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.

The major components of the tracheal system of insects are an extension of the exoskeleton, and the size of the exoskeleton is fixed in the adult stage, so any increase in metabolic demand that may accompany reproduction must be met by a relatively unaltered tracheal system that the female set in place at ecdysis, when entering adulthood. Acute hypoxia tends to elicit an increase in ventilation in insects, and here, I observe increased interburst VCO2 release, and a tendency towards a more continuous gas exchange pattern being preferred over discontinuous gas exchange when Blaptica dubia and Eublaberus posticus are exposed to a descending regime of hypoxia. Additionally, higher temperatures appear to increase sensitivity to hypoxia in these species, an expected result because both species, like most ectothermic animals, display a Q10 effect, increasing metabolic rates as temperature increases. The reproductive mode of B. dubia is considered to be lecithotrophic pseudoviviparity (or type A ovoviviparity), and by the time the embryos are born, they have more than doubles in volume from the time of oviposition. This gain is apparent in the wet mass of the embryo, with no change occurring in dry mass. The egg mass that can be attributed to water begins at 39% at oviposition and increased to nearly 82% at hatching. The metabolic rates of females and embryos increase as embryonic development progresses, but bomb calorimetry reveals that energy content of the embryos does not change. It is possible that these embryos gain some nutrition from the mother during embryonic development, but direct evidence remains to be demonstrated. Blaptica dubia and Eublaberus posticusare both blaberid species that display the same reproductive mode, pseudoviviparity, with incubation occurring in a brood sac. Comparisons between the reproductive traits of B. dubia and E. posticus reveal that the two species have similar reproductive periods, interbirth periods, and clutch sizes to one another, and that both have reproductive cycles and incubation times intermediate to oviparous species and the one species of cockroach that some consider to be truly viviparous (Diploptera punctata). However, whereas adult female E. posticus are larger than female B. dubia (E. posticus non-gravid female mass: 2.91 +/- 0.42 g, 20; B. dubia non-gravid female mass: 2.60 +/- 0.40 g, 20), the offspring of B. dubia are larger than those of E. posticus at the time of birth (B. dubia neonate mass: 24.70 +/- 4.01 mg, 19; E. posticus neonate mass: 22.40 +/- 1.36 mg, 19). Both gravid and non-gravid female B. dubia respond similarly to acute hypoxia exposure, increasing mean total VCO2. However, the reproductive state does not appear to exacerbate, nor dull, the acute response to hypoxia. Gravid and non-gravid female B. dubia were exposed to chronic hypoxia for 30 days and 45 days. Relatively high mortality was observed in nearly all chronic hypoxic treatment groups as compared to controls at 21 kPa O2. Comparing treatment groups to controls maintained at 21 kPa O2, embryo mass was not decreased, nor was embryo VCO2 at day 30. Adult female B. dubia metabolic rates did not show a consistent change in response to chronic hypoxia, but decreased metabolic rate was observed in the non-gravid B. dubia exposed to chronic 4 kPa O2, an observation that is consistent with past studies in insects. Survival rates were lower for both gravid and non-gravid females in 4, 8, and 12 kPa O2, as well as in 15 kPa O2 in gravid females, as compared to 21 kPa O2. Gravid females experiences a decreased survival rate compared with non-gravid females at 12 and 15 kPa O2, but gravid and non-gravid females had similarly low survival rates at 4 and 8 kPa O2. This difference in survival rates suggests there is a cost associated with carrying an ootheca in a brood sac, resulting in an increased sensitivity to hypoxia, at least over a long period of time.