Tea mite is widespread and common, and though it can cause considerable leaf damage it has not been shown to reduce yields in Uganda8; it is readily controlled by DDT-miscible liquid sprays8. The cotton red mite is of doubtful taxonomic status2'4'5, and it would seem advisable to leave it as 'the T. telarius complex'. It is widespread and common on cotton, particularly at senescence, though excessive applications of DDT can cause severe attacks and complete defoliation6. Eotetranychus sp. is a new record for cotton in Uganda. It was first discovered at Kawanda Research Station early in 1961 and afterwards at widely scattered sites over the whole country. It may be a potential new pest or it may be that an exceptionally wet growing season provided a suitable breeding environment. In view of the possibility of an increase in green mite and the fact that it can occur on the same plant as red mite it was decided to work out a joint control. Coaker6 showed that 0-05 per cent parathion and 0-025 per cent 'Aramite' gave good control of the T. telarius complex in Uganda and McKinlay7 that both 'Rogor' and 'Metasystox' at 0-0125 pep cent gave good control in Tanganyika. Field application of 0-0125 per cent 'Rogor' at ten-day intervals does not give satisfactory control in Uganda but 0-06 per cent does (unpublished work).Cotton leaves infested with both red and green mite were maintained in the laboratory with their petioles dipped in water. Active stages of both tetranychids were dead or dying within 4 h of spraying with 0-1, 0-05 or 0-025 per cent 'Rogor', while tea mites, which were also present on the leaves, remained perfectly healthy. Larvae of both red and green mite hatching after 24 h were killed, but those after 48 h lived and fully re-established the colony after a week. A further trial was laid down using leaves infestedwith all three species of mites in which 1 per cent DDT-miscible liquid, 0-02 per cent 'Rogor'-emulsifiable concentrate and a mixture of both 1 per cent DDT and 0-02 per cent 'Rogor' were sprayed on to either the upper side or the lower side of the leaves only. The 1 per cent DDT m.l. applied to the lower sides of the cotton leaves killed the active and the quiescent stages of all three species of mites; tea mite disappeared completely within 4 h while the tetranychids remained twitching on their webs for days before finally dying. Healthy larvae of all three species re-appeared within 4 days and the colonies were re-established within 8 days. The same spray applied to only the upper surface of the leaves gradually reduced the numbers of actively wandering tea mites but had no effect on either red or "green mite. The 0-02 per cent 'Rogor' applied to either surface had no effect on tea mite. Applied to the lower leaf surface it killed both red and green mite within 4 h and hatching larvae died over the following 2 days but after 4 days there were no visible toxic effects. 'Rogor5 sprayed on to the upper surface only had no effect on red or green mite living on the underside of the leaf and so cannot be absorbed by the cotton leaf under these conditions. With the mixture of DDT and 'Rogor', all three species were dead within 2 h, and no living larvae were seen until the fourth day and re-establishment of the colonies was delayed until the twelfth day. The same mixture applied to the upper leaf surface gradually reduced the tea mite numbers, but the tetranychids increased. On the control leaves both the red and green mite numbers increased continuously but the tea mite population gradually decreased, as they either died naturally or wandered off the leaves. It was interesting to note that a large, active, predatory mite, as yet unidentified, was unaffected by either insecticide. After observing the failure of 'Rogor', a known systemic insecticide, to kill red or green mite living on the underside of the leaves when applied to the upper, another trial was laid down in which unsprayed leaves had their petioles dipped into 'Rogor' instead of water. 0-1 and 0-05 per cent 'Rogor' were used and within 24 h both red and green mite were dead but tea mite was still alive. 'Rogor' absorbed into the leaves in this way proved to be highly phytotoxic and within three days all the treated leaves were dead or dying.It is concluded that 0-02 per cent 'Rogor' as an underleaf spray is an effective contact poison against red mites of the T. telarius complex and green mite, Eotetranychus sp. nr. deflexus, but that it does not appear to be absorbed by the cotton leaf when sprayed on to the surface. 'Rogor', even as strong as 0-1 per cent, has no effect on tea mite, H. latus. A good wetting spray of 1 per cent DDT is a slow-killing poison to both red and green mite and is extremely lethal to tea mite. The residual toxicity appears to be no more than 4 days for either insecticide under the conditions of the experiment. There is no evidence of either toxicant having any action on the eggs of any of the three mite species. A good field control should be obtained with a mixture of 1 per cent DDT m.l. and 0-02 per cent 'Rogor' e.l. applied as an 'up and under' spray, but from the laboratory evidence a second application would be required about 12 days later. I thank the Commonwealth Institute of Entomology for its help in identifying the Eotetranychus species.