Two field-collected strains of Culex quinquefasciatus Say, collected 50 km apart in Havana City, Cuba, were both resistant to malathion and propoxur, while one population also showed low level resistance to temephos. Laboratory selection of the latter population with malathion for 22 generations increased the malathion resistance 1050-fold, temephos resistance 24-fold and propoxur resistance 453-fold compared to the standard laboratory susceptible strain. Synergist studies and biochemical tests indicated that two mechanisms, an elevated esterase and an insensitive acetylcholinesterase, were operative in these strains. The esterase mechanism conferred resistance to malathion, but not to temephos or propoxur. The acetylcholinesterase mechanism increased the level of malathion resistance and extended the cross-resistance spectrum to temephos and propoxur.

Mean survival times for unfed ticks, Rhipicephalus appendiculatus Neumann exposed initially during the hot dry season (January) in Kenya were significantly higher than those of ticks exposed during the wet season (May). This was partly due to the timing of the next hot dry season which triggered the beginning of decline in survival, and partly due to the overall severity of the weather. The implication is that the time when the ticks feed affects the survival of the subsequent instar. The mean survival times for nymphs exposed initially during the wet and the hot dry seasons were 30 weeks and 44 weeks, respectively. Those for adult ticks ranged between 59–75 weeks and 62–79 weeks, respectively. Maximum survival times were, however, similar for adults but not for nymphs. Adult ticks had an initial period of 32–48 weeks of excellent survival, apparently independent of weather factors. Thereafter, mortality rates and adverse environmental factors were correlated. The survival of ticks fed on hosts of differing resistance status was also different. The most resistant host produced the smallest adult ticks and these gave the lowest survival, and vice versa. Male and female ticks from highly resistant hosts had similar survival, but the females from a moderately resistant host survived significantly better than the males. These results indicate the importance of weather and host resistance in R. appendiculatus survival.

The effectiveness of pitfall traps baited with cattle dung enclosed in a gauze bag and pads of cattle dung on soil as methods for sampling dung beetle populations was assessed in the summer-rainfall regions of South Africa using 17 species of nocturnal/crepuscular tunnelling beetles. Pitfall traps accumulated the catch and prevented both access to and emigration from the dung bait. In contrast, beetles had direct access to dung pads on soil which allowed colonists to modify the bait and to emigrate. The number of beetles collected was therefore the net result of immigration and emigration. On each of five occasions in November–December 1985, 40 pitfall traps and 40 dung pads were set out in the evening and the trapped beetles recovered the following morning. Overall, 3774 individuals were trapped. For most species there was no significant difference between trap types in the numbers caught but two species were significantly more numerous in pitfall traps and one species was more numerous in the dung pads. However, both methods produced similar patterns of rank abundance of species (r=0.95). There was no evidence that beetles were more evenly distributed between dung pad baits than between pitfall traps.

A field trial was carried out in a Maasai group ranch to assess the use of odour-baited traps for suppression of a population of the tsetse fly Glossina pallidipes Austen. In January, 1987, local people made 100 NG2B traps in their homesteads. These were then deployed within the suppression zone of about 100 km2, primarily in the areas of woodland where flies aggregate in the dry season. Traps were baited with acetone (ca. 150 mg/h) and cow urine (ca. 1000 mg/h) and checked at monthly intervals in order to replenish odours and repair damage. A further 90 traps were added between October and December to enlarge the suppression area slightly and to strengthen the trap barriers. The population was monitored using biconical and NG2B traps as well as by mark-release-recapture estimates of population size. By October the number of G. pallidipes in the suppression zone was reduced by 98–99% relative to the number 3 km outside the suppression zone. Some reinvasion, mainly of parous females, occurred in November during the short rains but these flies were rapidly trapped out again. Average mortality rates due to trapping were estimated at 4–5% per day, which, combined with the natural mortality, reduced the adult population at a rate of about 2.6% per day during the dry season. The traps had less effect on the smaller population of G. longipennis Corti but still gave a reduction of up to 90% in the dry season. The use of this low technology approach offers good prospects for future community-based tsetse control operations.

Hodotermes mossambicus (Hagen) is a harvester termite which competes with livestock for natural grazing. Control by baiting is recommended. Field trials in the north-western Orange Free State and south-western Transvaal, Republic of South Africa, showed that the two most commonly used commercial baits, with carbaryl or sodium fluosilicate as the active ingredient, are ineffective in controlling this species. A simple mathematical model was developed to rate the acceptability of grasses as food for the termite colonies. This enabled the attractiveness of the bait carriers as food for termites to be compared with that of the grasses. All five grass species tested had a similar food acceptability value, while both bait carriers were unacceptable as food. Failure of the baits was due to the fact that they were not consumed by the termites. The active ingredients was found to be effective when natural grass was used as the bait carrier. The mathematical model was extended to elucidate the effect of different baits on colony survival. This approach could be further used to rate new baits and their carriers objectively.

A method for intensive screening of cowpea for resistance to Maruca testulalis (Geyer) is described. It is capable of ensuring uniform infestation and thus eliminating problems due to escapes. Four cowpea varieties earlier identified from field screening trials as resistant (TVU 946, TVU 1896 AG, H 51–1 and 2 AK) and three susceptible varieties (Ife Brown, H 144–1 and 58–185) were screened using this method. The results confirmed the status of the resistant varieties. Some effects on M. testulalis included, non preference for oviposition and larval feeding, and antibiosis manifested by reduced final larval instar weight, elongated pupal period and smaller sized emerging adult females.

Factors involved in the origin of plagues of Schistocerca cancellata (Serville) in Argentina were examined using a simple model for locust development. Plagues were present in 48 of the 58 years between 1897–1954 with plague sequences occurring before 1900, 1903–11, 1913–28, 1931–38 and 1944–54. Plagues originated when winter rain fell in the outbreak areas in La Rioja and Catamarca resulting in three generations in a season. Plagues continued for 8–15 years. Their decline was usually gradual resulting from a combination of several seasons when it was dry in the outbreak areas, and only one generation per year was possible. Before 1954, locust swarms were common in 15 of Argentina's 22 provinces but it was not obvious where the plagues originated. Since then most swarms have been reported from two provinces in the northwest: La Rioja and Catamarca. Within these provinces, bands and swarms have been most common in the semi-arid outbreak area. Populations have been highest when the outbreak area received winter/spring/summer rain which allowed three generations in a season. However, infestations have never approached plague proportions in recent years because regular control of bands and swarms in the outbreak area has kept populations in check.

The influence of the lepidopteran stem borer Scirpophaga incertulas (Walker), the most important pest of deepwater rice (Oryza sativa) in south-east Asia, on plant and grain yield was investigated in Bangladesh during 1982–85. Four mechanisms of crop loss were identified: (i) deadhearts at the vegetative stage, (ii) loss of damaged but apparently healthy stems in flood water, (iii) white-heads at the reproductive stage and (iv) the effect of late season stem damage on panicles. A great proportion of damaged stems was not visible and damage symptoms were found to be an unreliable indicator for the assessment of borer activities in the field, and did not represent the actual yield loss. Stem damage had a negative influence on the stem density, with reduced panicle density and grain yield. Stem borer damage also seemed to reduce the elongation ability of the rice stem causing them to rot. Late season stem damage reduced the number of filled grains, mean grain weight and panicle weight and increased grain sterility. These effects were related to severity and position of damage. The average estimated yield loss due to S. incertulas was about 17% which took place during the last 11 weeks (from flood peak to crop maturity) of the deepwater rice season (32 weeks).

Non-chemical control of termites in agriculture and forestry is attracting renewed interest following increasing restrictions on the use of persistent organochlorine (cyclodiene) insecticides. Non-chemical control involves methods which attempt, without using commercial pesticides, to (i) prevent termite access to the plants, (ii) reduce termite numbers in the vicinity of the plants or (iii) reduce susceptibility/increase resistance of the plants themselves. There have been few adequate trials of any of these methods. Numerous cultural procedures have been suggested, including measures to enhance plant vigour, to manipulate termite numbers and behaviour, and others whose mode of action is unclear. Many are simply part of good agricultural/silvicultural practice and to be recommended. Biological control by predators or pathogens is unlikely to be successful due to the termites' social structure and behavioural responses to infected individuals and to loss of individuals to predators. The use of ‘natural’ insecticides from locally available plant products may be effective in some cases but, as they are not subject to the same rigorous safety and environmental evaluation as commercial pesticides, their use cannot be sanctioned unconditionally. Other locally available products, e.g. wood ash, have not been adequately evaluated. Removal of reproductives from the nest and construction of physical barriers may have limited applications, but resistant species and varieties, combined with appropriate cultural methods and, perhaps, minimal use of modern pesticides in an integrated approach, offer the greatest potential for a long term solution. The lack of critical scientific evaluation of non-chemical control makes it a field wide open for research.

Gene flow between field populations of the cereal aphids Sitobion avenae (Fabricius), Sitobion fragariae (Walker) and Rhopalosiphum padi (Linnaeus) is examined using statistical analyses of allozyme frequency data (both Slatkin's and F statistics). Analysis using Slatkin's method confirms the conclusions previously drawn from earlier analyses. Thus there is found to be high gene flow between subpopulations of S. avenae and R. padi, and a more restricted level between local S. fragariae subpopulations, especially when infesting the secondary host (cocksfoot grass, Dactylis glomerata). The value of Nm (number of immigrants per generation) calculated for S. avenae was approximately 2 and is indicative of high gene flow i.e. Nm>1.0. Also, as previously found by x2 genetic contingency testing, the F statistical analysis confirms that S. fragariae subpopulations infesting D. glomerata are genetically more heterogeneous than those infesting the primary host, blackberry, Rubus fruticosus agg. Hence, there may be less gene flow between populations on the secondary host compared with that on the primary. The results obtained are compared with the flight behaviour of these particular aphid species and to their respective host plant abundances. The advantages and disadvantages of both Slatkin's method and F statistics for analysing insect population genetic structure are noted.

Phlebotomus perfiliewi perfiliewi Parrott and Phlebotomus perniciosus Newstead (Diptera: Psychodidae,) known vectors of Leishmania infantum were caught in light traps in five different sites in Italy. Sandflies were cryopreserved and transported to the laboratory where they were thawed and aqueous extracts of the crushed flies were analysed for their carbohydrate content using high performance liquid chromatography. Several sugars were detected, including significant amounts of the trisaccharide melezitose, known to be available as a natural source from aphid or coccid honeydew. There was no difference between the analyses of sugar meals of P. p. perfiliewi from different sites within its range, or between P. p. perfiliewi and P. perniciosus. The results indicate that both males and females of P. p. perfiliewi and P. perniciosus feed on honeydew.

Antibiosis of resistant melon lines to the carmine spider mite, Tetranychus cinnabarinus (Boisduval), was evaluated in the laboratory. Significant differences among lines were observed seven days after the inoculation of detached leaf disks. The most resistant lines, namely CHI-8, BUS-7 and BUS-3, reduced the average mite daily fecundity by 49%, 40% and 33%, respectively, as compared to the susceptible NY line. Resistance did not appear to be related to the growth habit. Selfing resistant melon parents resulted in a significant increase in the number of plants on which female mites produced less than one egg per day.

Extracts of different sesame plant (Sesamum indicum) Linnaeus organs inhibited the in vitro growth of the fungus Leucocoprinus gongylophorus (Möller) (=Rozites gongylophora Möller), which is cultivated by the leaf-cutting ants of the species Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). The presence of the factor responsible for this inhibition was detected in methanol or chloroform extracts and is constant in the plant.

The effect of a range of temperatures (15–42°C) and relative humidities (40–80%) on growth of populations of Liposcelis entomophilus (Enderlein), Liposcelis bostrychophilus Badonnel and Liposcelis paetus Pearman infesting a rice-based medium was investigated. These species are often found infesting stored cereal grains in the tropics. Both L. entomophilus and L. bostrychophilus bred most rapidly at 30°C, 70–80% r.h. Neither survived at temperatures of 36°C and above. In contrast, L. paetus bred most rapidly at 33–36°C, 70% r.h., and was able to breed at 42°C, 80% r.h. No species survived humidities below 60%. As well as consuming mould growth, Liposcelis spp. also caused visible damage in rice grains. Implications of these findings in the understanding of pest status and geographical distribution of severe outbreaks of Liposcelis spp. are discussed.