Maize is the major food crop in Kenya, where 2.3 million tonnes are produced annually to feed an estimated 28.6 million people (79 kg/person p.a.). Population growth in the country is high (2.9 % p.a.), resulting in increased pressure on arable land and, consequently, increased pest pressure on crops. Stemborers are one of the most important pests of maize. Previous research with artificial infestation established clear links between damage factors and yield losses. These results, however, cannot be extrapolated to estimate crop losses in farmers' fields under natural infestation. Due to lack of field data, farmers' (often subjective) estimates of losses under natural infestation and the incidence of infestation were used to estimate maize yield losses for each of Kenya's major agroecological zones. The yield loss was estimated to be 12.9 %, amounting to 0.39 million tonnes of maize, with an estimated value of US$ 76 million. High-potential areas have relatively low crop loss levels (10–12 %), while the low-potential areas have higher losses (15–21 %). Taking into account the higher yield of the former areas (more than 2.5 t/ha), the loss per hectare is remarkably constant, between 315 and 374 kg/ha, except for the dry mid-altitude zones, where losses total approximately 175 kg/ha. The value of these losses is estimated at US$ 61–75/ha and US$ 34/ha, respectively. Such estimates are useful for setting research and extension priorities.

—Infochemicals play an important role in the biology of many insect species. An understanding of their role in plant-herbivore-carnivore interactions can be used in the development of tools for the enhancement of environmentally benign alternatives to synthetic pesticides. This review discusses how chemical information mediates ecological interactions between organisms and the role of infochemicals in integrated pest management. Infochemicals can be used in pest monitoring and in pest control, through mating disruption, mass trapping and to aggregate herbivores at delivery sites for biological control agents. Particular emphasis is placed on the potential of using pheromones and kairomones in the management of the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), a pest in plantations of East African highland banana and plantain in most banana-growing regions of the world. Cosmopolites sordidus produces an aggregation pheromone that attracts both males and females. This pheromone has been identified and synthesised and is being recommended as an effective agent in the trapping and control of the weevil. The synergism between banana plant extracts (kairomones) and the synthetic pheromone in attracting C. sordidus should be better exploited. Future research areas that can provide information for the development of an infochemical-based trapping system for the management of C. sordidus are discussed.

A strain of diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), adapted to peas was detected in 1999 in the export vegetable growing area south of Lake Naivasha in the Rift Valley Province of Kenya. The pea strain (DBM-P) was compared in laboratory studies to the normal crucifer strain (DBM-C). Whereas DBM-P performed comparably well on kales and peas, the cabbage strain (DBM-C) suffered heavy mortality on peas. Out of the 250 DBM-C first instars, only six reached adult stage on pea. In addition, larval development was prolonged by five days on peas as compared to kale, and larval growth was greatly reduced. Pupal weights of DBM-C survivors on pea were significantly lower (3.8 mg) than of DBM-P (4.6 mg) and those of both strains on kale (5.7 and 5.3 mg, respectively). Neonate larvae of the pea strain mined on both kale and pea but both the proportion of larvae mining and the number of mining days were lower than for DBM-C on kale. The latter failed completely to mine on pea.

A laboratory culture was started with the DBM-C survivors on pea and the performance of the progeny compared on kale and pea in three additional generations of selection. Larval survival increased from 2.4% in the first generation to 28.6%, 41.3% and 49.7% in the second, third and fourth generation, respectively. Pupal weight of larvae reared on pea increased with each generation of selection, but it remained significantly lower than of larvae reared on kale. In spite of the large differences in larval mining on the two host plants, performance on peas was not related to the ability of DBM-C to mine on pea but rather to the ability to initiate feeding without the normal stimuli present in crucifers. Pupal mortality for larvae from both hosts was similar when larvae of equal weight were compared, suggesting acceptable suitability of pea for larval development once the new host is accepted. The implications of these findings on adaptability of DBM to plants beyond its normal host range are discussed.

—Native to the Caribbean islands and Central America, the spiralling whitefly, Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae), has spread to North America, South America, Asia, Africa, Australia and several Pacific islands. A total of 62 natural enemies, including 8 parasitoids, 53 predators and one fungal pathogen, are known to attack the whitefly in different countries. Of the parasitoids, the accidentally or deliberately introduced aphelinids Encarsia sp., Encarsia (?) haitiensis Dozier and E. guadeloupae Viggiani provide control of A. dispersus in many countries. The exotic coccinellid predator Nephaspis oculata Wingo also plays an important role in reducing the whitefly's populations. However, the A. dispersus remains a pest in some countries in the absence of parasitoids. This article reviews current information on biological control of A. dispersus in different countries/states, in particular India, the Pacific islands, Hawaii and countries in West Africa.

The demographic statistics of the ladybird Exochomus flaviventris Mader (Coleoptera: Coccinellidae) were investigated under laboratory conditions on the cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae), reared on four host plants with different levels of antibiotic resistance to the mealybug: two cassava (Manihot esculenta Crantz, Euphorbiaceae) varieties, Incoza and Zanaga, Faux-Caoutchouc (FC) (hybrid of M. esculenta × M. glaziovii Muel. Arg.) and water weed (Talinum triangulare Jack, Portulacacae). Preimaginal mortality, mean oviposition time and total fecundity of female ladybirds were strongly affected by the host plant even though there was no linkage with antibiotic resistance. The net reproduction rates R0 of the predator were 1.5,1.7 and 2.4 times higher on Zanaga than on water weed, Incoza and FC respectively, and the generation time (T) was significantly longer on Zanaga than on the other three plants. The intrinsic rate of increase rm was not modified by the antibiotic resistance of the host plants. With the two cassava varieties, Incoza and Zanaga, it was found that antibiosis significantly affected the life history parameters of the ladybird without modifying its fitness, and provided better cassava mealybug control.

Several Vigna species were used to determine the role of pod trichomes and pod toughness in the resistance of cowpea to feeding damage by the coreid bug Clavigralla tomentosicollis Stal. The scanning electron microscopy study revealed the presence of glandular and non-glandular trichomes on the pod wall of all test genotypes. The cultivated genotypes TVu 1890, TVu 3354 and IT84S-2246 of the V. unguiculata ssp. unguiculata showed significantly lower (P<0.05) densities of glandular trichomes than accessions of the wild Vigna species (TVnu 72, TVnu 151, and TVnu 707). All pods were similar with respect to the density and length of non-glandular trichomes. The two wild accessions TVnu 151 and TVnu 707 of the V. unguiculata ssp. dekindtiana had low pod, strength similar to that of the susceptible genotype IT84S-2246, and also showed high seed damage levels comparable to that of this susceptible genotype. These accessions of the subspecies dekindtiana contrasted with the wild and resistant accession TVnu 72 of the V. vexillata species which suffered minor seed damage in spite of its low pod strength. The association between high pod strength and low seed damage was found only in the two cultivated genotypes TVu 1890 and TVu 3354. Our results suggest that tough pod wall and high density of glandular trichomes can be combined to achieve enhanced resistance to C. tomentosicollis in cultivated Vigna genotypes.

It is known that in citrus orchards, the citrus psyllid Trioza erytreae (Homoptera: Triozidae) preferentially chooses certain varieties for egg laying, feeding and larval development. However, the selection mechanism in citrus nurseries is poorly understood. The aim of the present work was to study in the nursery, the behaviour of T. erytreae with respect to choice of egg laying and feeding sites in three species of citrus, namely Villafranca lemon, Mexican lime and Fremont mandarin. One hundred young plants of each were exposed to the citrus psyllid on the fourth month after germination, and psyllids and pit galls counted every month. The impact of the psyllid's damage on citrus was also assessed. Adults of T. erytreae were highly attracted to the young citrus plants three weeks after the germination of seeds. The average number of adults, eggs and larvae of T. erytreae by plant varied with the particular citrus plant: on young plants, adult, larval and egg populations were highest on lime. Four months later, 100 % of lime, 97% of lemon and 76 % of mandarin plants were attacked by T. erytreae. Those plants attacked shortly after germination were stunted and their leaves greatly deformed. In the absence of pest management in the citrus nursery, citrus psylla can cause the loss of up to 91 % of young plants.

From August 1988 to January 1997, natural enemies were reared from 335 colonies of Plnnococcus citri Risso (Homoptera: Pseudococcidae) sampled for 87 months from 225 randomly selected cocoa farms in the six cocoa-growing regions in Ghana. A total of 20,408 P. citri individuals was recorded, comprising adult females, third instar nymphs and mummified individuals harbouring parasitoids. Observed predators were larvae of Coccodiplosis coffeae Barnes (Diptera: Cecidomyiidae), nymphs and adults of Hyperaspis egregia Mader and Scymnus (Pullus) sp. (Coleoptera: Coccinellidae), as well as an unidentified lepidopteran. Twelve parasitic Hymenoptera were also reared, including Aenasius abengouroui (Risbec), Leptomastix dactylopii Howard, Anagyrus beneficions Compere, Tropidophryne melvillei Compere, Anagyrus amoenus Compere and Chryptochetum (Lestophonus) spp. Also recorded were a hyperparasitoid, Cheiloneurus carinatus Compere, parasitising Coc. coffeae, Xyplugaster pseudococci Risbec and six rare, undetermined parasitoids. Coccodiplosis coffeae was the commonest parasitoid, occurring throughout the year and infesting 72.8% of the P. citri colonies. Parasitism levels were generally low, the highest mean being 4.6 ± 2.6% for Aen. abengouroui. Simultaneous parasitism by more than one species was common and this gave rise to mean monthly parasitism levels ranging from 0.8 to 4.5%. Aenasius abengouroui, Ana. amoenus and H. egregia are being reported for the first time in P. citri on cocoa in Ghana, and the recovery of L. dactylopii suggests its establishment in the country, where it was introduced in 1949.

Thirty-five grain sorghum genotypes representing 6 variable groups (A/B-lines, R-lines, commercial varieties, germplasms, mutants and locals) were evaluated for the orientation, colonisation and oviposition responses of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), governing the antixenosis component of resistance. In free-choice tests, the orientation and colonisation responses of the weevil were identical among all the genotypes at 24 h, varied at 48 h, and differed widely by 72 h after adult release. High degrees of antixenosis for colonisation by the adult weevils were observed among all the genotypes except 2077A and 2219B, which suggests a predominant reaction to gustatory rather than visual or olfactory stimuli. One to five egg plugs per seed were oviposited, frequently near the endosperm close to the seed base. Greater levels of antixenosis for oviposition were noticed in 2077B, DJ 6514 and IS 11758 in free-choice tests, and 2219B, M 148–138, P 721 and Nizamabad (M) in no-choice tests. To the contrary, M 35–1, Swati and Lakadi showed greater susceptibility for oviposition. Significantly less damage to seed was observed on 2219A/B, 116B, IS 9487, IS 11758, CSV 8R(M) and Local Yellow. Although the differences in seed weight loss were not significant, this parameter was relatively lower in AKMS 14B and 2219B than in the other genotypes. This indicates the need to increase the levels of resistance among the parental A/B-lines in the development of hybrids, in order to ensure better protection from rice weevil infestation in stored sorghum.

The effect of infestation of lepidopteran borers on yield of maize was assessed at three locations in the forest and forest/savanna transition zones of Cameroon, during the first and second season of 1992. Maize was treated once or twice with the systemic carbofuran at different developmental stages. The species encountered were the stem-boring noctuids Busseola fusca and Sesamia calamistis, which oviposit on and attack pre-tasseling stages of maize; the stem-boring pyralid Eldana saccharina, which attacks plants at and after tasseling; and two ear borers, namely the pyralid Mussidia nigrivenella and the tortricid Cryptophlebia leucotreta. Generally, carbofuran reduced infestations by B. fusca and S. calamistis but had little or no effect on species attacking the plant's later stages. Thus early treatments with granules into the whorl were more efficient than late treatments as a side dressing, and a second late treatment had little effect. During the first season, late-attacking species were predominant and grain yield losses of 17–44 % were found in one location only. During the second season, species attacking young plants (mainly B. fusca) became predominant in all three locations and yield losses of 30 to 41 % were found in two of the three locations. The percentage of ears with damage was especially high during the second season. As green maize is an important source of cash income in the area and damaged ears cannot be sold, the economic loss was likely considerable.

—The community structure and diel activity patterns of peridomestic Stomoxyinae at two locations in Nairobi and its outskirts (Chiromo and Ruiru) were studied using Nzi traps baited with octenol. Six species of Stomoxys (S. calcitrans, S. niger niger, S. n. bilineatus, S. inomatus, S. taeniatus, S. varipes) and three other Stomoxyinae genera (Haematobosca, Stygeromyia, Parastomoxys) were caught. At Chiromo, species diversity (H') varied from 0.29 to 0.65 and evenness from 0.59 to 0.83, whereas at Ruiru, diversity varied from 0.0 to 0.38 and evenness from 0.0 to 0.46. Diurnal activity both S. calcitrans and S. n. niger was bimodal, with a small peak of activity in the morning (0800–1100 hrs) and a major peak in the evening (1700–1800 hrs). Both species showed a midday depression in activity. The activity of S. inomatus rose steadily throughout the day with only a slight midday depression. These results are discussed with respect to results of similar studies in a natural, undisturbed habitat.

The termite species Macrotermes bellicosus has a vast geographical distribution, which can produce genetic divergence in populations that evolve in its different environments. Experiments carried out on digestive oxidases in two populations of M. bellicosus originating from Chad and from Côte d'lvoire showed differences in the rate of their enzymatic activities. Populations from Côte d'lvoire showed significantly higher degradation activity against fresh vegetal matter than populations from Chad.

—The efficacy of triflumuron was tested on three types of textiles (cotton, polyester and polypropylene) of two colours (blue and black) for application in self-sterilisation of Glossina palpalis gambiensis Vanderplank, 1949 (Diptera: Glossinidae). Three concentrations of triflumuron diluted with water to 3, 6 and 12 % were used to impregnate each type of cloth and two groups of tsetse flies were contaminated—females aged 20 days were directly contaminated by exposure to impregnated cloth; and younger females (3-days-old) were contaminated during the mating by males treated like old females. The blue and black-coloured cloths had no significant differences in terms of reproductive parameters (P<0.05). On the other hand the type of fabric and the concentration of triflumuron had significant effects on the efficacy of the product. Cotton and polypropylene, impregnated with triflumuron diluted to 6 and 12% respectively sterilised the old females on 5 consecutive reproductive cycles from normal pupa production. The two concentrations also sterilised the younger females on 3 consecutive reproductive cycles from pupal hatching. Polyester impregnated with the same concentrations sterilised the old females during the 3 first reproductive cycles after treatment and young females on 2 reproductive cycles.

Studies were conducted to determine the effect of temperature and diet on the development of Chilo partellus (Swinhoe) and Chilo orichalcociliellus (Strand) (Lepidoptera: Crambidae). Developmental times of C. partellus and C. orichalcociliellus for the egg, larval and egg-adult life stages were inversely related to temperature. The larval developmental period of C. orichalcociliellus reared on artificial diet was longer than the developmental period on natural diet. Chilo partellus had a higher intrinsic rate of natural increase than C. orichalcociliellus at all diet/temperature combinations except natural diet at 31°C.

The age-dependent fecundity and offspring production of females of a solitary ectoparasitoid Dinarmus basalis Rond. (Hymenoptera: Pteromalidae) were determined on its host Callosobruchus maculatus F. (Coleoptera: Bruchidae). The resulting data were used to determine the longevity and reproductive potential of the species, by establishing its life and fertility tables. In the presence of 16 hosts renewed every 48 hours, D. basalis females had a mean longevity of 32.6 ± 1.6 days. They laid an average of 136.5 ± 55.2 eggs, parasitised 132.7 ± 53.9 hosts, and produced 111.8 ± 3 offspring, consisting of 58.3 % of males and 41.7 for females. The total mean development time was 14.0 ± 0.7 days for females and 11.8 ± 0.8 days for males. The net reproductive rate (Ro) was 38.9 females progeny per adult female, and the intrinsic rate of population increase (rm) 0 16 per day. The generation time (G) was 22.5 days and the doubling time (DT) 4.3 days. These parameters permitted to determine the reproductive potential of D. basalis as a biological control agent against the bruchid in West Africa.

—The sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of gut supernate antigen (GS Ag) derived from partly fed Hyalomma anatolicum anatolicum Koch, 1844 (Acari: Ixodidae) adult females revealed 26 discrete potypeptide bands of molecular weight ranging from 25–208 kDa. Out of these, seven bandswere of major polypeptides with molecular weights of between 25.2 and 185.8 kDa. On immunoblotting with antisera raised in rabbits against gut supernate (crude extract), eight immunogenic polypeptides with molecular weights of between 51.7 and 185.8 were identified. The implications of these findings for the potential development of anti-tick vaccine are discussed.

Surveys for population densities of the maize borer Sesamia eretica Led. (Lepidoptera: Noctuidae) were conducted for three consecutive years (1997–1999) in several localities of the Nile delta in Egypt, in order to get a better insight into the population dynamics of the pest and to propose rational basis for its biocontrol using a recently isolated granulovirus. High population densities (more than one borer per plant) were observed only in the first plantings after winter (first fortnight of April). After this peak, populations almost vanished until the end of the crop season (September-October) when a slight increase was observed (0.1 borer per plant). The drastic decrease in population densities in plantings from the end of April occurs because most final instars of the borer leave the plant to pupate in the soil. This behaviour, uncommon in maize borers, results in a very high mortality rate due mainly to pupal parasitism. Only the few larvae pupating in the stem, which are much less parasitised, give rise to adults. Spatial distribution was studied using Taylor's power laws which enabled the elaboration of enumerative sampling plans for eggs, small larvae (1st and 2nd instars) and older ones. Fixed optimal sample size and sequential sampling plans for different precision levels were developed. The precision of the estimated sample size was checked using resampling of some of the data that were not used to build the models. The validation study showed that the plans were suitable for the entire Nile delta region.

Field experiments were conducted to investigate the attractiveness of fish bones to predatory ants in a maize agroecosystem. The fish bones were applied crushed in shallow furrows together with dry maize stalks, or broadcast on the soil surface at 3 application rates: 0, 40 and 80 kg/ha; subsequent reduction in termite attack on maize plants was then assessed. Burying the fish bone powder caused higher ant nesting (10–78 %) than surface broadcasting (12–39 %). Attractiveness of the fish bones and the predatory efficiency of the ants against termites in maize was also highest with a dose of 80 kg/ha (1.0 kg/plot) causing higher nesting of ants (>90 %) and 54 % lower termite damage to maize plants compared to control plots. Dose responses indicated significant relationships between amount of fish bone powder applied and termite activity and also between termite damage and maize yield. The mechanism by which the ants are able to protect maize against termite damage may be twofold: direct kill as a result of their predatory action and termite avoidance of maize plants with ant nests. Further studies are required to assess the potential benefits of an integrated use of this technique with other non-chemical options for termite control in maize, such as intercropping.

The recent development of geographic information systems (GIS) provides new avenues for analysing spatial patterns in insect populations. Field survey data, along with GIS and statistical models were used to predict the distribution of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) in Ethiopia. The results obtained suggested that the distributions of Ch. partelhis and Co. flavipes were affected by rainfall and temperature. The predicted distributions of Ch. partellus and Co. flavipes were similar. Validation of predicted values is discussed.