The four significant pest species in the Helicoverpa genus (H. armigera, H. assulta, H. punctigera and H. zea) are morphologically similar and can only be reliably distinguished through dissection of adult genitalia. Two partial regions of the mitochondrial DNA (mtDNA), the cytochrome oxidase subunit I (COI) and the cytochrome b (Cyt b) genes were amplified by PCR and digested with restriction endonucleases. The restriction patterns, generated by the endonucleases BstZ17I and HphI, demonstrated reliable differentiation of the four Helicoverpa pest species. This technique is fast, reliable and effective at distinguishing specimens irrespective of their life stages and offers support to conventional taxonomic differentiation based on morphological characters.

Termites were sampled using randomized soil pits in 64 cropping plots, each 25 x 25 m, forming an experimental agrisilvicultural system in both a 6- and an 18-year-old Terminalia ivorensis plantation, in which canopy cover, crop, cropping system and land preparation were the principal treatment variables. The treatments were established in April 1995 and sampling was carried out in November 1995, February 1996 and July 1996. A total of 82 termite species were found, of which 67 were soil-feeders. Overall termite abundance and the abundance of soil-feeders increased between November 1995 and July 1996, reaching a mean of nearly 6000 m-2. Pooling termite data from these sampling dates, in the old plantation, the high canopy cover treatment (192 stems ha-1) had a greater abundance of termites, compared with the low canopy cover treatment (64 stems ha-1) and this effect was independent of crop type (plantain or cocoyam), cropping system (single stands or mixed crops) and land preparation (mulch retained or burned, plantain only). The young tree plantation (same tree densities as in the old plantation) showed no significant difference in termite abundance between high and low canopy (levels of tree foliage) densities, though the high canopy sheltered a greater number of termites. Analysis of covariance showed that crop yield (both plantain and cocoyam) was not directly linked to the abundance of all termite populations, but that the cocoyam yield was positively correlated with the abundance of soil-feeding termites (the majority in the assemblage) in the young plantation. This may be due to the beneficial conditioning of soil resulting from the foraging and construction activities of soil-feeders.

The mealybug Maconellicoccus hirsutus (Green) occurs in many tropical and subtropical parts of the Old World and extends into some temperate areas. It has now reached the West Indies where it is causing extensive damage to plants. There is concern that it may be introduced to the southern USA and to Central and South America. A brief account is given of reported damage caused by M. hirsutus to some commercial and food crops in Asia and Africa and the species is redescribed. M. multipori (Takahashi), now known from a wide area in southern Asia, is redescribed, and M. ramchensissp. n. from Nepal, is described as new. These two species are closely related to M. hirsutus and can easily be mistaken for it. M. hirsutus and M. multipori are sometimes intercepted at quarantine inspection of plants and plant produce in the USA and Europe. In order to aid identification, a key is provided to the eight species presently included in the genus Maconellicoccus Ezzat.

Based on previous studies of the trap-orientated behaviour of Diptera, a variety of new traps was designed to maximise the speed and probability of capturing Glossina morsitans morsitans Westw. and G. pallidipes Aust. arriving near traps, and to minimise the probability of capturing other flies. In Zimbabwe, catches were made with these traps in the presence and absence of carbon dioxide and acetone as odour attractants, leading to the identification of a simple trap for which the probability of capturing Glossina spp. was up to twice as great as it was for a standard biconi-cal trap, and for which the probability of capturing other Diptera was very much less than it was for the biconical trap. The probability of capture by the simple trap was 100% for G. pallidipes, 51% for G. m. morsitans, 6% for Stomoxyinae and 1% for non-biting Muscidae. Half the tsetse that arrived near the simple trap were captured within 5 min of arrival. The number of tsetse that contacted simple targets designed to expose flies to insecticide amounted to 32–263% of the catches of a biconical trap. The use of traps and targets for tsetse control, and the procedures for trap improvement, are discussed.

The Seasonal Factor.

1. The period of stress due to extreme climatic conditions is far shorter in the forest than in the meadow-pan.

2. G. tachinoides is primarily dependent upon riverine vegetation or residual forest, and has only a very limited wet season spread. G. submorsitans is primarily an open woodland fly with great powers of dispersal which are annually checked by adverse climate that enforces a temporary dependence upon the riverine forests.

3. G. tachinoides abounds within the stream-bed or residual forest ; G. submorsitans abounds on the forest fringe.

4. The dispersal of both species is closely associated with evaporation and saturation deficiency. A mean monthly evaporation of 20–28 cc. and a saturation deficiency of 5 to 8 millibars results in maximal dispersal ; dispersal yields to concentration as the evaporative power of the air increases above these zones.

5. The extent of the annual dispersal is indirectly governed by the duration of the wet season—the longer the season the more extensive the dispersal.

6. The population of G. submorsitans steadily increases throughout the rains as the evaporation falls, and becomes maximal towards the end when the evaporation is in the optimum zone (20—25 cc.) ; density steadily falls throughout the dry season as evaporation rises, and becomes minimal at the end when evaporation is maximal. G. tachinoides is believed to behave similarly, but the optimum zone of evaporation is probably about 6 to 10 cc.

Aphids are, arguably, the single most damaging group of agricultural insect pests throughout the world. Plant tolerance, which is a plant response to an insect pest, is viewed as an excellent management strategy. Developing testable hypotheses based on genome-wide and more focused methods will help in understanding the molecular underpinnings of plant tolerance to aphid herbivory. As a first step in this process, we undertook transcript profiling with Affymetrix GeneChip Barley Genome arrays using RNA extracted from tissues of tolerant and susceptible genotypes collected at three hours, three days and six days after Diuraphis noxia introduction. Acquired data were compared to identify changes unique to the tolerant barley at each harvest date. Transcript abundance of 4086 genes was differentially changed over the three harvest dates in tolerant and susceptible barley in response to D. noxia feeding. Across the three harvest dates, the greatest number of genes was differentially expressed in both barleys at three days after aphid introduction. A total of 909 genes showed significant levels of change in the tolerant barley in response to D. noxia feeding as compared to susceptible plants infested with aphids. Many of these genes could be assigned to specific metabolic categories, including several associated with plant defense and scavenging of reactive oxygen species (ROS). Interestingly, two peroxidase genes, designated HvPRXA1 and HvPRXA2, were up-regulated to a greater degree in response to D. noxia feeding on tolerant barley plants, indicating that specific peroxidases could be important for the tolerance process. These findings suggest that the ability to elevate and sustain levels of ROS-scavenging enzymes could play an important role in the tolerant response.

Busseola fusca (Fuller) is a serious pest of maize and sorghum in Tanganyika where it occurs mainly at altitudes of 4,000 ft. and over.

Laboratory work on the life-cycle and on the diapause of the larva is described. Diapause is terminated by contact with water.

Field work at Nzega, Western Province, indicates that the first sowings, made within two to three weeks of the beginning of the rains, are likely to be heavily attacked by larvae of the first generation. These are the progeny of a “raininduced” flight of adults of Busseola derived from diapause larvae in the maize and sorghum left in the fields from the previous season, the larvae being induced to pupate when the stems are wetted by rain.

The number of generations in the main crop season, November–June/July, is two. A third generation occurs in sorghum tillers produced after June/July.

No alternate hosts of importance comparable with maize and sorghum have been found.

Cultural control by burning the crop residues left in the field after harvest, in order to destroy the diapause larvae, is not practicable in peasant agriculture as these residues are required for such purposes as palisading, building of contour banks and for grazing cattle and goats during the dry season.

Chemical control of the first generation of Busseola in young maize can be achieved by the application of a dust containing 2·5 per cent. DDT into the funnel of the plant. In 13 experiments on peasant-owned plots at Mbeya, in which a dust containing 2·5 per cent. DDT was applied four times, at weekly intervals, beginning about 18 days after germination, and at the rate of 10 lb. per acre, the average weight of maize cobs from 100 plants was increased from 12·46 to 22·82 kg., an increase of 83·1±19·0 per cent. Factors other than Busseola which affect the yield are discussed and it is suggested that control measures would probably be worthwhile only where a combination of a suitably fertile soil, early planting and adequately distributed rainfall obtains.

The influence of green ants, Oecophylla smaragdina (Fabricius), on insect pests of cashew, Anacardium occidentale Linnaeus, in tropical northern Australia was investigated using field surveys and field observations. Oecophylla smaragdina was abundant in the native vegetation of the area, and it was a dominant predator when found in cashew plantations. Oecophylla smaragdina significantly reduced the numbers of the four most important species of insect pests (Helopeltis pernicialis Stonedahl, Malipatil & Houston, Penicillaria jocosatrix (Guenée), Amblypelta lutescens (Distant) and Anigraea ochrobasis Hampson) on cashew trees, and trees with higher numbers of O. smaragdina produced higher quality nuts than trees with fewer numbers of O. smaragdina. Other ant species also reduced pest numbers, but not as much as O. smaragdina. The possibility of using O. smaragdina to control insect pests of cashew in the future is discussed.

The performance of eighteen clones of Myzus persicae (Sulzer) on pepper and tobacco plants at 20°C and L16:D8 and the choice of young adult apterae between tobacco and pepper leaf-discs were examined. The clones were collected from weeds and peach in two tobacco-growing regions: Katerini, northern Greece and Karditsa, central Greece (only from weeds) and from Lehonia, central eastern Greece where tobacco is not cultivated. All clones did well on both hosts. However, the analysis of data revealed a significant effect of ‘region / host plant origin’ on aphid performance. The mean values of adult weight, intrinsic rate of increase and fecundity of the clones collected in Lehonia and reared on tobacco were significantly lower than the observed values for clones from Katerini and Karditsa. Aphids from Lehonia had significantly higher mean values for developmental time on tobacco than clones from the other regions whereas the opposite was observed when aphids were reared on pepper. Aphids collected in Lehonia performed better on pepper than those originating from the tobacco-growing regions. A choice test revealed differences among the clones originating from different regions. Fifty three percent and 43% of aphids from weeds and peach from Lehonia, respectively, chose pepper. By comparison 41.5% and 40.0% of aphids from peach and weeds from Katerini, respectively and 49.5% of aphids from Karditsa preferred tobacco. The results are discussed in relation to host specialization in M. persicae.

The well-established carboxylesterase-based resistance to insecticides in Myzus persicae Sulzer has recently been accentuated by the appearance of aphids with a modified acetylcholinesterase (MACE) insensitive to pirimicarb and the novel aphicide, triazamate. This target site resistance mechanism was found in M. persicae from crops in the UK for the first time in 1996, together with especially large proportions of aphids with R2 and R3 levels of carboxylesterases, a combination that was associated with serious insecticide failures. This paper describes the incidence of both mechanisms and discusses the implications for future recommendations for aphid control in the UK.

Culicoides variipennis sonorensis Wirth & Jones and C. nubeculosus (Meigen) were orally infected with African horse sickness virus (AHSV) type 9 and subsequently incubated at 10, 15, 20 and 25°C (R.H. 80%±10%). A time course of infection rates and virus titres was recorded by assaying flies individually or in pools, and survival rates of flies were also estimated. Survival rates at 10, 15 and 20°C were very similar and 80–90% of flies remained alive after 14 days; at 25°C after the same period survival was reduced to 40%. None of the C. nubeculosus became persistently infected with AHSV, but the virus took longer to clear as the incubation temperature dropped. At temperatures of 10, 15, 20 and 25°C virus was undetectable on days 12, 8, 5, and 4 days post infection (dpi), respectively. In C. v. sonorensis both the infection rate and rate of virogenesis were related to temperature. At 25°C a maximum mean titre of 104.3 TCID50/fly was reached by 9 dpi and the infection rate remained between 60 and 80%. At 20°C virogenesis was slower and a maximum mean titre of 104.3 TCID50/fly was reached only after 23 days; the infection rate was also reduced to 50–70%. At 15°C there was an overall decline in virus titre with time, although between 12 and 15 dpi some pools of flies contained 103.0–104.0 TCID50/fly, demonstrating that virogenesis can occur. The infection rate at this temperature decreased dramatically to 0–15% after 9 dpi. At 10°C there was no detectable virogenesis and all pools tested at 13 dpi were negative. The apparent infection rate dropped to 0–5% between 13 and 35 days post infection. However, when surviving flies were then returned to 25 °C for 3 days the infection rate increased to 15.5%. It therefore appears that at low temperatures the virus does not replicate but infectious virus may persist at a level below that detectable by the usual assay systems. The implications of these findings for the epidemiology of AHS are discussed.

Cacopsylla pyricola (Förster) is one of the most important pests of pear in North America, where several native predators have been considered for integrated pest management (IPM) programmes. Two molecular markers of 271 and 188 bp were developed from C. pyricola cytochrome oxidase I (COI) fragments, in order to study the detection of this species in the gut of arthropod predators. Primer sensitivity and the detection period for pear psylla remains in the guts of Anthocoris tomentosus Pericart were determined. The sensitivity threshold was defined at 10-5 dilution of a C. pyricola fifth-instar nymph in all samples. Predator adults were evaluated immediately after ingestion of one to five C. pyricola nymphs (t = 0) and after 2, 4, 6, 8, 16, 24 and 32 h. Detection of the presence of C. pyricola DNA always lasted longer using the shorter fragment and was observed after 32 h of digestion using both markers. The primers amplifying the 188 bp fragment amplified all four psyllid species tested, whereas the primers designed to amplify the 271 bp fragment did so exclusively for C. pyricola and its close relative, Cacopsylla pyri (Linnaeus). Both primers failed to amplify DNA from representative species of the Coccinellidae, Chrysopidae, Hemerobiidae, Anthocoridae, Miridae, Salticidae, Aphididae, Tetranychidae and the Tortricidae, suggesting their suitability for general trophic studies.

Following a long and varied history, Glossina control has become increasingly dependent upon the use of insecticides. There have been substantial successes with the use of chemicals, but reinvasion has been a constant, wide-spread problem. It is increasingly obvious that tsetse control must be approached on a large scale and requires international funding. Despite the proven ability of insecticides to reduce tsetse infestations there is a general reluctance to expand their usage and non-chemical methods are receiving increasing priority. In this paper, an attempt is made to put tsetse control into perspective. The literature relating to various insecticidal methods and tsetse control operations involving ground spraying, helicopter residual spraying, application of low dosage aerosols from fixed-wing aircraft and chemically impregnated traps is reviewed, and research and development relating to both the entomological and application aspects of chemical control are discussed. It is concluded that, given our present state of knowledge, insecticides provide the most reliable method for large-scale tsetse eradication. Of the methods available, applications of low dosage aerosols from fixed-wing aircraft have the greatest potential for rapid and effective control over large areas with minimal risk of non-target contamination, although refinements to improve efficiency and economy are needed. An integrated insecticidal approach combining the attributes of various chemical, and possibly non-chemical, control methods with the proven large-scale capability of spraying from fixed-wing aircraft could provide a realistic answer to the persistent Glossina and trypanosomiasis problems.

The success of distinguishing blood meal sources of Anopheles gambiae Giles through deoxyribonucleic acid (DNA) profiling was investigated by polymerase chain reaction (PCR) amplification at the TC-11 and VWA human short tandem repeats (STR) loci. Blood meal size and locus had no significant effect on the success of amplifying human DNA from blood meals digested for 0, 8, 16, 24 and 32 h (P = 0.85 and 0.26 respectively). However, logistic regression found a significant negative relationship between time since ingestion and the success probability of obtaining positive PCR products among meals digested for between 8 and 32 h (P = 0.001). Approximately 80% of fresh blood meals were successfully profiled. After 8 h, the proportion of blood meals that could be successfully profiled decreased slowly with time after ingestion, dropping to below 50% after approximately 15 h. There was no significant difference in the success of amplifying human DNA from blood meals of mosquitoes killed at time 0 and 8 h after ingestion (P = 0.272).

DDT-resistant Anopheles gambiae Giles from Zanzibar, Tanzania, had increased levels of DDT-dehydrochlorination compared to a DDT-susceptible strain. Glutathione S-transferases (GSTs) are responsible for conversion of DDT to DDE in both the susceptible and resistant strains. Sequential column chromatography, including Q-Sepharose, S-hexylglutathione agarose, hydroxylapatite and phenyl Sepharose, allowed the partial purification of seven GSTs. All seven GSTs possessed different degrees of DDTase activity. There was an eight-fold increase in total DDTase activity in the resistant compared to the susceptible enzymes. Characterization with three substrates, 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB) and DDT, revealed the different substrate specificity for each isolated GST indicating different isoenzymes. GST Va possessed 60% of total DDTase activity suggesting that it contributed most to DDT-metabolism in this insect species. The DDTase activity of the GSTs in both strains of A. gambiae were found to be correlated with the GST activities toward DCNB. Preliminary studies on DDT-resistant and susceptible A. gambiae showed that both DDT-resistance and the increased levels of GST activity were stage specific which suggested that different GSTs may be involved in DDT-resistance in adults and larvae of A. gambiae.

Almost all of the studies here reported were made in one small region, so that very little new information was secured on the ranges of the species of mosquitos under consideration.

Our investigations regarding breeding-places were limited to a few species. Aëdes vittatus was found occasionally breeding in tree-holes in Ibadan. Aëdes irritans adults were taken at Ibadan, which is so far inland that this species must sometimes breed in places other than crab-holes at the edges of salt or brackish water. We did not, however, find the larvae of this species at Ibadan. The favourite breeding-place of Eretmopodites chrysogaster was found to be small collections of water in fallen leaves (especially those of cocoa trees) lying in moist and densely shaded places. Because of the abundance of Mansonia africana in places practically free from Pistia, we conclude that in the vicinity of Lagos it must breed abundantly on other plants. The long flight range of this species was taken into consideration in arriving at this conclusion. An extensive search failed, however, to reveal these plants. M. uniformis, also abundant in the vicinity of Lagos, does not breed there upon Pistia, but an extensive search failed to reveal its breeding-place.

The brackish water form of A. gambiae on the East African coast—and probably in Mauritius—is not the same as A. melas of West Africa.

In salt-water gambiae a variable proportion of the females have an additional dark band on the palps, resembling 4-banded melas, but the remainder are indistinguishable from typical gambiae.

Eggs and larvae of salt-water gambiae show no morphological differences from those of fresh-water gambiae, thereby differing from A. melas of West Africa.

Larvae of the two forms show a clear-cut difference in reaction to sudden changes in salinity, and a simple test has been worked out whereby wild-caught females can be accurately identified by the reactions of their progeny.

This physiological test has formed the basis of all work in comparing the incidence, habits, and infectivity of salt and fresh-water gambiae in Dar-es-Salaam.

Exposed to equal chances of infection in the same village during 1947 and 1948, fresh-water gambiae had a sporozoite rate of 9·4 per cent. while that of salt-water gambiae was 0·8 per cent.

About 4 per cent, of both forms were infected with filaria larvae, but monthly figures showed that infection rates in salt-water gambiae may rise to 22 per cent.

Fresh-water gambiae show little tendency to leave African houses at dawn after feeding, whereas in salt-water gambiae over one-third of freshly blood-fed females leave the house at dawn.

In fresh-water gambiae many half-gravid females leave the shelter of the house at dusk on the night after the blood feed. There is no marked difference in infectivity between those which leave the hut and those which remain indoors at this stage.

Blood-fed and gravid females of fresh-water gambiae, funestus, and salt-water gambiae have been found in outdoor resting places, gravid females predominating in the case of the first two.

Although larvae of salt-water gambiae can complete their development in pure sea water, in nature increasing salinity becomes a limiting factor before it reaches that of sea water, continuous breeding being no longer possible at salinities over 83 per cent. sea water.

Salinity as a limiting factor explains the rather restricted breeding of salt-water gambiae on the coast, and suggests that certain coastal fresh-water swamps at Dar-es-Salaam could be cleared of all Anopheline breeding by salinifying with sea water.

Sites in the humid forest of Cameroon and the derived savanna of Benin were selected to evaluate the effect of planting border rows of wild host plants on lepidopterous stem-borer infestations and on maize yield. Grass species were chosen that in surveys and greenhouse trials were highly attractive to ovipositing female moths but with offspring mortality of close to 100%, thus acting as trap plants. In Cameroon, elephant grass Pennisetum purpureum Moench significantly lowered infestations of Busseola fusca (Fuller), Sesamia calamistis Hampson and Eldana saccharina Walker and increased yields of maize though the differences were not significant during all three cropping seasons. In 1998 in Benin, the only grass tested, Pennisetum polystachion L., significantly increased parasitism of mainly S. calamistis eggs by Telenomus spp. and larvae by Cotesia sesamiae Cameron and reduced numbers of the cob-borer Mussidia nigrivenella Ragonot. In 1999, three grass species; P. polystachion, Sorghum arundinaceum (Desv.) Stapf and Panicum maximum Jacq. were tested. Panicum maximum was the most efficient species for suppressing S. calamistis and M. nigrivenella infestations and enhancing egg and larval parasitism. In the Benin trials, with the exception of M. nigrivenella damage to cobs, the grass species tested had no beneficial effect on yield because pest densities were too low and also rodent damage to maize was enhanced with grasses in the vicinity of the crop. By contrast, stand losses due to Fusarium verticillioides Sacc. (Nirenberg), were significantly reduced by border rows of grasses.

Five capture-recapture experiments with three species of the group of Anopheles punctulatus Dönitz were undertaken in four villages in Madang Province, Papua New Guinea. Females were collected in landing catches, blood-fed, marked with fluorescent powder according to time and location of capture, and released. Recaptures took place for 4–13 nights after release. A proportion of the recaptured mosquitoes was dissected for evidence of recent oviposition and gonotrophic age determination. Two models were developed to test a number of the assumptions that underlie the analysis of capture-recapture data from mosquitoes. Species abundance and numbers collected varied within and between villages, but marked mosquitoes dispersed at random within the mosquito population. No heterogeneity was found between indoor and outdoor biters of any of the three species. Survival rates were similar in all species. Significant differences were found in the duration of the oviposition cycle between species and village. This was 2·7–3·7 days for A. punctulatus, 2·4–3·2 days for A. koliensis Owen and 2·1–3·0 days for A. farauti Laveran. No differences were found in the duration of the oviposition cycle of nulliparous and parous females of A. farauti. Thus temporary pool breeders had a longer cycle than permanent pool breeders. This tended to be due to a delay in returning to feed rather than a delay in oviposition. It is concluded that differences between local environments exert a greater influence on the duration of the oviposition cycle than do species specific differences.

Locomotor activity in an actograph and oriented locomotor movements in an olfactometer were recorded for fifth-instar nymphs of Rhodnius prolixus Stål exposed to test stimuli expected to elicit food-seeking behaviour. A natural food source (hamster or human forearm) proved to be the most attractive stimulus. Warmth alone was least stimulating for long-range orientation. As with mosquitoes, carbondioxide and moisture proved to be attractive, as well as the odour of a hamster. Lactic acid did not seem to play an important role in orientation. Activation by the different stimuli was most pronounced during the scotophase of the circadian cycle. Circadian activity ran-free for two weeks in constant darkness. The results indicate that the stimuli that elicit locomotor activity in the actograph are in some way implicated in the switching of the taxis mechanisms that utilise the airstream for orientation.