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Calliphoridae c Other Diptera. Trogidae e Other Coleoptera. BoxKampala, Uganda. Greathead the insect enemies of Amdoidea Orthoptera I. There is thus a great body of literature on natural enemies and much of it was summarised by Uvarov in a chapter in his Locusts and Grassbpers. Since then there have been various reviews on the habits and importance of some of the groups of entomophagom insects e.
Balduf,on entomophagous Coleoptera ; Clausen published an extremely useful survey of all entomophagous insects, but could not deal in detail with all the natural enemies of acridoid insects in so comprehensive a work.
It has therefore been thought worth while to prepare a review, chiefly for the aid of field workers, of the life histories and siglllficance of the more important group of insect enemies of Acridoidea. In most cases it has been possible only to give a generalised account of each family or genus, mentioning the chief sources of information, and thus avoiding repetitive references and conflicting details and opinions.
To supplement the general text, a catalogue of all the insect enemies, with references, has been provided. This list is as complete as possible and the author has, he hopes, included all the more useful recent works, especially those giving more than mere lists of species. In each section brief notes have been given on the characteristics of the damage done by, or appearance of, the entomophagous stage, and reference has been made to any comprehensive taxonomic works known to the author.
More general works, which will be found useful for identifying insect larvae but which have not been mentioned in the text, are: Hennig, ; Boving and Craighead, ; Rymer Roberts, Drawings of typical stages and characters of the natural enemies have been in- cluded where possible.
It is not possible to give an outline of the quantitative methods used in studying the effects of natural enemies, as these vary widely according to the size and type of population and the conditions under which they are being studied.
A REVIEW OF THE INSECT ENEMIES OF ACRIDOIDEA (ORTHOPTERA) – [PDF Document]
Recent works that have discussed the quantitative effect of insect enemies and have related them to total mortality are Richards and Waloff on British grasshoppers; Dempster on the Moroccan Locust in Cyprus; Stower, Popov and Greathead on a Desert Locust egg-field in Eritrea; Stower and Greathead in pepara.
This is not always an easy matter, as many species diapause in one of the earlier stages and are easily killed by handling or abrasion by soil particles. The Bombyliidae, Nemestrinidae and allied families, and the majority of the Coleoptera concerned, all diapause in the final larval instar and it is very diilkult to induce pupation.
The tropical species, and possibly some of the temperate ones, will only pupate if the soil in which they are kept is alternately mordan and allowed to dry out. This is most easily achieved by using a jar or specimen tube covered with gauze to prevent undue humidity in the container leading to the growth of fungi.
All these diapausing larvae are very sensitive to abrasion of the cuticle by soil particles and are best not transported. If transportation is necessary, the larvae should be placed D. Greathead on the insect enemies of Acridoidea Orthoptera in cavities made in firmly packed damp soil in specimen tubes plugged with cotton wool to obviate abrasion. Calypterate larvae can be placed in ruropea specimen tubes with a piece of slightly damp blotting paper or cellulose wool to prevent desiccation and give purchase to the emerging adult.
The examination, for natural enemies, of acridoid egg-pods of species which lack a hard earthern envelope requires care, and each pod should be carefully uncovered and examined in situ in the soil. Egg-pods with a hard outer cover can be eurropea from the soil and removed to the laboratory for examination. The internal parasites of the post-embryonic stages can be studied by dissection of economiq and rearing from caged hosts.
Dissections are best done on fresh material, but where this is not possible material should be killed in methyl alcohol, or 95 per cent. Dissections are easily accomplished under a low-power binocular microscope, but a careful search between muscles and other organs is necessary to recover the smaller stages and exuviae, which are not necessarily free in the body cavity as eeconomia the later stages.
The best method of caging material for the recovery of emerging parasitic larvae is to use a cage with a false bottom, of some material such as plastic netting or perforated zinc, with the holes slightly larger than those of standard mosquito netting, placed over a vertical-sided tray. This arrangement has the advantage that the hosts need not be disturbed, and larvae cannot be lost in cracks or trodden to death by the host. Experimental infection of hosts with larvae of larviporous species is most success- fully accomplished by teasing out a lightly anaesthetised gravid female in saline and with a h e paint brush placing the larva thus obtained on the stump of a prothoracic leg of the host.
This method allows entry of the parasite larva to be observed but does not affect the host as much as puncturing the body intersegmental membranes, and is more certain than placing the larva on the host and immobilising it until entry has been effected. It is debatable whether any insects are true parasites in the sense used by helmintho- logists. In this work, however, the term parasite has been used to apply to insects feeding internally in one host, and the term predator to those feeding externally and capable of moving from one host to complete feeding on others.
Hence the term egg-predator for the dipterous and coleopterous larvae feeding on egg-pods rather than single eggs. The terms primary and secondary parasite and superparasitisation are used in the sense of Bachmaier The terms used for lx parts of an egg-pod will be found in Waloff and Chapman and Robertson These groups are discussed separately below.
Proctotrupoidea The larvae of all species of this family with known life histories are internal parasites of the eggs of insects of various orders. The genus Scelio and the monotypic genus Lelyidoscelio are conhed to eggs of Acridoidea and are the only genera economja from them.
A REVIEW OF THE INSECT ENEMIES OF ACRIDOIDEA (ORTHOPTERA)
A synopsis of the African species in the form of an extended key, has D. Phoresy of females of Lepidoscelio viatrix by Orthacris spp. Lanham and Evans, ; has been reported.
The females attach themselves h d y to the abdominal intersegmental membranes of the host, not relaxing their hold until jorfan host starts to lay. They are active while the host is ovipositing, running around it and laying as soon as the egg-pod is completed.
Noble found that egg-pods are attractive for 48 hours, but Pemberton and Murai have shown that oviposition can occur at all stages of the development of the jorvan. Before oviposition the female S d i o digs through the froth plug leaving a hole see also Stomorhina lunata or, in the case of egg-pods with a wall, bites a hole through the wall ; the presence of these holes indicates parasitisation.
The eggs are then laid, one in each host egg, by means of an ovipositor which can be extended to a length twice that of the body. The female has a capacity of over one hundred eggs Scelio murai averages Murai, a ; S.
Although superparasitisation is common, only one larva survives in each egg, but the sue of the resulting adult is reduced. Records of sex ratio show pre- dominance of females.
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Pemberton and Murai have shown that un- mated females give rise to male progeny only. The first stage larva fig. The cephalothorax bears a pair of transparent antennae, strong sclerotised curved jaws and, posterior to these, a median sclerotised appendage.
The abdomen bears a pair of tufts of long setae anteriorly, the number of which may prove to be a charac- ter of taxonomic importance, and terminates in a long appendage.
During feeding the abdomen swells in size and considerable movement occurs which macerates the host egg, thus preventing its development. The second instar is fusiform but is not clearly segmented until fully grown, and lacks a respiratory system. The third instar is a typically elongated, segmented hymenopterous larva possessing a tracheal system and spiracles.
The anus is open only just before pupation, which takes place inside the chorion of the host egg. In the absence of diapause, development is rapid, and the egg sometimes hatches within 24 hours and always within two or three days.
Soon after the host eggs would have hatched, the adult parasites emerge by cutting away the end of the host egg. In areas having a cold winter during which there is diapause in the egg of the host, diapause is in the first instar, but it is not obligatory.
Birch found that diapause in S. In warmer areas where there is no diapause there is frequently a delay in the emergence of the adults, which may amount to several months Noble, 1. Accounts from different regions show that the life history is remarkably uniform in the different species, the principal difference being in the stage a t which diapause occm. In all species, only one individual develops fully in each host egg.
Para- sitised eggs are easily recognised, as the chorion becomes more opaque and darker than in healthy eggs. Eggs can be examined for parasitisation by stripping off the chorion after immersion in xylol and observing the contents under a low power binocular microscope. The eggs are minute, spindle-shaped and inconspicuous.
The adults live two or three weeks. Infestations are always characterised by patchiness of distribution, with large variations from sample to sample and locality to locality Richards and Waloff, ; Putnam, ; Zakhvatkin, ; Popov, ; Noble, Host selection appears to depend principally on size Zakhvatkin, ; authors observations rather than on any taxonomic grouping.
Murai found that S. His experi- ments suggest that olfaction is the sense used in h d i n g and identifying the host. It has been noticed that the Desert Locust is rarely parasitised in egg-fields of phase grqark.
This seems to be general with locusts and is borne out by the absence of reports of significant parasitism in gregarious locust populations. It is suggested that this is due to the migratory behaviour of the locusts and that significant parasi- tism only occurs in static populations cf.
This assumes that phoresy is not widespread and does not occur in species associated with locusts. Both are of great interest, as the eggs were on vegetation above ground, instead of being buried. Raoinvestigating Oxya velox in India, found egg-pods laid in folds of leaves and in the bases of plants, so as to be above water level in 0ooded paddy fields. Anastatus coimbatorensis Eupelmidae and Turnidiscupus oophagus Encyrtidae were reared from them, but no biological observations were made.
Liebermann bin Argentina, investigating the oviposition of Swtmsa c l kfound that this species lays on the leaves of Eryngium Umbelliferae ; A w t a – tus bmsanii and Centrodera liebermanmi Aphelinidae were reared from its eggs. These observations indicate that chalcidoid egg-parasites are normally absent from acridoid eggs, which are protected by soil. The authors cited also reared Scelio spp.
Brachycera As far as is known, the larvae of all members of this family are parasitic or pre- daceous.
Those attacking Acridoidea are predators of the eggs. Fourteen genera have been recorded preying on unino, but of these the majority are isolated rearing records, not backed by studies of life history or by data on incidence. Taxonomic works facilitating identification of the adults are available for most areas, but little information, except for isolated descriptions, exists for the larvae.
Greathead attempted to find characters of taxonomic importance for the separation of four species of Systoechus as larvae and pupae but found little in the shape or morphometrics of the third instar larvae ; the pupae are more easily separated, but for reliable identi- fication adults must be reared.
Bombyliid egg predators have been recorded from most areas where Acridoidea are common. Notes on the status of each genus recorded as predatory on eggs are given below. Species of this genus are otherwise widely and exclusively known as predators in the nests of solitary bees, so it seems that this record is an error.
Ancrstoechus Several species of Awtoechus have been recorded as predators, the best known being A. Records of predation cover Africa, the southern Palaearctic region and the American prairies, and destruction of eggs is often heavy. No other indications of the possible hosts of Lomccticr spp.