Organic agriculture can and should play an important role in solving future challenges in producing food. The low level of external inputs combined with knowledge on sustainablity minimizes environmental contamination and can help to produce more food for more people without negatively impacting our

Nine glucosides tested as feeding stimulants for Pieris brassicae larvae were effective. The tetraacetates of three of them were not. Two of the glucosides (glucocapparin and glucoiberin) were active at 0.333 × 10−6 molar in the diet and at 0.333 × 10−4 molar all were effective. Usually all the larvae in a test do not feed and the increase in effectiveness with concentration, which is observed in groups, is largely brought about by a progressive increase in the number of larvae which actually feed, though with some glucosides an increase in the average frass production of the feeding larvae was found. The relative effectiveness of the glucosides as feeding stimulants changes with concentration. At a concentration of 0.333 × 10−5 molar, glucocapparin gave the best result while at 0.333 × 10−3 molar concentrations glucotropaeolin was most effective. Neither of these glucosides has been reported to occur in cabbage leaves. ZUSAMMENFASSUNG SENFÖLGLUKOSIDE ALS FRASSTIMULANTIEN FÜR PIERIS BRASSICAE‐RAUPEN BEI EINER HALBSYNTHETISCHEN DIÄT Neun als Fraßstimulatoren für Kohlweißlingsraupen geprüfte Glukoside erwiesen sich als wirksam. Die Tetraacetate von drei von ihnen waren es nicht. Zwei der Glukoside (Glukokapparin und Glukoiberin) waren 0,333 × 10−6 und 0,333 × 10−4 molar in der Diät wirksam. Gewöhnlich fressen in einem Versuch nicht alle Raupen und der Anstieg der Wirksamkeit mit der Konzentration, die gruppenweise beobachtet wird, läßt sich hauptsächlich durch ein zunehmendes Anwachsen der Anzahl von Larven feststellen, die wirklich fressen, obwohl bei einigen Glukosiden ein Anwachsen der Kotproduktion der fressenden Larven gefunden wurde. Die relative Wirksamkeit der Glukoside als Fraßanregungsmittel ändert sich mit der Konzentration. Bei einer molaren Konzentration von 0,333 × 10−5 ergab Glukokapparin den besten Erfolg, während Glukotropaeolin bei 0,333 × 10−3 molarer Konzentration am wirksamsten war. Keines dieser Glukoside ist bisher in Kohlblättern nachgewiesen.

No abstract

The general insecticidal properties of bis (his-dimethylamino phosphonous) anhydride (anhydride), bis (dimethylamino) fluorophosphine oxide (oxide), diethyl paranitro-phenyl phosphate (E ~o o ) , and sodium fluoroacetate (acetate) are described. All are toxic to aphids when infested plants are dipped in solutions. Although this is thought to be a contact action the possibility that the materials are first absorbed by the leaves and that the aphids are killed by imbibing toxic sap is not excluded. The order of decreasing toxicity by dipping is E6oo>acetate> anhydride =oxide. At the lowest concentration giving a complete kill of aphids, the anhydride is the most persistently effective of the four compounds. E6oo is the most phytotoxic compound.When applied to the roots the order of decreasing toxicity is acetate>oxide > anhydride > E 600 in sand and soil, and acetate > oxide > anhydride = E 600 in culture solution. The anhydride and acetate are more persistent in the plants than the oxide and E600. The margin of safety between insecticidal dosage and phytocidal dosage is appreciably larger with the acetate than with the other three compounds. When equal dosages are administered to plants by the cut tap root technique the order of decreasing toxicity to aphids is seen to be acetate > oxide > E6oo > anhydride. All compounds, except possibly E600, appear to be absorbed by the intact roots of the plants. Systemic insecticidal action following application made to the leaves of the broad bean is easy to demonstrate with the acetate, demonstrable with difficulty with the anhydride and not at all with E6oo and the oxide.Only the oxide is sufficiently volatile to kill insects by a fumigant effect either as the pure substance or after absorption into the plant. Plants treated with it give off a toxic vapour which may be collected by condensation and shown to be systemically active. The material concerned is presumed to be the unchanged oxide.Sodium fluoroacetate is an extremely effective systemic insecticide whether applied to the leaves or the roots of the broad bean. It is apparently not phytotoxic at several times the concentration necessary for insecticidal action but may prove to be too generally toxic or persistent for practical use.

The work described in this paper forms part of an investigation into the conditions which influence the breeding of Pieris brassicae (L.) in captivity. Observations have been made on the behaviour of the females at the time of oviposition, on factors which influence oviposition, on the appearance and weight of the eggs and on their fertility and hatching.Females which are ready to lay seek out green surfaces and, as they respond eagerly to plants from which they are separated by glass, it seems that plant odour plays little part in the attraction. Once they have alighted, however, the insects drum on the surface with their fore legs to test its suitability. Normally they lay only on plants which contain the mustard-oil glucosides, but they have been observed to oviposit on broad bean (Vicia faba), on which the larvae do not survive. Sinegrin applied to green paper stimulates the female to lay. Provided she is standing on an acceptable surface she will oviposit on any other surface, for example, filter paper or glass. The eggs are normally deposited on the under surface of the leaves. This is largely due to a preference for the physical underside but the insects also seem to prefer the morphological under surface of the leaf to the upper surface. When laying an egg, the female locates one previously laid with the tip of her abdomen and so builds up the regularly arranged batches.The females lived and oviposited as well in small cages as in large cages. They laid more eggs per day, and more eggs in a batch, at 30°C. than at 20°C. Both numbers increased until the female was about six to seven days old and then declined. Oviposition occurs at low light intensities. Fertilised females laid very many more eggs than virgin females. Oviposition occurred two to three days after copulation, and most females oviposited six or seven times in eight days. The number of eggs laid by starving insects is low: it is higher for insects given water or one per cent, honey solution and very much higher for insects given ten per cent, honey solution. Sucrose solutions are as satisfactory as honey solution.When first laid, the eggs of P. brassicae are yellow in colour and become more orange as they develop. Some batches of newly laid eggs are of a distinctly darker yellow than others but, as it is believed that the eggs are fertilised only just before oviposition, it seems that this colour difference cannot be due to the eggs being in somewhat different stages of development. The number of ribs on the shells seems to vary in different cultures.Batches of eggs which are laid within an hour of each other may begin to hatch several hours apart, and the time taken for all the eggs in one batch to hatch was found to range from two hours to about seven. A fertilised female lays scarcely any infertile eggs. The fertility after one mating falls below 100 per cent, after about 14 days, but normally the female mates again before this time. Temperature naturally affects the time taken by the eggs to hatch. The shortest time was about 3¾ days at 28°C.; the longest observed was 17 days at 12·5°C.The eggs cannot be stored for more than ten days at 3·5°C. and 50 per cent, relative humidity. Eggs will develop and hatch at very low humidities. If the eggs are detached from the surface on which they are laid by the use of acetone their capacity to develop and hatch in air dried over phosphorus pentoxide is substantially reduced.