade evolution of complete whole structures is (probably rightly) assumed to be impossible ('forbidden'), from the state the terebrant is in now, no subsequent (evolutionary) derivation is possible anymore]. After the object to which egg-laying was directed generally had become the endophytically living prey, still one step forward had to be made :  this object, at least to terebrants in which the ovipositor has not undergone a strong development, became the very prey, [having become so] independently of the nature of the place where it lives. And as soon as the instinct of the insect had freed itself from the necessity of a narrow (limited) selection of preys, concealed in the plant substrate, it began to specialize on preys that live out in the open, unconcealed -- on the surface of shoots, leaves, and the like. In the beginning, one might think, these were preys that were still closely related to those that lived in plants, such as, for instance, larvae of saw-flies living [now] in the open. Subsequently in the overwhelming majority of forms this connection was completely lost, and now also those preys became to be subjected to attacks that were in no way related to the original forms anymore, such as caterpillars of butterflies and even their pupae.
In connection with this, the behavioral patterns of terebrant-Tryphon's (from the Ichneumonidae), possessing a short or even concealed ovipositor, are interesting. They lay their eggs under the skin of larvae of saw-flies (behind the head) living in the open, at the expense of which they ectoparasitically develop. Also on [not in] larvae of saw-flies develop ichneumonoid terebrants of the subfamily Lisiognathinae. As a wonderful illustration of this kind of phenomenon may serve the observations of  SHEVYREV (1912), which will be presented a little later, on the ectoparasitic behavior of the ichneumonoid  Paniscus  ocellaris  Toms.,  which attaches its eggs onto the skin of a caterpillar, especially of night-owls (Noctuidae), and sometomes also of other butterflies.
The rarity of this kind of behavior indicates that it is in one or another way conncted with special difficulties. And these should, from our point of view here presented, indeed be expected. As a matter of fact the maternal instinct of the terebrant now did not so much specialize with respect to the very place where the prey lives (gall, stalk), but to finding the prey itself. And the latter lives in a different, open place. With this the historically developing delicate larva of the parasite had placed itself, we might say, in abnormal conditions :  earlier having been adapted to a life in an environment well-isolated from external unfavorable influences, it now had to live out in the open, outside the host, and not possessing its own protective integument. While in the adult terebrants the corresponding transformation of instincts did not demand great organic changes, and could therefore proceed easy and fast, for the larvae of them this meant the necessity of deep-seated organic adaptations to the new conditions. It is clear that here the larva could not catch up with the mother [did not possess such adequate an adaptation to living in the open]. Such situations almost in their pure form do still exist, but have become rare phenomena, because Nature soon found various ways out of the created difficulty. Subsequently did change, as one may think, chiefly the instincts of the adults, although the look [external morphology] and behavior of the larvae also changed. The essential adaptation here was the selection by the female terebrants of fully-grown host-larvae, having already concluded their feeding. As a result the external [outside the very host] life of the delicate parasitic larva on the body of the prey took already place under the protection of a cocoon, puparium, or generally, a pupal cradle of the host, as it is observed, for example, in  Tryphon  semirufus  Uch.,  Paniscus  geminatus  Say.,  and others.
Other terebrants had, for laying their eggs, to return to concealed preys. Some of them ended up in other, sometimes totally unusual conditions, and began, for instance, to look for larvae living under water. Thus, the female of the caddis-fly terebrant  Agriotypus  armatus  Walk.  (of the family Agriotypidae, which is represented only by the mentioned genus), without being able to swim, descends under the water while holding itself on to aquatic plants and other submerged objects, and in this way reaches cases [= 'houses' made from sand-grains, plant material, or small shells] of caddis-fly larvae (Trichoptera). For the wasp see next Figure.

Figure 2 :    Agriotypus  armatus  Walk.,  female.  Family  Agriotypidae.
(After R. and H. Heymons, 1909, from WESENBERG-LUND, 1943)

[For this and other aquatic terebrants, see Part XXXVI of the present Series, "Extract from Wesenberg-Lund" ]
If in the case there is a caddis-fly larva, then, disturbed by the ovipositor of the terebrant, it makes a forward move. Then the terebrant leaves it alone and departs, searching for such a (caddis-fly) case in which there is a pupa or prepupa which cannot [as most of these] move, and lays an egg in this case at it. In executing this operation the female  Agriotypus  can stay under water for a period of about four hours, an then stops holding itself on submerged objects, floats to the surface without making any swimming movements. The  Agriotypus-larva feeds on the caddis-fly larva in the form of an ectoparasite, although it is possible that in its first instar it lives inside it. Having eaten the whole body of the prey, the terebrant larva makes a cocoon, lying from inside against the walls of the case, whereby it provides the cocoon with a special appendage, that projects from the case as a narrow band of up to 5 cm. Probably this appendage serves respiration of the parasite, because when it is removed the terebrant larva dies. See next Figure.

Figure 3 :  Case of  Silo,  paralyzed by  Agriotypus  armatus.
(After Brocher, 1913, from WESENBERG-LUND, 1943)

As an indicative example of laying the eggs onto (or next to) precisely that larval state of the host at the expense of which the terebrant also develops [that is, no delayed development] may serve the behavior of the peculiar chalcid  Leucospis.  Here before us we have a case of a terebrant, [evolutionarily] earlier having been an egg-eater, but now having already lost the connection with the egg stage of the host, that became a solitary parasite of a large prey, still carrying the characteristic traces of structural reduction of the egg-eaters. According to the substantial investigations of FABRE (1855), the female  Leucospis  (L.  gigas  F.) with the ovipositor bores through the mineral walls of a cell of a mason bee  (Chalicodoma  muraria  F.  (next Figure) and  Ch.  pyrenaica  Lep.)  and suspends its egg next to the fully-grown  Chalicodoma-larva that already had twined round a cocoon. Having emerged from the egg, the mobile  Leucospis-larva, looking like primitive planidium, restlessly crawls around and destroys the other eggs of its relatives in the case when they happen to be in the same cocoon. Having completed all this, it moults and transforms into the usual worm-like terebrant larva, and then starts to swallow the prey.

Figure 4 :   Chalicodoma  muraria .  Apoidea (bees).
(After CHINERY, in Elseviers Insektengids voor West-Europa, 1983)

May be, to this phase of development we might, as to their behavior, also reckon the mysterious Pelecinidae, which will be dealt with later.

A part of the terebrants, while emerging from the egg, laid onto a prey that has concluded its development, was able to penetrate under the host's muscular skin and, having adapted there to the new physiological conditions, avoided in this way the direct influence of the external environment. Subsequently, such terebrant species began to lay eggs directly into the body of the prey, where also they had almost all of their [individual] development (until pupation) or all of their development.
Earlier it was already stated that the endoparasitism of the terebrants had originated in different phases of their evolution -- in the egg-eating (endo-oophagous), in the delayed-parasitic, and in the passively-parasitic phase. Now we see yet another way of origin of endoparasites -- in the present phase, that is, in the orthoparasitic phase. To this origin [i.e. still standing amidst the process of creation of the endoparasitic way of life in the relevant group] belongs, for example, that particular case in which the terebrant  Monodontomerus  aereus  Walk.,  which usually develops as an ectoparasite in ripe puparia of flies [a puparium is the last larval skin, hardened into some sort of barrel, in which the pupa of the fly rests], sometimes lays its eggs into not yet ripened puparia with the larval skin not yet separated from the pupa [in content and grammar this sentence is not clear in the original text. I have made the best of it.] ["the larval skin not yet separated from the pupa" implies that the parasite, finding itself on the developing pupa, is in this condition still an endoparasite, because it is under the (last) larval skin, which has still not hardened into a puparium, and therefore still being a true larval skin]. In such a case only a few chalcid larvae, having emerged in the cavity of host's body, and having consequently become endoparasites, can manage to attain maturity and emerge as an (winged) adult insect.
But it is problematic to suppose that somewhere in the evolutionary path of the terebrant-endoparasites there was still (as in the ectoparasites) a stage of mixed feeding. When this would be the case than one must hold that the, while inside the prey, not yet sufficiently developed terebrant larva, upon exiting that prey, would feed on the walls of the gall, that is, from an endoparasite would originate a phytophag. This is already very unlikely. And it follows that the immediately-parasitic line of evolution of endoparasitic terebrants was realized in a different way as was the case in the ectoparasites.
From what has been expounded follows that many terebrants of the group presently under discussion, especially of the ichneumonoids and braconoids, did not in their evolutionary history go through the egg-eating (oophagous) phase at all, and were able therefore to preserve their normal growth. In different cases, moreover, of solitary parasitism on large preys, the orthoparasitic terebrants were not only in the position to restore their sizes (as in  Leucospis), but even to attain maximal sizes within all remaining terebrants, such as [such large terebrants as]  Rhyssa  and  Thalessa.
Thus, development at the expense of the more or less fully-grown larval, prepupal, or pupal stage of the hosts, on which or in which these terebrants lay their eggs, is the characteristic feature of the immediately-parasitic, or orthoparasitic phase.

With all this we conclude our exposition of the Immediately-parasitic (orthoparasitic) Phase of hymenopterous evolution.
In the next document we will deal with the Imaginally-parasitic Phase.

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