The third-stage larva of Chalcosoma atlas (L.) collected in Malaysia is described, with illustrations, and a key is provided to distinguish larvae of this species from those of Oryctes rhinoceros (L.) and Xylotrupes gideon beckeri Schaufuss, all of which occur in similar breeding sites.

The eggs, three larval instars and puparia of Chrysomya bezziana Villeneuve are described and illustrated in detail by scanning electron micrographs. Particular attention is paid to the extent and nature of the median strip in the eggs and the spine bands and spiracular structures in the larvae and puparia.

Eggs and third-instar larvae of five other species of Chrysomya, C. nigripes Aubertin, C. varipes (Macquart), C. rufifacies (Macquart), C. saffranea (Bigot) and C. megacephala (F.), are illustrated, described and compared with C. bezziana and each other by means of keys, which also permit their identification. In addition, notes on the puparia of these species are provided.

Ingestion of radiolabelled plant juices from cut surfaces of leaves during foraging and during substrate preparation for the fungus garden was demonstrated for laboratory colonies of the leaf-cutting ants Atta cephalotes (L.) and Acromyrmex octospinosus (Reich). Using P32 isotope, up to one-third of the radioactivity in the leaves was taken in directly by the colony as a whole, but this was much less when C14 was used. Additional plant material was taken in by the ants via the fungus garden. Large numbers of ants spend time in investigating cut surfaces of leaves and also in cutting and crimping leaves. Ingestion of plant material during these processes could play an important nutritional role in the colony and this may explain why many ants return from foraging apparently unladen. Large ants obtained most of their plant juice intake during foraging and the medium and small ants took much of theirs during substrate preparation. Inhibitory chemicals did not affect cutting but they reduced drinking and also reduced the intake of P32 from leaves during substrate preparation. The ants also ingested different amounts of P32 from leaves of different acceptability. It is suggested that leaf-cutting ants use fungus culture as a means of ‘sidestepping’ plant inhibitors. Nutrients are ingested directly from leaves when these are palatable, and the less palatable components are made available to the ants via the fungus.

The female sex pheromone gland of Diparopsis castanea Hmps. consists of modified intersegmental tissue between the eighth and ninth abdominal segments. Glands contain an average of 12·73 ×10–3 μg of pheromone consisting of 80·4±2·0% trans-9, 11-dodecadien-l-yl acetate (range 72·7–86·7%) and 19·6±2·0% 11-dodecen-l-yl acetate (range 13·3–27·3%). Although no significant correlation exists between female body weight and pheromone content of the gland, the duration of sex pheromone release over the lifespan of a female is positively correlated with its weight on emergence. Six behavioural steps may be recognised in the precopulatory behaviour of females but the frequency and duration of sex pheromone release is strongly influenced by both temperature and light intensity. At 25°C females typically ‘call’ on two or more occasions for 41–50% of the night, calling commencing earlier at cool (13·4°C) temperatures than at moderate (19·4°C) or warm (25·0°C) temperatures. Calling by mated females increases considerably from four to five nights after mating but is typically of shorter duration than for virgins. The dispersal flight of Diparopsis males in cotton crops commences almost immediately after sunset and before the end of dusk, with peak male catches in sex pheromone traps occurring earlier in the cooler months of May and June (20.00–22.00 h) than in November (02.00–04.00 h). The Diparopsis synthetic sex pheromone, dicastalure, traps a greater proportion of males and females both earlier and later in the night than virgin females and this ‘timing advantage’ may be important in a pheromone control programme based on disruption of communication between the sexes.

The synthetic sex pheromone of Diparopsis castanea Hmps., dicastalure, is a 4:1 synergistic combination of 93% trans:7% cis-9,11-dodecadien-1-yl acetate (IV) and the unattractive compound 11-dodecen-1-yl acetate (IIB). Both cis and trans-9-dodecen-1-yl acetate (IIA), the latter occurring in the female pheromone gland, are potent inhibitors of male attraction, as little as 10–4 mg IIA significantly reducing the attractiveness of virgin females in pheromone traps for more than one month in the field. Inhibition is typically close range, although higher concentrations are inhibitory when placed at up to 1 m from the female. IV and IIB also reduce male catch in female-baited traps, but dicastalure does not. Recently mated females, confined with virgins, reduce male catch, thereby indicating release of an unknown inhibitor. When formulated in a suitable extender, such as corn-oil, dicastalure may be released from sealed polyethylene vials or from cellulose acetate cigarette filters, and inclusion of the antioxidant 2:6-di-tort-butyl-p-cresol (BHT) prolongs the attractiveness of 1 mg dicastalure formulations beyond 25–30 days. Release from polyethylene is more efficient than from either polypropylene or cellulose and moth catch over a five-week period is linearly related to the logarithm of pheromone concentration. Significant communication disruption, as measured by reduced trap catches of male Diparopsis, occurred when female-baited traps in 100 m2 cotton plots were surrounded by point sources of either dicastalure (synthetic females) or the inhibitory IIA acetate (anti-females). Since dicastalure is occasionally less attractive than virgin females, efforts are being made to improve pheromone slow release formulations.

The synthetic sex attractant of the pink bollworm of cotton, Pectinophora gossypiella (Saund.) (Lepidoptera, Gelechiidae), is a mixture of (Z, Z) and (Z, E)-7, 11-hexadecadien-l-ol acetate, referred to as gossyplure (Hummel et al., 1973). Field trials in the Lower Shire Valley, Malawi, have shown that of various mixtures tested, 55–60% of the (Z,Z) isomer in a mixture of the two acetates gives maximum field attraction. The catches of both pink bollworm males and males of the red bollworm of cotton, Diparopsis castanea Hmps., in pheromone traps are not affected by the release of mixtures of the pheromones of both species together. Dual-purpose sex pheromone traps may therefore be used to monitor both pest species at the same time. A simple omnidirectional flat disc trap is as efficient in trapping pink bollworm males as more complex designs. Release of gossyplure from a sealed 2·5 ml polyethylene vial or from a Zoecon beem-polyethylene vial is more efficient than from narrow-bore teflon capillary. Presence of the antioxidant 2,6-di-tert-butyl-P-cresol at 8·4% w/w gossyplure does not increase the attractive life of the pheromone in the field. Considerable numbers of the Angoumois grain moth Sitotroga cerealella (Ol.) (Tineidae), together with a new species of gelechiid, were occasionally caught by gossyplure lures in cotton fields. Catches of pink bollworm are not influenced by moonlight or trap colour but are significantly influenced by trap area. Maximum catches of males occur between midnight and 04.00 h in June and between 01.00 and 05.00 h in August.

The synthetic sex pheromone (dicastalure) of the red bollworm of cotton, Diparopsis castanea Hmps., in Central and Southern Africa, and an inhibitor of male sexual attraction (trans-9-dodecenyl acetate,=IIA), were used in an enclosed 0·2 ha cotton field-cage to reduce successful female matings. Over one month dicastalure at 21·0 and 42·3 g/ha produced average reductions in mating of 47·9% and 72·5% respectively and 37·9 g IIA/ha produced an overall reduction in mating of 71·5%, or 79·5% in released moth populations, over the same period. The proportion of virgin females present in disruption situations was significantly greater than in untreated populations and was density-independent for moth populations of up to 2 200/ha. The proportion of fertile eggs in disruption situations was correspondingly reduced to 30·2% from an average of 67·9% in control cycles. Reduction in sex pheromone trap catches is an unsatisfactory indicator of the extent to which males are prevented from inseminating females and considerably over-estimates the true degree of disruption. This is the first time that a naturally occurring inhibitor has been used successfully to disrupt mating in a field population of insects and it indicates the potential of the method for the control of high density pest populations in cotton. However, use of polyethylene dispensing mechanisms similar to those used in the field-cage disruption experiments would be unsuitable as a practical method of dispensing behaviour modifying chemicals and it is suggested that, for suitably controlled release of such chemicals, currently available microencapsulation technology offers the best prospects.

Variation in temperature affected the developmental periods of eggs, larvae and nymphs of Rhipicephalus appendiculatus Neum. and developmental periods were shortest at an optimum of 30°C. The periods increased as temperatures diverged from the optimum until upper and lower temperature limits were reached, when metabolism ceased. These limits were 16°C and 34°C for eggs, and 12°C and 41°C for larvae and nymphs.

Generally, relative humidity did not affect the rate of development. It did, however, critically affect survival, particularly of eggs and larvae. The relative humidity range of 60–70% was critical, and below this range survival of the eggs and larvae was very limited. Nymphs and adults were more resistant, and natural tick populations probably survive hot and dry seasons in these stages.

It was found that in a habitat with thick vegetation, temperature and humidity fluctuations were smaller than in one with sparse vegetation, and the former therefore supported a greater tick population. Denying cattle access to this thick vegetation or getting rid of it altogether seem to be possible methods of reducing the tick load of cattle in the area studied.

Only a very strong dose of 0·5 mg of hempa caused necrosis in testes of Locusta migratoria (L.). The apical cells, spermatogonia and primary spermatocytes became pycnotic and the germ cells were disorganised. Multinucleated cells also developed, due to failure of spindle formation, and a few hypertrophied spermatids occurred. In ovaries the chromatin of the follicular epithelial cell nuclei was abnormally fragmented; nuclei of the follicular epithelial cells became pycnotic; germinal vesicle was badly damaged; cytoplasm of the follicular epithelial cells was drawn into the peripheral empty space formed by the contraction of the ooplasm; the follicular epithelium degenerated later; and yolk formation was inhibited. With increased doses and post-treatment periods necrosis became more marked. Hempa was more effective in the ovary than in the testes of L. migratoria.

Three plant spacings, 30 cm, 7·5 cm and 2·5 cm within rows 90 cm apart, equivalent to about 36, 143 and 430 thousand plants/ha respectively, were used in three field trials on the population dynamics of Aphis craccivora Koch on groundnuts at Chitedze, Malawi in 1964–1967. Aphid density per infested plant was consistently higher, while numbers of aphid-infested plants per unit area were consistently lower, in 30 cm than in 2·5 cm spacing. Aphid numbers per unit area increased to similar levels at all spacings in crops under 40–50 days old, but subsequently aphid density was consistently lower in 2·5 cm than in 30 cm spacing. This effect could not be related to the intensity of fungus disease infection, parasitism, predation, the availability of feeding sites or the rate of emigration. Aphid groups were, however, consistently smaller in 2·5 cm than in 30 cm spacing in one trial. The potential rate of increase was studied in two trials using the methods of Hughes (1962), and was found to be consistently lower in 2·5 cm than in 30 cm spacing. The rate of plant growth was relatively depressed in 2·5 cm spacing, particularly after 40 days. The effect of spacing on aphid numbers was attributed to the effect of host-plant condition on the potential rate of increase.

In two trials, at Chitedze, Malawi, in 1966–1967, the spread of rosette virus disease in groundnuts (Arachis hypogaea) intersown with field beans (Phaseolus vulgaris) was less than the spread in groundnut monocultures comprising plant populations equivalent to the number of groundnut plants and to the total number of plants in the intersown crop. In one trial, numbers of early rosette transmissions were related to numbers of alate Aphis craccivora Koch, the vector of the virus, found on groundnut plants. Immigrant alate A. craccivora settling on the intersown crop were trapped by the hooked epidermal hairs of the bean plants and the observed reduction of rosette infection in the intersown crop was attributed to this effect. Inter-sowing with beans is considered less effective than early-sown, high-density monoculture as a method of reducing groundnut rosette infections and yields of groundnuts from inter-sown crops may be lower than those obtained from high-density monoculture.

Communication between adult male and female Spodoptera littoralis (Boisd.) was disrupted by spraying microencapsulated formulations of pheromone inhibitor (IIA) (Z)-9-tetradecen-1-yl-acetate on lucerne plots in north-west Crete. Polyurea-based microcapsules applied at the rate of 100 g/ha active ingredient caused a 97% disruption for a period of seven days, as measured by the reduction of catches in the treated area in traps baited with the pheromone attractant (III) (Z)-9, (E)-11-tetradecadien-1-yl acetate, compared with catches in control areas. At lower rates of application both the level of disruption after seven days and the subsequent persistence of the effect were reduced. When applied at a rate of 100 g/ha active ingredient, disruption of 80% and above was achieved for a period of three weeks. Slower release microcapsules containing IIA based on polyurea/polyamide appeared more effective in that a level of disruption was achieved at one-tenth the amount of active ingredient required for the polyurea-based formulations.

III dispensed in polythene vials caused 97% disruption when distributed at the rate of one vial per 9 m2, with lower levels of disruption at distributions of one vial per 25 m2 or 50 m2. IIA was much less effective in causing communication disruption at the same rates of distribution and no clear dose/response relationship was established.

Inside enclosures of 10 100 and 1 000 m2 fenced by single-strand polythene impregnated with IIA at the rate of 1 mg/5 cm and maintained at a height of 0·5 m, a high level of disruption in excess of 93% was achieved for the first five days. The effect persisted in the smaller enclosures in that disruption in excess of 80% was maintained for a period of 40 days. In the 1 000 m2 enclosure the effect declined much more quickly.

When IIA and III were dispensed together in WT traps the inhibitory effect persisted for at least 60 days. Similarly the polyurea-based microcapsules containing IIA together with III in WT traps maintained an inhibitory action for periods of 30–40 days. Polyurea/polyamide formulations of IIA were generally less effective, probably because loss from these slow releasing formulations became too low. Small numbers of mostly unmated female moths were attracted to the traps when IIA was exposed together with III, either when dispensed in the polythene vials or in microencapsulated formulations.

In this survey of distribution and prevalence of adult ticks (Acarina, Ixodoidea) parasitising domestic animals in the northern regions of the Somali Democratic Republic, 26 species were identified. The ten most common species were widely distributed with Hyalomma anatolicum anatolicum Koch, H. dromedarii Koch, H. erythraeum Tonelli-Rondelli, H. impeltatum Schulze & Schlottke and Rhipicephalus sanguineus group more common in the drier vegetation zones, and H. marginatum rufipes Koch, H. truncatum Koch, R. e. evertsi Neum., R. pravus Dön. and R. pulchellus (Gerst.) more common in the wetter woodland, evergreen and forested zones. Four species, Amblyomma gemma Dön., A. variegatum (F.), Boophilus decoloratus Koch and R. simus Koch, were confined to the wooded zones above 1200 m altitude. Species collected less frequently were Argas persicus (Oken), Amblyomma falsomarmoreum Tonelli-Rondelli, H. anatolicum excavatum Koch, H. m. marginatum Koch, H. m. turanicum Pom., H. punt Hoogst., Kaiser & Pedersen, Ornithodoros savignyi (Aud.), R. armatus Pocock and R. longicoxatus Neum. Ambylomma lepidum Dön. was represented only by a few specimens introduced on nomadic livestock.

Nearly 60% of the total number of ticks collected were R. pulchellus. This species is considered to be the main vector of Nairobi sheep disease (NSD) virus in northern Somalia. NSD is the most important tickborne disease in sheep and goats and causes considerable economic losses to the Somali livestock industry. A. gemma and A. variegatum are probably the vectors of Cowdria ruminantium (heartwater) in sheep and goats in the western highlands. These two ticks are also incriminated in the spread of Dermatophilus congolensis infection (streptothricosis). R. e. evertsi may be the vector of Babesia motasi in sheep and goats. Boophilus decoloratus is probably the vector of Babesia bigemina in cattle in the western highlands. Various tick species may be associated with bacterial abscesses of feet and lymph nodes in sheep and goats.

Indigenous cattle are trekked, along well defined routes, from the north of Nigeria to markets in the south of the country. A major route crosses the River Niger at Jebba and proceeds south through Ilorin, Ogbomosho and Oyo towns. In 1912 the tsetse fly Glossina morsitans submorsitans Newst. was absent from this route south of Jebba. The species appeared mid-way between Jebba and Ilorin in about 1935, reached Ilorin by about 1950 and Oyo by, or before, 1967. The rate of southwards advance, if linear, was about 5·4 km per year or 104 m per week.

The Jebba-Oyo infestation may have originated, not as a southwards extension of a fly belt north of the River Niger at Jebba (now termed Belt 24), as generally believed, but by immigration of flies from Eastern Ilorin Province, known to be heavily infested as early as 1912. Several cattle routes from that area converged north of Ilorin before the present route became predominant.

G. m. submorsitans was eradicated from the route south of Ogbomosho by insecticide spraying in January 1970. The rate of re-invasion of this section was measured for the next three years and found to be about 5·13 km per year or 99 m per week, proceeding faster during dry than during wet seasons.

The calculated rates of advance, both long and short term, were about half the figure (180 m per week) proposed by other workers as the dispersal rate of individual flies, which is believed to determine rates of advance. The relative slowness of the present advance was probably related to the equability of the climate, in which seasonal increases and decreases in fly population were slight.