This study Is an investigation into the behaviour of male bushcrickets of the genus Metrioptera. The situation investigated was that arising when the males of different species are placed in the same enclosure. A large number of such experiments was made and in each case observations were made on the movements of the insects, particularly with respect to one another. Their stridulations were recorded and subsequently analyzed with a view to detecting influences by the song of one insect upon song production by the other. Attempts were made to relate the behaviour to that observed in similar circumstances when the two males belonged to the same species. In the latter cases, clearly recognisable aggression and homosexual courtship were much commoner, and there was a much stronger tendency for the defeated insect to return to the victor in one species, influence of pre-conflict caging conditions was studied. Four species of Metrioptera were utilised: M. roeselii (HAGENBACH), M. brachyptera (L.), M. bicolor (PHILIPPI), and M. sepium (YERSIN). Nearly all of the experiments were confined to the first three species. It was found that the stridulations of roeselii and bicolor tended to inhibit song output in brachyptera. In interactions between roeselii and bicolor, either insect could be inhibited, but it was more often bicolor. A visit was made to a German locality where roeselii and bicolor occurred naturally in the same place, and inhibition effects were observed to take place between them in the field. One brachyptera out of thirteen tested produced chirps with more syllables than usual, when exposed to roeselii song. It did not modify its chirps in response to bicolor song, perhaps because of the more discrete nature of the latter. The phenomenon is discussed in relation to Broughton'S (I965) discovery of song modification in Platycleis denticulata (PANZER).

Reproductive interference occurs when individuals direct sexual behaviours towards other species and this causes a reduction in the fitness of one or both of the participants. While initially considered to be little more than an aberration, reproductive interference is increasingly recognised, not just as a factor in determining species co-existence and community dynamics, but also as an opportunity to further our understanding of sexual selection. In this thesis I investigate the causes and consequences of reproductive interference between several species of true bugs (Order: Hemiptera) in the family Lygaeidae. These species have a polgynandrous mating system, in which both males and females mate multiple times. I found that the interspecific mating attempts often witnessed in these bugs is likely a consequence of this mating system, as potential cues for species discrimination, in the form of cuticular hydrocarbons, are available and can be utilised by the bugs in some contexts. This is further supported by the finding that pre-copulatory selection on factors such as diet and chemical protection are weak in these insects. Furthermore, my work highlights the context-dependant nature of both the fitness costs associated with reproductive interference, and also of the bugs' intra-specific behaviour. When housed in groups, female Lygaeus equestris did not show consistent fitness losses in response to harassment by either conspecific or heterospecific males, despite previous evidence showing that such males inflict costs on both egg production and longevity when interacting one-to-one. This, combined with the finding that male L. equestris alter their mate-guarding behaviour in the presence of other males, highlights the potential of behavioural flexibility to influence the outcome of inter-species interactions, and the importance of context when attempting to measure phenomena such as reproductive interference.

The structure of insect cuticle has been reviewed briefly and an account given of the processes by which hardening (tanning) occurs after the moult. The sclerotin wall of the cockroach ootheca is formed by the intermingling of the accretions of the left and right colleterial glands. This system, because of its comparative convenience, is studied with a view to shedding light on the sclerotin formation in the cuticle. With reference to their role in sclerotization, the properties of insect blood and cuticle oxidases are reviewed and comparisons made with the animal and plant enzyme grouse they most resemble - tyrosinases and laccases. The function of copper in these oxidases is discussed. A method was developed for determining the protein concentrations, in the presence of phenolic compounds, of the diluted secretion from the left colleterial glands of Periplaneta. This involved digestion (6N-HCl, 6 hours) of the protein followed by estimation with ninhydrin of the total amino acids in the hydrolysate. Investigation of the properties of the copper-containing (0.1-0.2%) phenoloxidase of the left colleterial gland showed that the enzyme is specific towards diphenols (especially ortho-) and is therefore not a tyrosinase. In the majority of its properties the oxidase resembles a laccase, although it is more specific than the plant enzymes. Phenolic substrates bearing an amino group in the side chain are not active - a property which clearly distinguishes the cockroach phenoloxidase from the blood tyrosinase of insects. Towards certain substrates (catechol, hydroquinone, homoprotocatechuic acid) activity is unexpectedly stable to boiling while towards others (protocatechuic acid and its aldehyde) it is destroyed. Possibly non-enzymic, as well as enzymic, activity exists. The effect of some substances (detergents, dopa, catechol, tyrosine, ascorbic acid) on the activity of the phenoloxidase towards protocatechuic acid (3 μmoles) is measured. The stimulation caused by ascorbic acid (0.15 andmu;moles) is related to the possible requirement of cuprous ions for enzyme activity. The phenoloxidase activity which resides in a articulate fraction of the gland secretion, is (unlike other copper oxidases) not inhibited by metal chelating agents, such as phenylthiourea, diethyldithiocarbamate, ethylenediaminetetracetic acid and 4-chlororesorcinol, in the presence of sodium phosphate buffer (0.1M -, pH 6.8). Cyanide and borate are effective inhibitors, however. Varied attempts to purify the participate enzyme and thus to fractionate it from the prosclerotin or structural protein met with little success. The specific activities (Q_O₂'s) of the supernatants obtained after high speed centrifugation (100,000-182,000 andtimes; g) are approximately five to ten times higher than those (3.93±1.15(10)) of untreated enzyme preparations. An examination of this "purification" led to the conclusion that the enzyme activity appeared to be rather dependent on the state of aggregation of the protein particles. Further evidence of this effect was inferred from the stimulating action of anionic (deoxycholate) and neutral ("Tween") detergents (added prior to buffering) upon phenoloxidase activity. Prior to the institution, as a regular procedure, of dialysis (0.01M-NaCl) of the colleterial gland secretion (to remove endogenous phenolic compounds), a long induction period (ca. 20-60 mins.) before commencement of oxygen uptake by enzyme and substrate was frequently observed. This long period was minimized by the addition of right gland homogenate or ascorbic acid. In section II, the phenolic compounds found in insect cuticle and in cockroach colleterial glands were examined with reference to their biosynthesis and to their role in sclerotization. Protocatechuic acid, its 4-o-β-D-glucoside and p-tyrosine were identified (chromatographically and spectrophotometrically) in homogenates of left colleterial gland. After aerobic incubation (37°C) of these homogenates substances strongly resembling catechol and tyramine were separated by paper chromatography and identified by their u.v. spectral properties after elution. Protocatechuic acid and p-tyrosine, when added (with and without right gland preparation) to homogenates of left glands, increased the production of catechol and tyramine respectively. From densitometric measurements of ferric chloride/ferricyanide sprayed paper chromatograms the aerobic conversion by left gland homogenate of p-tyrosine (1 andmu;mole added) into tyramine (0.62 andmu;moles) was demonstrated, The amine was also separated by absorption on Amberlite-IRC (H⁺). The decarboxylase systems responsible for catechol and tyramine production, whether induced or not, were heat labile. There is some manometric evidence that the former enzyme is located in right gland cells while the latter is present in the larger gland tissue. These findings are made uncertain by the retardation of the reactions in presence of inorganic buffers (and an anaerobic atmosphere) and by extraneous gas evolution particularly during incubation of mixed homogenates of both glands. In the light of some evidence, the possibility that tyramine might be enzymically oxidized by homogenates of left gland is weighed. The significance of such a reaction, together with the decarboxylation of p-tyrosine and protocatechuic acid, is discussed with regard to the biosynthesis of tanning quinones from the p-tyrosine of the insect blood.

Endosymbiosis has been a major driver of evolutionary diversification of eukaryotes. However, symbiosis can create conflict between partners and symbiont density is often tightly regulated within hosts to ensure optimal functioning of the holobiont. The horticultural pest insects, citrus mealybugs, make an intriguing and potentially-powerful case study for endosymbiosis, harbouring two obligate, nutritional, vertically transmitted bacteria: Tremblaya princeps and Moranella endobia, in a nested mutualism. In this thesis, I examine the variation in the density of each of these obligate symbionts in citrus mealybugs under controlled environmental conditions, using qPCR, as well as the diversity of facultative symbionts that infect the mealybugs using next-generation sequencing and conventional targeted PCR. Citrus mealybugs were found to harbour Wolbachia, Spiroplasma, Cardinium and Rickettsia, which have been found to impact the fitness of their hosts in other insect species, whereas long-tailed mealybugs were not found to harbour any of these bacteria, but the symbiont communities in both species were found to be dominated by their obligate symbionts. The density of the two obligate symbionts varied by up to six-fold between different populations kept under identical environmental conditions and a hybridisation experiment indicated that M. endobia and T. princeps density may be controlled by symbiont and host genotype respectively. However, symbiont density was not found to correlate with life-history traits in the laboratory, the ability of mealybugs to exploit different plant species, or the susceptibility of the mealybugs to insecticide and artificial reduction of symbiont density by heat-stress also had no effect on host fitness. Citrus mealybugs harbour seemingly superfluous symbionts with no clear fitness costs or benefits.

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No description available.

No description available.

The individual and combined effects of the endogeic and epigeic groups of earthworms on the growth of Chinese cabbage (Brassica rapa), and on the subsequent growth and development of the generalist sap-sucking herbivore Myzus persicae were determined in separate pot experiments. Many previous studies have investigated the relationship between soil biodiversity and aboveground plants, but few researches have considered the indirect interaction between soil biota and above-ground aphids. In this study the individual effects of Aporrectodea rosea and Allolobophora chlorotica and the combined effects of A. rosea and A. chlorotica, Aporrectodea caliginosa and Satchellius mammalis, A. chlorotica and S. mammalis, and A. rosea, A. caliginosa, Lumbricus rubellus and S. mammalis on plant morphology and physiology and aphid development (nymphs day-1, fecundity and number of adults) were investigated. Plant growth was affected by the presence of A. rosea which caused increases in plant biomass, height of plant, leaf surface area and specific leaf area (SLA). Mean number of leaves per plant was unaffected by worm density. In contrast, increasing density of A. chlorotica had no effect on any aspect of plant performance. The combined effect of A. rosea and A. chlorotica resulted in a similar increase in plant biomass to A. rosea alone. While the combined effects of A. caliginosa and Satchellius mammalis, A. chlorotica and S. mammalis and A. rosea, A. caliginosa, L. rubellus and S. mammalis caused increases in all plant parameters except leaf number. Additionally, the individual effect of A. rosea and the combined effects of A. caliginosa and S. mammalis, A. chlorotica & S. mammalis and A. rosea and A. caliginosa, L. rubellus and S. mammalis resulted in increased in leaf nitrogen concentration. Aphid development was also affected by the presence of earthworms. The nymphs day-1, fecundity and numbers of adults were significantly increased with increases in earthworm densities. The interaction between all groups of earthworms and their influence on aphid growth showed that the combined effect of two different groups was greater than the individual groups. Proteomic techniques were used to compare protein patterns in the plants. The combined effects of A. caliginosa and S. mammalis, A. chlorotica and S. mammalis, A. rosea, A. caliginosa, L. rubellus and S. mammalis earthworms on plant resulted in differences in number and kind of protein between plant treated with earthworms and the control, but no significant difference in proteins volume. Effects of earthworms on plant growth and aphid development are shown to be modified by increasing density and interactions between different species and functional groups of earthworms.

No description available.

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