In preparation of a key to the genera of African Pteromalidae, seven new genera and II new species are descriptionbed and illustrated, six generic and two specific names are placed in synonymy, 17 species are transferred to other genera, and notes are siven on some other species.
This paper surveys the early classical and recent literature (including 1976) on the benthos of lakes and reveals that density fluctuations of larval Chironomidae within the sediments occur frequently. The chironomid imago generally exhibits poor powers of flight and oviposition site selection. It is left to the first instar larva to disperse throughout the system and to select substrates upon which to live. Dispersal is achieved passively by wind induced water currents; larvae exhibiting adaptations for a planktonic existence by way of positive phototaxis and an ability to feed whilst in the plankton. Later instars also regularly leave the substrate under conditions of environmental deterioration. Planktonic activity also occurs in streams and rivers in the form of drift. In this case, larvae have been demonstrated to have poor powers of returning quickly to the substrate, and can be grouped in the category of """"catastrophic drift"""". Downstream drift is compensated for by upstream rheotaxis of young larvae. This planktonic behaviour enables the group to rapidly exploit new environments and to successfully colonise both temporary and intermittent habitats.
Although various insecticidal applications, including granular applications, seed-dressings and systemic foliar sprays, gave excellent control of Thrips tabaci on cotton, the yields from treated plots did not differ significantly from those from the untreated controls. Thrips control on cotton appears to be unjustified, except perhaps as a corrective application during unusually high infestations.
Tabanidae were caught in a variety of ways from different vegetation types. No statistical difference was shown in the species composition of the total seasonal catches from each locality. Differences were demonstrated between species in the distance from which female tabanids were attracted to an ox. More flies approached the ox from downwind than from upwind. A vertical visual stimulus was less effective than a horizontal one. Biases in catch composition were associated with catching method and the time of day at which catches were made. Carbon dioxide was strongly attractive for females of Philoliche zonata.
Repeated releases of adults of chelonus inanitus (L) in a cotton field were made during the summer of 1970 to study the ability of this parasitoid to hold the pest Spodoptera littoralis (Boisduval) below an economic threshold. The highest percentage parasitism recorded was 23,6%. In spite of parasitoid releases, the pest population reached above the economic threshold and the cotton field was sprayed with phosfolan; this treatment destroyed the parasitoid population and subsequently no parasitoids were recovered until late in the season, The 15 000 parasitoids which were released in the study area during four weeks did not produce reductions, in host population below the economic threshold.
Hyalonysius, a member of the lygaeid subfamily Orsillinae, was proposed by Slater (1962) for two South African species (of which one had been descriptionbed in the genus Nysius by Distant in 1904) and one West African species. Ashlock (1967), revising the generic classification of the Orsillinae, placed Hyalonysius in the tribe Orsillini. Two new species of Hyalonysius from South Africa, fumosus and gilvus, found by Slater and his group in field-work in South Africa and during a visit to the British Museum (Natural History), are descriptionbed in this paper. The first biological observations on members of the genus are also included.
A survey of 41 Karoo plantations of spineless varieties of opuntia established for stock feed, showed that Caetoblastis eaetorum has become widespread and abundant, infesting all but one of the plantations. Although also widespread, Dactylopius opuntiae was recorded in only 18 of the plantations. The effects of these introduced insects on the plants were studied for two years in two plantations by assessing damage to marked cladodes and to clad odes formed during the period. C. caetorum significantly reduced the growth of the plants while the damage caused by D. opuntiae was detectable but much less severe.
Sex ratios in orchard populations of adult codling moths, Laspeyresia pomonella (L.), were determined by sexing 16 412 pupal cases of newly emerged adult codling moths, collected at regular intervals for 10 consecutive years from marked zones on 120 unsprayed trees in a two-hectare pear orchard. There was a significant seasonal pattern in the adult sex ratios of the tri-voltine indigenous strain and highly significant differential ratios within each respective phase of the basic pattern. The overall adult female to male ratio was 0,9: I ,0. During the pre-blossom phase the ratio was 0,8: 1,0 and in the post-blossom phase of the first brood 1,3: I ,0. The overall first brood ratio was I, I: 1,0 showing that a preponderance of females emerged after the winter larval diapause. The ratios were 0,9: I ,0 and 0,7: 1,0 in favour of males in the second and third broods, respectively. The possible bearing of the seasonal pattern of differential sex ratios on interpretation of data from sex trap monitoring systems is discussed.
A technique for mass rearing the Natal fruit fly, Pterandrus rosa (Ksh.), in the laboratory, is descriptionbed. Details are given of oviposition cages and of devices which induce oviposition. Larval rearing trays are descriptionbed together with an artificial larval rearing medium comprising ingredients that are all locally obtainable, and cost 18,2 cents per kilogram.
The relation of weather to an outbreak of armyworm, Spodoptera exempta (Wlk.), which occurred during the dry season in Rhodesia, has been analysed. The results support the hypothesis that immigrant moths were borne by wind to an area of temporary convergence where eggs were deposited. Probably the moths came from infestations in moist grasslands not further north than latitude 150S in Mozambique.
Physoperinthus setosus is descriptionbed as new from Rhodesia and is associated with Fulleritermes coatoni Sands. A new record of Fulleroxenus coatoni from Rhodesia is given. The coevolution of the termitophile species associated with Fulleritermes is briefly discussed. These are the first records of both genera from Rhodesia.