Four designs of trap, all made from identical material, were compared at Galana Ranch, south-eastern Kenya, as sampling devices for Glossina pallidipes Austen and G. longipennis Corti. The NG2G and Epsilon traps caught more than twice as many female G. pallidipes as the biconical trap, and the F3 was intermediate. A similar, pattern was observed for males, although the differences were smaller, and not significant. The NG2G, Epsilon and F3 traps all caught approximately twice as many male and female G. longipennis as the biconical trap. Acetone (500 mg/h) significantly increased trap catches of G. pallidipes, and there was a synergism between acetone and 4-methylphenol (0.8 mg/h). There was little or no effect with 1-octen-3-ol (0.8 mg/h). Acetone, 1-octen-3-ol, and 4-methylphenol all increased trap catches of G. longipennis, and there were no synergisms among them. Cow urine (850 mg/h) increased the catches of both species in traps baited with acetone and 1-octen-3-ol, although not significantly for G. longipennis. There was no effect with 3-methylphenol (0.8 mg/h). The addition of 3-propylphenol to traps baited with acetone, 1-octen-3-ol and 4-methylphenol had no effect on the catches of either species. For G.pallidipes, a combination of acetone, 1-octen-3-ol, 4-methylphenol and 3-propylphenol was calculated to have a catch index of 6–8 over unbaited traps, a value lower than that reported for Zimbabwe and Nguruman, Kenya, and greater than that reported for Somalia. The catches of G. longipennis were approximately three times higher on electrified targets than in F3 traps, although there was no difference in the catch of G. pallidipes.

The behaviour and pest status of the rice stem borers Diopsis longicornis Macquart and D. apicalis Dalman were investigated in the Republic of Guinée, particularly during the dry season. The variables were direct seeded and transplanted rice, and three (1988, 1989) and four (1987) planting dates. Transplanted rice was damaged nearly three times more than direct seeded rice in the dry season, but no significant difference was detected during the wet season. As previously observed in other West African countries, D.apicalis only occasionally damages rice in Guinée. Contrary to findings elsewhere, D. longicornis was not an important pest of Guinean rice, infesting only 5% and 3% of stems over the three dry and the two wet seasons, respectively. However, year round rice production could promote build up of the diopsid population if dry season planting is not sufficiently delayed (45 days) after the last rains of the wet season.

A plot of cocoa trees at the Cocoa Research Institute, Tafo, Ghana, was inspected weekly for the presence on each tree of 18 species of insects. The 306 consecutive weekly records of percentage of trees occupied by each species were subjected to time series analysis. Auto-correlation and partial auto-correlation functions were calculated for each series and used to identify simple autoregressive linear models to account for the serial correlation. It was found that all species needed a stabilizing autoregressive parameter of lag 1 and all but four a second autoregressive parameter of lag 2. Seasonal autoregressive parameters at lags 3, 4, 5, 7, 9, or 13 were needed for over half the species, either in addition to the parameter at lag 2 or in place of it. It is postulated that these seasonal parameters mimic generation cycles. Runs of the models using random inputs produced series which were close to the originals in general form. The models could be further refined by adjusting the fixed mean levels assumed by the models to take into account the effects due to the abundance of young extension growth on the trees and atmospheric moisture, as measured by afternoon relative humidity readings. Although the production of extension growth is cyclical it would seem that it does not induce the cyclical behaviour observed in some of the insect series. The peaks in the latter cycles are, however, reinforced when they coincide with peaks in extension growth.

Predatory arthropods on cabbage terraces were studied by square flooding and by pitfall trapping in January 1992, following a transect through the Cordillera Region of Luzon, with decreasing numbers of insecticidal sprays per year. Predator numbers were sampled along this transect per 4 m2 and with 15 pitfall traps per site. The dry biomass of predators was also measured. The four sites studied were classified as two pairs, one with high input of insecticides and low predator numbers, low biomass and diversity, the other with low insecticidal input and high predator numbers, high biomass and diversity. The number of ant (Hymenoptera: Formicidae) genera per 15 pitfall traps increased along the transect, showing that ants might be used as indicators of the insecticidal intensity for growing vegetables in the Luzon Cordillera Region. Compared with Europe, the potential abundance and diversity of predators in the Philippines proved to be very high. The reasons for the large differences between sites concerning abundance and diversity of predators are discussed, together with conclusions drawn from the findings presented.

Over a period of six years, the presence or absence of 23 species of arboreal insects (13 Homoptera, 1 Heteroptera, 9 ants (Hymenoptera: Formicidae)) was recorded on each of 866 young Amazon and Amazon hybrid cocoa trees at the Cocoa Research Institute, Tafo, Ghana. The general form of the time-series, derived from the proportion of trees occupied by each species, is described. Analysis of 18 of these series, taken either singly or jointly, was carried out using analysis of variance and principal components analysis and the degree of spatial association between 16 of the species was also investigated. For the latter, the number of joint occurrences of pairs of species was compared with the expected number by means of a chi squared test. An index of association was derived from the proportion of occasions on which the difference was significant. For all but four species, there were highly significant differences between annual means in the analysis of variance and, in many, the overall annual trend was downward with time. For those species where significant differences were not shown between years, trends were often apparent on individual plots but were negated because of inconsistencies between plots in the direction of the trend. In the joint analysis of all 18 species by principal components, the first component accounted for approximately 33% of the total variance and could be identified as representing to a large extent the long-term upward or downward trends shown up by the analysis of variance. The second principal component, accounting for a further 13% of total variance, was interpreted as being a further manifestation of the long-term trend, representing a tendency for deviation from the trend line shown up by the first component to become less with time and to approach the trend line in a damped oscillation. This is thought to be partly caused by a drought at the start of the experiment which affected certain species adversely. The third principal component accounted for 11% of total variance and the scores followed an irregular annual cycle which was related to relative humidity. The scores on this axis were high during dry periods of the year and low during wet periods. In the analysis of variance it was found that 13 species showed significant differences in spatial distribution between seasons and, for most, there was evidence for an annual cycle. There was also some evidence of correlation between the seasonal cycles of some insects with seasonal rainfall level or morning or afternoon relative humidity. These same species are important in contributing to the third principal component scores. Spatial association analysis showed eight species to be strongly associated. These fell into three groups with positive associations between members of the same group and negative association between members of other groups. Each group featured an ant-homopteran association, Crematogaster spp. with Planococcoides njalensis (Laing) in group 1, Oecophylla longinoda (Latreille) with Stictococcus spp. in group 2, and Camponotus spp. and Polyrhachis laboriosa F. Smith with Planococcus citri (Risso) and Toxoptera aurantii Boyer de Fonscolombe in group 3. Three other coccids were loosely linked to these groups through particular members, Waxiella sp. nr zonatus (Newstead) to group 1 through Planococcoides njalensis and to group 2 through Camponotus spp. and Phenacoccus hargreavesi (Laing) and Steatococcus spp. to group 2 through Planococcus citri. Changes taking place with time in the relative abundance of members of these groups could be discerned in the trajectories of the first two principal components. The spatial re-arrangements taking place with time of the territories of the major ant species are followed in some detail, and the effect of these changes on Homoptera is discussed.

In surveys of cassava fields in the coastal savanna and rain forest zones of Ghana, eight species of ants, mostly in the genera Camponotus, Crematogaster and Pheidole (Hymenoptera: Formicidae), were found attending cassava mealybug, Phenacoccus manihoti Matile-Ferrero. Ant densities were much higher in the rain forest than in the savanna and, in most zones, positively correlated to mealybug population densities. Pheidole megacephala (Fabricius) was the only species more abundant in the interior of fields, whereas the other species preferred the edges of fields or, like Camponotus spp., did not respond to edge effects. Weediness of the fields did not clearly influence the presence of ants. Crematogaster sp. and P. megacephala spent most of the time on cassava tips, where they built carton tents. Ants of the three genera reduced parasitism rates by the exotic Epidinocarsis lopezi (De Santis) (Hymenoptera: Encyrtidae) to half, compared to the rates observed on mealybug colonies of equal size that were not attended. Hyperparasitism by Prochiloneurus insolitus (Alam) (Hymenoptera: Encyrtidae) and Chartocerus hyalipennis Hayat (Hymenoptera: Signiphoridae) and predation by the indigenous Exochomus troberti Mulsant (Coleoptera: Coccinellidae) were similarly reduced. Where ants were excluded experimentally by insectcide barriers, parasitism was 32%, compared to only 10% in the control, and predator densities were reduced three-fold. In a 24 h experiment, Pheidole megacephala was observed to remove about half the E. troberti larvae; Crematogaster sp. and Camponotus spp. were less efficient. The results show the locally strong interference of ants with biological control of the cassava mealybug. Despite this interference, mealybug populations in the rain forest were judged to be below damaging levels.

The Simulium sanctipauli Vajime & Dunbar subcomplex of the West African S. damnosum Theobald complex is cytotaxonomically revised for the western part of the Onchocerciasis Control Programme area. The subcomplex is defined and a chromosomal key provided for the identification of the sibling species and forms recognized. Two sibling species are newly described, S. leonense Boakye, Post & Mosha (Sierra Leone) and S. konkourense Boakye, Post, Mosha & Quilleévéré (Guinea and Sierra Leone). Detailed chromosomal data are provided as warranty for the conclusions about the specific or infraspecific status of the taxa recognized.

Smallholder crops (sunflower, maize, sorghum and cotton) were grown in experimental plots at seven sites, representing different agricultural zones of Kenya, over four seasons. Helicoverpa armigera (Hübner) (formerly Heliothis armigera) only occasionally achieved population densities sufficient to cause obvious damage to the crops, and was virtually absent from the coastal sites. At the inland sites, infestation and mortality levels varied greatly. Information is presented on the incidence of H. armigera, and the identity, distribution and frequency of its common parasitoids and (potential) predators, sampled in the experimental plots. Trichogrammatoidea spp., egg parasitoids, and Linnaemya longirostris (Macquart), a tachinid late-larval parasitoid, were the most common parasitoid species, but total percentage parasitism was rather low. Of the large complex of predators, only anthocorids and ants (predominantly Pheidole spp., Myrmicaria spp. and Camponotus spp.) were sufficiently common and widespread to be of importance in suppressing H. armigera. The abundance of predators fluctuated widely between sites, but anthocorids were most abundant at the western sites.

Gas liquid chromatography (GC) was used to analyse the cuticular alkanes of 26 species and subspecies of tsetse flies (Glossina spp.). Unique interspecific and intraspecific (males vs. females) chromatographic patterns were observed. Solvent extraction of dried museum specimens and fresh specimens were equally successful, and left specimens undamaged. GC peaks were used as characters with one of five character states per peak, to show phenetic relationships among species by sex using a UPGMA algorithm, using 23 peaks for males and 40 peaks for females. Comparisons among species of the morsitans group often agreed with recognized morsitans group classification using morphological techniques, with G. austeni Newstead being somewhat aberrant. Glossina tachinoides Westwood was less closely related to others in the palpalis group than previously described using morphology. Eleven members of the rarely studied fusca group were also classified by this methodology.

Video observations were made of tsetse flies (mainly Glossina pallidipes Austen) as they approached, responded to and left a vertical (1 m square) black target in odour plumes of acetone, or a 4:1:8 mixture of octenol:propylphenol: methylphenol, or acetone plus this “4:1:8” mixture, or in no odour. No differences in mean flight speed or turn size in any of these situations were detected. With the odour source 5 m upwind of the target, the flight tracks of tsetse arriving at and leaving the target were significantly biased towards upwind, highly so when 4:1:8 was present, marginally so in acetone alone. With the source 10 m upwind, the same biases were still present but weaker. Circling flights around the black target were more frequent in acetone plus 4:1:8 than in no odour (26% vs 15%), but in either odour alone were only just significantly more than in no odour. Upwind turning at the target was more frequent (25% vs 17%) in acetone alone that in no odour (though not in 4:1:8 alone). It is concluded that 4:1:8 elicits an upwind anemotactic response comparable in strength to that in CO2, and that acetone elicits a similar response more weakly, but may be more involved in potentiating visual responses.

Pyrethroid resistance was examined in adult Helicoverpa armigera (Hübner) in both laboratory and field selected strains. A series of F1 and backcrosses was made between a susceptible and an isofemale resistant strain. Dose-responses were obtained using contact with a treated surface inside a scintillation vial. Inheritance of resistance was consistent with an incompletely dominant major gene and resistance factors were greater than 100-fold. Piperonyl butoxide synergized the effects of the synthetic pyrethroid, fenvalerate, 1000-fold and eliminated resistance entirely. Field trials examined the mortality of resistant and susceptible adults exposed to commercial application rates of synthetic pyrethroids. Adults were immobilized and placed in cotton fields prior to aerial applications of insecticide. Survival of resistant adults was significantly greater than susceptible ones in both trials. It was concluded that selective mortality in the adult life-stage contributes to the evolution of pyrethroid resistance.

A strain of Musca domestica Linnaeus with low pyrethroid resistance was divided into four sub-strains, each was subjected to three selections in the laboratory with either alphacypermethrin, cypermethrin, deltamethrin or permethrin. Each selected strain was then tested for cross-resistance to the other pyrethroids and to synergized pyrethrins. Pyrethroid resistance was increased by all selecting agents by a factor of between 1.5 and 3.6 as measured at the KD50, thus demonstrating that the newer persistent pyrethroids had a similar potential to select for pyrethroid resistance as did permethrin. A field trial using a commercial alphacypermethrin formulation was carried out in an intensive animal unit against a population of M. domestica with a high pyrethroid resistance. After a high initial kill, the population rapidly recovered and a second application failed to control the population. Pre- and post-trial M. domestica samples were taken and resistance to alphacypermethrin and synergized pyrethrins was shown to have increased from 54.5 to 263.6 and 15.2 to 28.4 at the KD50, respectively.

Field sampling of populations of Sitobion avenae (Fabricius) on spring wheat in the north-western USA from 1988 to 1991 produced a data set consisting of 47 estimates of mean aphid density (m; number of aphids per tiller), variance (s2) and the proportion of tillers (PT) with no more than T = 0, 1, 2, …10, 15, 20, and 25 aphids, respectively; defined as the tally threshold. The average sampling error level of the four-year data set was 0.196 (SE= 0.013). The empirical relationship between m and PT was developed for each T value using the parameters from the linear regression of ln(m) on ln[-ln(Pϒ)] and was satisfactory when T = 2, 3, 4, and 5 (as evidenced by the high r2 values and relatively small mean squared errors from the regression analyses relating to the T values). In comparing the variances estimated from different formulae for predicting m from PT, the variance of Binns & Bostanian (1990b) was found to be more conservative and reliable in estimating the prediction variance. This variance was used in the development of binomial sampling plans for each T and in the determination of associated sampling precision denoted by the half-width of the confidence interval (d). Binomial sample sizes based on the T values of 2–5 were found to be associated with relatively small d values that may actually be reached and thus, are recommended for use in monitoring aphid populations for control decision making. However, at population densities below one aphid per tiller, binomial sampling was found to be feasible only when counts were based on empty tillers (T = 0).

Trissolcus crypticus sp. n., a sibling species of T. basalis (Wollaston), is described. Introduced from Pakistan into Australia and Hawaii (via Australia) as a ‘strain’ of T. basalis, it was widely released for the biological control of Nezera viridula (Linnaeus). In Australia, the species reputedly gave widespread control of N. viridula populations in inland and northern areas. Examination of all available T. basalis specimens in Australia failed to discover any T. crypticus (other than voucher specimens) and its role as a biological agent warrants reassessment.

Male Glossina morsitans morsitans Westwood and Glossina pallidipes Austen caught in artificial refuges in Zimbabwe had ca. six times as much haematin and up to 32% more fat than flies from odour-baited traps, but haematin-specific fat levels did not differ significantly between methods. G. pallidipes estimated to have fed < 9 h prior to sampling contained ca. 3.3 mg fat - only 10% less than peak levels. A differential equation model for blood-meal metabolism was developed which described well the changes in fat levels of laboratory G. m. morsitans and the relationship between fat and log haematin in field data. The model predicts a mean feeding interval (T) of 54 – 65 h and mean fat levels of ca. 2.8 mg for G. pallidipes at feeding. When haematin frequency data were analysed as suggested in the literature, estimates of feeding rates and intervals, and of the non-feeding phase, varied with sampling method. Published estimates of activity levels related to feeding suggest a model where feeding rates increase approximately linearly during the trophic cycle. For T = 58 h the model gives good predictions of mean fat levels and variances in both species, with starvation rates < 1% / day. Models with long non-feeding phases predict fat levels up to 40% lower than observed and with smaller variances. For constant feeding rates, fat levels were well predicted for T = 54 h, but predicted death rates (> 5% / day due to starvation alone) were impossibly high. It is suggested that a proportion of tsetse flies with high fat levels feed on mobile hosts early in the trophic cycle and that this effect is more marked for G. m. morsitans than for G. pallidipes. Over-estimates of T result from the failure to consider these tsetse flies and not to errors in the assumed time scale, nor failure to catch high-fat tsetse flies which visit stationary traps.

The probablity that tsetse flies (Glossina spp.) cross a barrier of odour-baited targets is calculated for barriers of different widths and target density, and for tsetse flies with varying natural rates of survival, daily step lengths (d) and probabilities of being killed by an odour-baited target. If the barrier is only as wide as d, and for a species which has a 2% natural daily mortality and a further 2% mortality due to each target per unit area, tsetse flies have probability (P) of ca. 0.1 of penetrating the barrier even if the target density is 64 per unit area. To ensure that P < 0.001 the barrier must be about 4d wide for target densities 32 per unit area; doubling the width to 8d means that target densities could be cut by about 75%, and total numbers of targets in the barrier by 50%. These biological considerations and the economic costs of different target barriers suggest that, for all tsetse fly species, a safe and relatively inexpensive barrier is achieved with barrier width 8d when the optimum target density is roughly the same as for normal operational areas. This has the important practical consequence that there is no need to treat barriers as a special case. Practical results from research and control operations in Zimbabwe are in accord with the theoretical findings, but further work is required to ascertain whether the safety margin, and hence costs, can be reduced.

Comparisons of infestation and damage levels by the cotton bollworms, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), Earias vittella (Fabricius) and E. insulana (Boisduval) (Lepidoptera: Noctuidae) were made in cotton fields treated with pheromones + insecticide, insecticides only, and untreated control plots, in Pakistan during the 1991 cotton season. Early to mid season control of these three pests by mating disruption in the pheromone + insecticide treated plots meant that an average reduction of 3.5 applications of insecticides was achieved when compared with the insecticide only treated plots to control the cotton pest complex. Night observations showed that there were far fewer adult moths visible in the pheromone + insecticide treated plots than in insecticide only treated plots. Adults of both sexes were much less active and did not mate as frequently as adults in the insecticide only plots.