Feeding behaviour of adults of Pieris brassicae (L.) in a laboratory culture

Abstract

SummaryOnly a few individuals in the first generation of adults of Pieris brassicae (L.) reared in captivity will feed on artificially prepared flowers. By breeding from the eggs laid by these individuals and from a few others which have been helped to feed it is possible to maintain the stock. In each successive generation a few more individuals feed, and after about four generations most of the insects feed voluntarily. Finally, after many generations, all the insects use the flowers, and the experiments described are concerned with this adapted stock.Many factors influence the attraction of the insects to the artificial flowers and the volume of food taken. Colour, blue or yellow, is responsible for attracting the adults to the flowers, and it is only when they are very close to the flowers and under the stimulus of colour that they show any detectable reaction to the odour of the honey solution in the flowers. Larger blue flowers are more attractive than smaller blue flowers.The insects find the artificial flowers more easily, at first, if they are high in the cage. More honey solution is taken at 30 than at 20°C. and more in a large cage than in a small cage. When given a choice, the insects take more 10 per cent, (v/v) than 1 per cent, (v/v) honey solution and more 20 per cent, (v/v) solution than 10 per cent, (v/v) solution. When offered two of these solutions in separate cages the insects at first take less of the 1 per cent, solution than of the 10 per cent, solution. Later, presumably in an effort to obtain sufficient nutriment, they take more of the weaker solution than of the stronger solution. The insects live for a much shorter time on the 1 per cent, solution than on the 10 per cent, solution. Fresh honey solution is preferred to a solution 4–5 days old, and older honey solution is quite unsuitable as food. When the survival of adults fed on honey and sucrose solution is compared it is found that females, especially, survive longer when feeding on honey.About 50 per cent, of the adults fed on 10 per cent, honey solution in the normal stock cage under glasshouse conditions live for 18 days. Very few survive for longer than 36 days. Starved insects all die by the llth day under similar conditions. When starved at 12·5°C. and 60 per cent, relative humidity, about half the males live for 17 to 19 days, but all are dead by about the 23rd day, whereas half the females live for about 29 days and some survive up to 40 days.