The embryonic apolyses of Schistocerca gregaria (Orthoptera)

The origin and differentiation of the ecdysial glands and the appearance of the cuticles were studied in embryos of Schistocerca gregaria at corresponding stages. The development of the cuticle was also studied in headless embryos explanted in vitro.     

The germ-free culture of desert locusts, Schistocerca gregaria

A technique is described for rearing germ-free desert locusts. Axenic insects appeared to develop and reproduce normally, therefore it is concluded that the gut bacterial flora does not contribute significantly to locust nutrition. However, it is suggested that the gut flora may benefit its host by contributing to the locust's defences against attack by pathogenic microorganisms. The results of morphometric measurements are discussed in terms of the bacterial origin of the so called phase pheromone, locustol. No evidence was found to support the hypothesis that microbial activity restricts gut carbohydrase.     

Allatectomy and sexual receptivity in females of Schistocerca gregaria

The removal of the corpora allata from immature females of Schistocerca gregaria causes the insects to enter a phase of permanent defence towards courting males. Operated control females copulate often, although they do not appear to show an active form of sexual display or attraction. Implanted corpora allata fail to restore sexual receptivity or normal ovarial development in the allatectomized females due to the inactivity of the denervated glands. The observations are discussed in relation to findings in other locusts, grasshoppers, and crickets.     

An ultrastructural study and stereological analysis of the colon wall in the cockroach Periplaneta americana

The colonic epithelium has been examined for ultrastructural evidence of physiological activity. The cells show extensive folding of the apical plasma membrane, associated with mitochondria and an internal coating of particles about 120 Å diameter. Anteriorly many apical infoldings are dilated at the tip to form substantial extracellular spaces up to 0.8 μm wide. Narrow intercellular channels are present, opening to the haemolymph side of the epithelium. Pinocytosis is seen frequently at the basal surface. The surface densities of apical plasma membranes were not significantly different in the posterior mid-gut and colon. Similarly the volume densities of mitochondria were equal in the colonic epithelium and rectal pads, but the surface density of outer mitochondrial membranes was greater in the colon. It is suggested that the colon may absorb organic solutes from the gut lumen.     

The Comstock-Kellogg glands in female Schistocerca gregaria: Their eversion and haemocoelic pressure

The glandular pouches of Comstock and Kellogg on the genital chamber of females of Schistocerca gregaria can be everted and displayed by exerting firm pressure on the tip of the abdomen. The glands evert when the ovipositor values are extended and the gland apertures pass the posterior border of the sub-genital plate. This process has not been observed to occur spontaneously in females in this colony. Increasing the pressure in the haemocoel by means of a saline reservoir is effective in causing gland eversion only when pressures in excess of 75 mm mercury are used: these pressures cause abnormal distortion in the insect. Haemolymph pressure monitored in digging and egg-laying females varies only slightly from atmospheric pressure and never approaches the pressures required to enforce gland eversion. Gland eversion is not observed in digging females, but is difficult to observe in females in the act of laying, due to the presence of egg-pod secretion.These observations are discussed in relation to the structure of the pouches and other information concerning their possible functions in the female desert locust.     

Control of melanization in first instar larvae of Schistocerca gregaria

Melanization in first-instar larvae of Schistocerca is controlled by a hormone released from neurosecretory axon terminals of the fine nerves posterior to the metathoracic ganglion. The hormone is not detectable in the haemolymph before the embryonic ecdysis but is present within seconds after the ecdysis has started. It is suggested that horizontal displacement of the embryonic cuticle is the trigger for the release of the hormone and that the prothoracic ganglion forms part of the neural pathway between the sensory input caused by ecdysis and the release of the hormone.     

Comparison between the sclerotization of adult and larval cuticle in Schistocerca gregaria

Femur cuticle from fifth instar larvae of the desert locust, Schistocerca gregaria, has been characterized with respect to composition, rate of deposition, and rate of sclerotization. The results are compared with those from adult cuticle of the same species. The protein compositions of the two types of cuticle are very similar, but the rates of deposition of both protein and chitin are different. The main difference is, however, that sclerotization is restricted to the first day after ecdysis in larval cuticle, whereas in adult cuticle sclerotization continues for at least a couple of weeks. The result is that the endocuticle remains untanned in the larvae, whereas in the adults the whole cuticle becomes tanned.     

Mechanisms of pheromone inactivation in the gut of Periplaneta americana

The sex attractant of the cockroach, Periplaneta americana, has been shown in earlier work to be largely inactivated by dissected midgut from males and from mated females. It is only slightly inactivated by the midgut from virgin females. In this paper, the sex pheromone inactivating system is further studied and shown to be active in late instar larvae of both sexes. In the male this pheromone inactivation is inhibited by piperonyl butoxide, a microsomal oxidase inhibitor. This compound appears to act on the midgut tissue directly. In the mated female, piperonyl butoxide has little effect. When the pheromone inactivating capacity is partitioned into soluble and tissue components, it appears that the soluble component is most active in the male, whereas the tissue component is most active in the female. Evidence from heat inactivation, trichloracetic acid precipitation, and the use of soy bean trypsin inhibitor, as well as the time course of the reaction, suggest that the factor or factors inactivating pheromone are proteins, probably enzymes. Evidence that at least part of the pheromone inactivating capacity is due to microsomal oxidases is considered. It is also observed that both pheromone and piperonyl butoxide absorb to membranes.     

Behavioural responses to female sex pheromone components in Periplaneta americana

Female American cockroaches, Periplaneta americana, release two sex pheromones, periplanone-A and periplanone-B, each of which is perceived by a specialized receptor type on the male antennae. This study investigates whether male behavioural responses to both components may differ qualitatively or quantitatively. Running, upwind orientation and wing-raising were evoked by stimulation with either component. The intensity of running increased with stimulus concentration in much the same way for both substances. However, the relative effectiveness of periplanone-A was 30 times lower in behavioural assays than in the electroantennogram. Behavioural responses to periplanone-B declined faster and were more easily adapted by repeated stimulation than those to periplanone-A. It is hypothesized that periplanone-B is responsible for long distance attraction while periplanone-A influences male behaviour near the female.     

The need for high levels of phenylalanine in the diet of Schistocerca gregaria nymphs

It has been demonstrated that an apparently good, nutrient-rich plant can be relatively short of phenylalanine for fifth-instar nymphs of Schistocerca gregaria. Supplementary phenylalanine invariably increased the efficiency of conversion of ingested food to body substance, showing that this was the limiting nutrient. Relatively large quantities of phenylalanine are required for cuticle protein over a few days in the first half of the instar, which is when this amino acid is at a premium.     

The pattern of ecdysone levels during development in the desert locust, Schistocerca gregaria

A simple chemical assay, sensitive to picogram amounts (10^?12 g) of ecdysones in crude biological materials is described. By a simple, rapid purification procedure followed by conversion to their trimethylsilyl ethers, ecdysones are determined quantitatively by gas chromatography with an electron capture detector. The method has been applied to the determination of ecdysones in the fourth and fifth instars of the desert locust. 20-Hydroxyecdysone is always present in higher concentration than ecdysone and the former rises to a sharp maximum 1 to 2 days before ecdysis.     

Haemolymph lipase activity in the American cockroach, Periplaneta americana

The haemolymph of the cockroach, Periplaneta americana, has been shown to possess pronounced lipolytic activity. The enzyme may be considered a ‘true’ lipase because of its ability to hydrolyse long chain fatty acid glycerides. The enzyme exhibits dual optima at pH 4·9 and 7·0 and is inhibited by fluoride ion. Lipase activity in the intact cockroach is unaffected by the corpus cardiacum hypolipemic factor; however, prolonged periods of starvation result in a significant decline in enzyme activity.     

One trial learning in the American cockroach, Periplaneta americana

A new and simple method of training intact cockroaches was designed. (1) Cockroaches were maintained before and during the experiment with a high motivation to look for sugar. They were kept in a chamber with water and yeast extract ad libitum but without any sugar. (2) Cockroaches were individually trained to associate two artificial scent signals, i.e. menthol and vanilla, with sugar and salt solutions. Discriminatory learning performance was measured by testing the scent preference before and after training. Care was taken to exclude other than olfactory cues in the discriminatory paradigm. (3) Cockroaches exhibited a spontaneous initial preference for vanilla over menthol. This preference could be modified by training. The insect showed fast learning and long retention. One training trial was enough to reverse the initial preference with a significant retention after 7 days. Reversal of trained preference was accomplished by retraining. (4) The method provides an opportunity to study sensory performance and memory consolidation in cockroaches.     

Circadian rhythmicity in the nervous system of the cockroach, Periplaneta americana

Diurnal rhythmicity of nervous activity in Periplaneta americana was investigated, using acetylcholine (ACh) content, acetylcholinesterase (AChE) and spontaneous electrical activities as indices. AChE and electrical activities were maximum at 0 hr and minimum at 12 hr, while ACh showed an opposite rhythm. Central nervous system extract from cockroaches at 12 hr elevated the electrical activity while 0 hr-extract exerted inhibition. Lower concentrations of ACh had an elevatory influence while higher concentrations inhibited the electrical activity. A hypothesis is proposed, suggesting synthetic and releasing phases of ACh in a regular diurnal cycle, to explain the results obtained.     

Ecdysteroids in the developing eggs of the desert locust, Schistocerca gregaria

Ecdysteroid levels in the developing eggs of Schistocerca gregaria were determined, at daily intervals, using gas chromatography and electron capture detection of ecdysteroid derivatives. Ecdysone and 20-hydroxyecdysone were present both as the free ecdysteroid and as polar conjugates. Total ecdysteroids reached a maximum of 40 ng/egg with ecdysone contributing the greater part.     

Bursicon-mediated control of tanning in melanizing and non-melanizing first instar larvae of Schistocerca gregaria

Both melanization and sclerotization in first instar Schistocerca larvae are shown to have a common hormonal control mechanism. This hormone is shown to be analogous to bursicon, the tanning hormone of other insects, by the standard blowfly bioassay. The hormone is identical in both melanizing and non-melanizing first instar larvae of Schistocerca.     

Componental analysis of the ocellar electroretinogram of the locust, Schistocerca gregaria

Ruck's componental analysis of the ocellar electroretinogram (ERG) has been reappraised using techniques of signal averaging and waveform subtraction. Components (1), (3), and (4) can readily be isolated in the locust ocellus but component (2) as recorded in the locust ocellus is probably an artefact. Component (1), produced by the receptor cells, only contributes significantly to the total ERG at higher light intensities and it is this contribution which changes most with the degree of light and dark adaptation employed in these experiments. Component (3), the response of the second-order neurones, indicates that the majority of second-order neurones hyperpolarize on illumination of the ocellus. Component (4), the afferent activity of the second-order cells, indicates that more than one afferent axon is involved in the production of off spikes in the locust ocellus.     

Fine structure of the first optic ganglion (lamina) of the cockroach, Periplaneta americana

The structural organization of the first optic ganglion (lamina) of the cockroach (Periplaneta americana) was investigated by the use of light and electron microscopy. Each compound eye of the cockroach is composed of up to 2000 visual units (ommatidia) of the fused rhabdom type. The ommatidia themselves consist of eight receptor cells which terminate as axons in either the first or second optic ganglion. Three different short visual fibre types end in two separate strata in the lamina, and one long fibre type ends in the second optic ganglion. Monopolar second-order neurons with wide field branching patterns in the middle stratum of the first synaptic region have postsynaptic contacts with short visual fibres. Horizontal fibre elements with branching patterns at different levels of the lamina apparently form three horizontal plexuses with presynaptic and/or postsynaptic connections to first- and secondorder neurons. The lack of well-organized fibre cartridges containing a constant number of first and second order neurons in each fascicle and the presence of only unistratified wide field monopolar cells could represent, as compared to other insect orders, a primitive stage in the development of the first optic ganglion.     

Histopathology of secondary infections of Malpighamoeba locustae (Protozoa,Amoebidae) in the desert locust, Schistocerca gregaria (Orthoptera,Acrididae)

Schistocerca gregaria, the desert locust, harbors the protozoan parasite Malpighamoeba locustae. Twelve to 16 days after infection, trophozoites begin to multiply rapidly inside the Malpighian tubules of the gut. Swelling and rupture of the Malpighian tubules leads to the release of large numbers of cysts and trophozoites into the hemocoel. The classic insect defense response results in these cysts and trophozoites becoming encapsulated by the hemocytes of the host. Hemocytes of the phagocytic type become attached to, and lodged between, a variety of tissues and organs of the locust and black hemocytic capsules are produced. The extent to which the different tissues are involved is graded. Some tissues are completely blackened and encapsulated by masses of hemocytes but others are so lightly affected that the small specks of blackened pigment they lay down are discernible only on close examination. The trophozoites themselves do not divide outside the Malpighian tubules. The graded response in the host tissues is related to (1) the presence of sheets and lobes of fat body and (2) the presence of phagocytic hemocytes.