Rice tungo virus is tranmitted by Nephotettix impicticeps Ishihara but not by the closely related N. apicalis (Motsch.). Hybrids have been obtained from crosses between these two species. The morphological characteristics of the hybrids were not identical with either parent in respect to the marking on the abdomen of the nymphs, the submarginal black band on the vertex of the adults, or the number of teeth on the ventral surface of the aedeagus of the male genitalia. However, more than 10 per cent. of them, regardless of stage of development or sex, were able to transmit the tungo virus, indicating that the transmissive ability is inherited even in an interspecific cross. The virus seems to be nonpersistent in the hybrids as it is in N. impicticeps.

Analysis of the results obtained from suction-trap catches of the coffee leaf-miners, Leucoptera meyricki Ghesq. and L. caffeina Wshbn. on an unsprayed block of coffee at the Coffee Eesearch Station, Lyamungu, on the slopes of Kilimanjaro, are given.

By thermal summation methods it was possible to delimit successive generations of moths with some degree of accuracy and the generation catches were used for regression analysis with various meteorological factors. With L. meyricki, a negative correlation was shown between the rate of increase from one generation to the next and with both maximum and mean daily temperature, solar radiation and duration of sunshine taken as means over the period of each generation. In each case, the highest degree of correlation was found between the meteorological data in one generation and the rate of increase in the next.

When the generation catches were plotted on a logarithmic scale it was found that linear regression lines could be fitted to the periods of both rise and fall of the annual outbreak. With L. meyricki, the rate of increase of the rise was negatively correlated with, and the rate of decrease of the fall positively correlated with, the size of the generation present at the beginning of the outbreak. It is therefore possible, knowing the size of the minimum generation, to predict the size of the coming outbreak. No such relationship could be proved with L. caffeina, probably because the catches of the key generations were very small, but when the catches of the two species were pooled the same relationship held. It is probable that parasites are the main factor governing the annual fluctuations.

A method for continuously rearing cabbage root fly, Erioischia brassicae (Bch.) is described.

Adult flies fed on sucrose, brewers’ yeast and yeast hydrolysate laid an average of 220 eggs per female when caged together in large numbers and 376 eggs per female when caged singly. Egg viability was 86 per cent. Egg hatch was severely reduced by relative humidities of less than 90 per cent, and the embryo became more susceptible to desiccation as it matured. The larvae were reared on swede, and maximum survival was obtained when the swedes were inoculated with an optimum number of eggs calculated from the ratio of 1 egg: 1.6 g. of swede. Different ratios were obtained from turnip and winter radish indicating that survival was probably related to the nutritional value of the rearing medium as well as to its availability. An average of 68 per cent, of the eggs placed on swede produced pupae that were equivalent in size to wild pupae. The fecundity of the flies was directly related to pupal weight and to the availability of protein in their diet. Adult longevity was reduced more by mutual disturbance than by any other factor.

A life-table and age-specific fecundity schedule are given for females of Glossina austeni Newst. maintained on lop-eared rabbits. From these the innate capacity for increase in numbers (τm) is calculated, from two sets of data, as 0.0166 and 0.0155 per day, respectively. These values are better than previously obtained for Glossina and it is concluded that as such they were mainly due to the excellent nutrition of the flies. A colony in which all female offspring produced are added to the breeding stock is referred to as being in the ‘expanding phase’. The stable age distribution that would be established in a rabbit-fed colony of G. austeni in the expanding phase and the expected rate of increase in numbers of the colony when the stable age distribution exists are calculated from the value of τm.

The characteristics of a colony of G. austeni in the ‘stationary phase’, when only those offspring required to maintain the colony at a constant size are retained, are described. It is concludef that a stationary colony of y adult flies would have a disposable output per week of 0.277y young adult males and 0.233y young adult females. Some implications of these findings in relation to the sterible male techinque for tsetse control are briefly discussed.

A new type of olfactometer was designed to study the responses of mosquitos to various stimuli. Hosts could be displayed downwind as well as upwind from the mosquitos, and two hosts could be displayed simultaneously, one upwind from the other. Responses to radiations, if any, and to odours could be measured.

Mosquitos were not attracted downwind to an arm displayed within 61 cm., even when they were stimulated by CO2 (under an incident illumination of about 10 foot-candles). About half the mosquitos showed a positive anemotactic response (i.e., they left the end downwind compartment in which they were released) in a current of room air, which undoubtedly contained human emanations. Only 15 per cent, responded to filtered air. Carbon dioxide caused no increase in response to filtered air but increased the number responding to room air (76 per cent, left the end down-wind compartment). Equal numbers of mosquitos responded to an arm displayed upwind in room air and in filtered air, i.e., about 83 per cent, left the end compartment. Carbon dioxide caused no increase in the number of mosquitos responding to an arm but increased the number responding to attenuated emanations from an arm. A repellent (deet) eliminated most of the response to an arm; the addition of carbon dioxide increased upwind flight to the treated arm, but many of the mosquitos flew past it. Carbon dioxide therefore appears to have a synergistic action with arm odours in the attraction of females of Aedes aegypti (L.). However, this conclusion does not exclude other behavioural effects of carbon dioxide demonstrated by other investigators.

Eesponses to arms in this new type of olfactometer were nearly identical to those obtained in another type previously used in a large-scale study. The testing confirmed earlier reports that mosquitos do not fly far in the same direction as wind-current and that host location was not possible through positive anemotaxis in the absence of light. Mosquitos were not attracted to a source of infra-red radiation.

The new direct method of comparing the attractiveness of different subjects demonstrated that mosquitos would leave the vicinity of one arm and migrate further upwind to another that was more attractive. Water and acetone rinses of human arms reduced attraction; acetone appeared to be a better solvent for the attractant substance than water.

The taxonomic status of the Culex vishnui group of species is discussed. Three species belonging to this group, C. vishnui Theo., C. pseudovishnui Colless and C. tritaeniorhynchus Giles, were recognised in the study area near Vellore, South India. All three species are described on the basis of adults and larvae, and keys for the identification of adults are provided.

It is likely that under some conditions apterous aphids are significantly involved in the spread of plant viruses, most importantly by walking across soil from plant to plant. Various factors which affect their importance are considered in the paper.

Figures are given for the frequency of movement of apterae of Myzus persicae (Sulz.) under settled conditions; this was found to vary with the species of host-plant that the aphid was on.

Eourth-instar and adult apterae can walk proficiently on soil. The effect of soil condition on this is described. The walking speed of adult apterae on soil is 5.2 cm./min. at 18°C, and 1.2 cm./min. at 8.5°C. The walking speed of fourth-instar aphids on soil is 3.2 cm./min. at 18°C.

Experiments showed that walking aphids are well able to locate a new host-plant, and that the attraction is visual.

The significance of these observations is discussed, and it is concluded that apterae have a greater potential as virus vectors than has been generally realised.