During the last year, while I was engaged in work on stored product pests for the Infestation Branch of the Ministry of Food, the necessity arose for identifying Lepidopterous larvae damaging stored food. It was soon found that with few exceptions the available descriptions of these larvae are quite inadequate, as they are usually based entirely on colour, and it became necessary to employ more precise methods. The arrangement of the setae (chaetotaxy) together with other structural characters proved to be reliable for distinguishing the species. By these means those concerned should be able to identify without undue difficulty most of the moth larvae they are likely to encounter. Altogether 35 out of some 70 species which have been found associated with stored products in all parts of the world, can be positively identified by means of the keys and descriptions given in this paper. These 35 species include all the more important British ones and seven which have not yet been recorded in Britain, viz. : Celama sorghiella (Riley), Cryptoblabes gnidiella (Mill.), Acrobasis caryae, Grote, A. juglandis (Le Baron), Etiella zinckenella (Treit.), Pyroderces rileyi (Wals.), and Anchonoma xeraula, Meyr.

The data concerning the distribution have been supplied by Dr. A. Steven Corbet and Mr. W. H. T. Tarns and are based on authentic material in the British Museum. The order in which the families and lower systematic categories are arranged in the keys and descriptions is governed only by convenience and not by phylogenetic considerations, e.g., the most primitive family, Tineidae, is dealt with last.

1. A new species of aphis, Aphis (Doralis) cognatella, found on Euonymus europaeus is described and compared with Aphis (Doralis) fabae, which it closely resembles. This new aphis is brown in colour and has long hairs.

2. Two individuals, intermediate in character between oviparae and sexuparae, are mentioned.

3. Transference experiments, carried out under somewhat artificial conditions, show that although the aphis is normally found on Euonymus sp., it can exist for some time on Rumex obtusifolius, R. crispus, Chenopodium album, Capsella bursapastoris, Arctium lappa, and Beta vulgaris (flower stalks), which are also host plants of A. fabae, but it does not colonise Vicia faba.

4. The sexuparae are apterous and produce males, oviparae and apterae, thus differing from A.fabae, in which there are two sexuparous forms, one an alate gynopara and the other an apterous form found on the summer hosts.

5. Olfactometer experiments give no indication of any olfactory response to the odour of E. europaeus leaves.

The pyrethrins, nicotine, rotenone and a derris resin have been tested in the laboratory under standard conditions for their ovicidal effect. The test-subjects were : Pieris brassicae, Plutella maculipennis, Aphis rhamni, Ephestia kühniella and Sitotroga cerealella. Notes on the technique of egg production are given for these species. In the majority of the tests made a water medium containing acetone together with sulphonated lorol as a wetting agent was used.

It has been shown that all these products are toxic to the species on which they were tested. Lauryl thiocyanate, β-butoxyβ'thiocyanodiethyl ether and 3 : 5 dinitro-o-cresol were included as substances of recognised ovicidal value for purposes of comparison.

All the above insecticides derived from plants compared favourably in their toxic action with the synthetics. In two instances during tests on eggs of Ephestia kiihniella, data were obtained enabling a satisfactory statistical comparisdn of relative potency to be made. In the first of these, the pyrethrins were found to be 8·45±1·47 times as toxic as 3 : 5 dinitro-o-cresol, while in the second the pyrethrins were found to be 2·66±0·26 times as toxic as a Derris elliptica resin (rotenone content 37–40 per cent.). It therefore appears that both the pyrethrins and the derris resin were more toxic, weight for weight, than 3 : 5 dinitro-o-cresol which is recognised as one of the most potent ovicides.

The above vegetable poisons were found to be toxic not only to eggs developing in a few days without a diapause, but also to those of Aphis rhamni, a species of overwintering egg. The tests on A. rhamni were made at the time the eggs were just starting to hatch. The same result might not have been obtained with eggs at an earlier stage of development.

Observations were made on the effect of the different insecticides on the development of the egg. This effect appeared to differ with each substance, either qualitatively or quantitatively, but within the limits of the experiment it seemed to be independent of the species of the egg.