The influence of two photoperiods (14L:10D and 24L:0D) and four wavelengths of light [white (control), blue (c. 475 ran), yellow (c. 570 nm) and red (c. 650nm)] on development and reproduction of the ladybird, Propylea dissecta (Mulsant), was investigated. The photoperiod of 14L:10D and the white-light wavelength recorded fastest development, maximum survival and reproduction. The developmental and reproductive Performance decreased in the order white > yellow > blue > red. The effect of the wavelength is probably due to the differential predatory response under different coloured arenas.

Poultry have four types of cone in the retina of the eye, and this means that they probably see colour differently from trichromatic humans. Notwith- standing the fact that humans and birds have maximum sensitivity in a similar part of the spectrum (545–575nm), poultry are likely to perceive light from various types of lamp at a different intensity from humans because they are more sensitive to the blue and red parts of the spectrum. Although colour has been confounded with illuminance in many trials, wavelength has an unquestionable effect on poultry production and behaviour. Growth and behaviour responses depend principally on retinal photoreception, whereas photosexual responses are mainly influenced by hypothalamic light reception. In turkeys and chickens growth under red illumination is inferior to that under blue or green light, and this may be a result of birds exposed to red light being more active and showing more aggression than birds exposed to shorter wavelength radiation. In contrast, the easier penetration of longer wavelength radiation to the hypothalamus makes red light more sexually stimulatory than blue or green, although the hypothalamic photo- receptors are more sensitive to blue/green light when illuminated directly. Egg production traits, however, appear to be minimally affected by wavelength.

An efficient algorithm to compute upper and lower bounds for the first-passage time in the presence of a second absorbing barrier by means of a continuously differentiable decomposable process, e.g. a smooth function of a continuously differentiable Gaussian vector field, is given. The method is used to obtain accurate approximations for the joint density of the zero-crossing wavelength and amplitude and the distribution of the rainflow cycle amplitude. Numerical examples illustrating the results are also given.

Cassava leaves damaged by green spider mite, Mononychellus tanajoa (Bondar) and undamaged leaves were analysed in the laboratory for chlorophyll content by spectrophotometry. Proximate analysis was also carried out on the leaves in the laboratory using the Association of Official Analytical Chemists methods.

More light was absorbed by the chlorophyll extract from the undamaged leaves than in the mite-damaged leaves. More light was also absorbed at the wavelength of 663 nm than at 645 nm. The concentrations of chlorophyll a and b were higher in the undamaged leaves than in the mite-damaged leaves. The concentration of chlorophyll a was higher than that of chlorophyll b both in the undamaged and mite-damaged leaves.

Mite-damaged leaves weighed less than the undamaged leaves, both when fresh and when dried. The proximate products values were less in the mite-damaged leaves than in the undamaged leaves.

As has been shown by de Maré, in a stationary Gaussian process the length of the successive zero-crossing intervals cannot be independent, except for the degenerate case of a pure cosine process. However, no closed-form expression of the distribution of these quantities is known at present. In this paper we present an accurate explicit approximative formula, derived by replacing the Slepian model process by its regression curve.