A field survey on maize stemborers, stemborer damage, maize plant physical conditions, and maize yield was conducted in eastern Kenya under natural conditions. Chilo partellus was the dominant stemborer accounting for 89.5 % of all borers. Stemborer damage greatly reduced maize yield, with tunnel lengths greater than 20 cm causing a 40 % reduction of potential yield. A 33 % yield loss was found in plants with more than one stemborer exit hole. Each stemborer (at harvest time) was correlated with a 8–10 % yield loss. Good plant physical characteristics significantly increased grain yield. Principle component analysis showed that stemborer damage, plant height and stem diameter were key factors affecting maize grain yield. Regression analysis indicated that one centimetre of stemborer tunnel reduced yield by 3 g/plant. Multiple regression analysis implied a 13.3 ± 1.5 g yield loss (8–10 % of potential yield) due to the damage of a single stemborer. Comparison with average yields in the study area suggested that our results were representative of losses on farmers' fields.

Laboratory experiments using a glass tube arena were conducted to determine the effects of aggressive behaviour of the stemborer, Chilo partellus Swinhoe (Lepidoptera: Pyralidae), on oviposition success and mortality of the parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae). On contacting unparasitised hosts, female parasitoids rapidly oviposited and then retreated from the experimental arena. Hosts exhibited no aggressive behaviour prior to oviposition. However, soon after being attacked, host larvae became more aggressive, spitting at and biting the parasitoids. When Co. flavipes females were introduced toward the head of the stemborer, the parasitoids stung the host near the head and were frequently bitten and killed by the hosts. Parasitoids that were introduced to the host from the posterior end of the abdomen, stung the abdomen and were often able to escape from the host without being bitten. Regardless of whether parasitoids were introduced near the head or the abdomen, they were more often killed by older hosts than younger hosts. Parasitised hosts were more aggressive than unparasitised hosts one hour after the initial parasitisation, but not after 24 hours. Larval saliva of Chilo partellus was found to reduce survival of adult female parasitoids. The aggressive behaviour of Ch. partellus was not effective as a self-defense against Co. flavipes, but is likely to be an important mortality factor of Co. flavipes in nature.

The tomato red spider mite Tetranychus evansi Baker & Pritchard is a serious pest of solanaceous plants worldwide. Management of this oligophagous pest in African nightshades has been a challenge to smallholder African farmers due to its high reproductive rate and rapid development of resistance to synthetic pesticides. The aim of the present study was to determine the influence of leaf trichomes on T. evansi by comparing its fecundity and movement on the leaf surfaces of five African nightshade species, namely Solanum sarrachoides Sendter, S. villosum Miller, S. tarderemotum Bitter, S. americanum Miller and S. scabrum Miller. Data were recorded in the laboratory at 23 ± 1°C, 50–70% relative humidity and a 12 h light:12 h dark photoperiod for the effect of trichome type and density of the abaxial leaf surface on mite fecundity. Distances travelled by mites on the leaf surface from the edge of a thumbtack pin inserted on the leaf were also recorded. Different trichomes, glandular and non-glandular types, were identified. There was a significant negative correlation of fecundity and distance walked by mites with the density of glandular trichomes. Significantly fewer eggs were laid on S. sarrachoides in comparison with the other Solanum species. The distance walked by mites was also significantly shorter in this species, indicating that higher densities of glandular trichomes interfere with mite movements. These results suggest that African nightshade genotypes differ in their levels of resistance to T. evansi, which is partially associated with differences in trichome types and their densities.

Satureja hortensis and Zataria multiflora (Lamiaceae) essential oils were tested on Callosobruchus maculatus (Fabricius) to evaluate their effects on oviposition deterrence, egg hatching and mortality of adults. To obtain essential oils, dry leaves were subjected to hydrodistillation using a modified Clevenger-type apparatus. The experiments were conducted at 25 ± 1°C and 65 ± 5% relative humidity in dark conditions with five replications for each essential oil. When concentrations of both essential oils were higher, the insecticidal effect on eggs and adults increased and oviposition was more deterred. At the highest concentration (60 μl/l air) of S. hortensis and Z. multiflora essential oils, 91.2 and 85.4% of adults were killed, respectively. There were no significant differences in oviposition deterrence between the two essential oils. At the highest concentration (4.3 μl/l air) of S. hortensis and Z. multiflora essential oils, egg mortality was 94.5 and 77.3%, respectively. Probit analysis revealed LC50 for adults and eggs of C. maculatus of 1.50 and 1.13 μl/l air, respectively, for the S. hortensis essential oil and 1.76 and 2.23 μl/l air, respectively, for the Z. multiflora essential oil. The results suggest that the essential oils of these aromatic plants can be used as botanical fumigants to protect grains against C. maculatus.

An automatic insect release system (AIRS) has been developed by the International Institute of Tropical Agriculture in collaboration with Firma Dieringer of Austria and Ciba-Pilatus (now Zimex Aviation) of Switzerland for the aerial distribution of natural enemies of two cassava pests—cassava mealybug (Phenacoccus manihoti) and cassava green mite (Mononychellus tanajoa). The AIRS, installed in a twin turbo-prop aircraft, has undergone a series of tests to evaluate suitable packaging substrates, pre- and post-release mortality, biological performance and ground distribution of natural enemies.

Preliminary results show 25% of the mealybug parasitoid, Epidinocarsis lopezi died from packaging to release, maximum 25% died during the release and minimum 50% survived. The mortality of predatory mites released in small packages was negligible. Further work on post-release survival and dispersal is needed.

Thrips, Frankliniella occidentalis (Pergande), is a major invasive pest that causes extensive yield losses in French bean and tomato in Kenya. Thrips management is based on the application of pesticides. In addition to increased environmental risks associated with pesticides, frequent use of these chemicals increases production costs and pesticide resistance. Furthermore, exports are restricted due to non-compliance to maximum residue levels in important consumer export markets, especially the European Union (EU). This study was conducted to estimate the potential benefits of the effectiveness of the icipe-developed strategy for control of western flower thrips before dissemination of the technology in Kenya, using the economic surplus model. We calculated the benefit–cost ratio, the Net Present Value (NPV) and the Internal Rate of Return (IRR) using Cost–Benefit Analysis (CBA). Assuming a maximum conservative adoption rate of 1% and a 10% discount rate for the base deterministic scenario, the NPV of the research was estimated at US$2.2 million, with an IRR of 23% and a BCR of 2.46. Sensitivity analyses indicated that the NPV, IRR and BCR increased at an increasing rate as adoption rates increased. However, as elasticities of supply and demand increased, the NPV, IRR and BCR increased at a decreasing rate. The findings demonstrate that farmers from developing countries can gain when they obtain access to suitable pest management innovations such as integrated pest management technologies. Consequently, investment in IPM technologies for suppression of western flower thrips should be enhanced.

Petroleum ether extract of Eichhornia crassipes (Mart) Solm. was evaluated for its biological activity against Tribolium castaneum (Herbst), Sitophilus oryzae (L.), Callosobruchus maculatiti (F.) and Corcyra cephalonica (Stainton). The crude extract included in the diet of insects retarded development and caused mortality in the fourth instar larvae of T. castaneum and C. cephalonica. Cuticle melanization in patches were observable in C. cephalonica larvae. High mortality of adult C. maculatus occurred in insects confined to the treated diet as well as in insects exposed to treated surfaces. The extract did not show any toxicity to adult S. oryzae.

Aleurolobus barodensis (Maskell) was more abundant than Neomaskellia andropogonis Corbett on sugar-cane in Pakistan. Azotus delhiensis Lal, Eretmocerus sp., Prospaltella flava Shafee, Amitus sp. and Tetrastichus sp. parasitized nymphs and pupae of A. barodensis and E. serius Silvestri those of N. andropogonis. Chrysopa carnea Steph., Brumoides suturalis (F.), Catana parcesetosa (Sic.), Oenopia sauzeti Muls., Scymnus sp. and S. nubilus Muls. preyed on the immatures of the aleurodids.

In Peshawar valley where the crop is aerially sprayed twice a year to control Chilo infuscatellus Sn., Tryporyza nivella F., A. barodensis and Pyrilla spp., the rate of parasitism on A. barodensis was very low and its density was very high, being 330 immatures/leaf at Charsadda and 425 at Mardan in November 1979. At Sialkot (Punjab) where the crop is not sprayed, the rate of parasitism, mainly by A. delhiensis and Amitus sp., at this time was 22% and the density of A. barodensis was 70.4 immatures/leaf. The maximum rate of parasitism was 71% in January. The abundance of A. barodensis in Peshawar valley seems to be due to the mortality of natural enemies because of aerial spraying, therefore, judicious use of insecticides and redistribution of natural enemies in these areas is recommended.

Life-fertility tables were described for Bracon hebetor Say (Hymenoptera: Braconidae) developing on the millet head caterpillar (MUC), Heliocheilus albipunclella de Joannis (Lepidoptera: Noctuidae). Mated B. hebetor females lived an average of 24.7 days, oviposited ca. 22 days, and produced 173.7 adult progeny with a 1:1 sex ratio. The estimated innate capacity of increase (ir) and net reproductive rate (R0) were 0.26 and 86.5, respectively. The mean generation time was 1 days.

Isolates of Beauveria bassiana (Balsamo) Vuillemin, Paecilomyces farinosus (Holm ex SF Gray) Brown and Smith and Verticillium lecanii (Zimmermann) Viegas were evaluated for their pathogenicity to adults, eggs, first and third instars of silverleaf whitefly, Bemisia argentifolli (Bellows and Perring) (Homoptera: Aleyrodidae). Conidial dilutions were prepared in 0.05% Tween® and leaves treated by immersion in these suspensions. Assessments of nymphal infection were made 2, 3, 5, 7, and 10 days post-treatment. Infection rates in adults and eggs were made 14 days post-treatment. All isolates were pathogenic to nymphs and adults. None of the isolates were pathogenic to eggs. Isolates L3444 (P. farinosus) and L3009 (B. bassiana) were the most pathogenic to first instars and adults with LC50 and LC90 values of 7.3 × 104 and 3.1 × 106 conidia/ml, and 1.3 × 106 and 1.0 × 107 conidia/ml, respectively. Isolate FR20 (V. lecanii) was the most pathogenic to third instars with LC50 and LC90 values of 4.8 × 103 and 7.4 × 105 conidia/ml, respectively. Results imply that L3444 and L3009 are the most efficient isolates, based on their pathogenicity to first instars and adults. Results are discussed in relation to using fungi for management of silverleaf whitefly in greenhouses.

Methanolic extracts of stems and roots of silver fern, Cheilanthes farinosa Kaulf., (Polypodiaceae: Pteridophyta) incorporated into a semi-synthetic diet significantly extended the larval period, reduced pupal weight and adversely affected pupation of the cotton bollworm, Helicoverpa armigera (Hübner) (Noctuidae: Lepidoptera). Early third instars were more susceptible to the treatment than late third instars. A steroidal fraction (Rf 0.7) from the methanolic extract significantly reduced mean larval weight but did not affect pupation. A major ecdysteroidal component (R.t. 9.233 min.) was purified by reverse phase HPLC of this fraction, along with two minor components. The total yield of ecdysteroids was 564 mg/kg of shade-dried root and stem matter. Pooled HPLC fractions, when injected into final instars, resulted in dose-dependent effects on larval-pupal transformation. Adults emerging from treated larvae failed to lay eggs and were shorter-lived than their untreated counterparts.

The insecticidal activity of essential oils extracted by steam distillation from six aromatic plants from Togo, Cymbopogon schoenanthus (L.) Spreng., C. citratus (D.C.) Stapf., C. nardus (L.) Rendle, Lippia multiflora Moldemke, Eucalyptus citriodora Hook., Diplolofium africanum Turcz., was tested against the cowpea weevil, Callosobruchus maculatus F. Concentrations of 6.7; 10.0; 16.7 and 33.3 μ1/1 were evaluated. The chemical composition of the essential oils used was established by GC/MS analysis. Only C. schoenanthus oil showed significant insecticidal activity at 6.7 μl/1 oil (LC50 2.3 μ1/1). At concentrations higher than 33.3 μ1/1, all test plants showed similar insecticidal activity; more than 90% of the test insects died within 24 hours of exposure. Oviposition was also reduced significantly by the essential oil treatments.

The biology of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), on four legumes (faba bean, field pea, lentil and grass pea) was studied in a greenhouse during the 1999/2000 seasons. There was no significant difference in length of nymphal period and number of moults (instars) among the crop species tested. The aphids generally took 9 to 11 days to reach the adult stage with a maximum of 3 moults. Lifespan was significantly longer on lentils than on other crops. Significantly more aphids survived beyond 15 days on lentil than on other crops. Similarly, the reproductive and post-reproductive period and adult longevity were longer on lentil. The pre-reproductive period was significantly higher on field pea than on the other crops. The net reproductive rate (R0) was highest on lentil (103.56 females /female) arid the intrinsic rate of increase (r) was highest on faba bean due to a short generation time (14.27 days). Generally, lifetime fecundity was higher on lentil (115.10/female) due to a higher daily reproduction rate (6.7 nymphs/female/day) on this crop. Nymphal production per aphid was strongly and positively correlated with lifespan, reproductive period and adult longevity but not of the nymphal period. Daily nymph production was significantly correlated with minimum temperature on lentil alone (F = 4.61, P < 0.05). Knowledge of the crop species and varieties susceptible to pea aphid is useful for identifying diets for the mass rearing of aphids for use in resistant variety selection and as diet for artificial natural enemy production. The present experiment indicates that lentil is suitable for both purposes.

From the literature review and available information on Chilo in the seven Oceanian countries, only six species of Chilo have been recorded as pests of graminaceous crops. C. terrenellus Pag. is one of major sugar-cane pests, in Papua New Guinea and a minor sugar-cane pest on Saibai, Torres Strait Islands, Australia, respectively. In the former country, the damage assessment, host plants, life cycle, phenology and natural enemies of the stem borer have been studied. Since 1981, two larval parasites, Apanteles flavipes Cam. (Indian strain) and Bracon chinensis (Szep.), have been introduced against the stem borer from India, propagated and released but have failed to become established. The search for additional parasites continues. C. influscatellus Sn. is a minor sugar-cane pest also in Papua New Guinea; C. suppressalis (Walk.), C. polychrysa (Meyr.), C. auricilia Dudg. and Chilo sp. are minor pests of rice in Papua New Guinea; the former two species are also minor rice pests in the Northern Territory, Australia where integration of cultural, chemical and biological control measures have been applied against the major white rice borer, Scirpophaga innotata (Walk.), in conjunction with C. suppressalis and C. polychrysa.

A review of the losses caused by various species of Chilo, methodologies adopted for the assessment of losses and information generated on the models for the effect of Chilo species on the yield of graminaceous crops is given.

The effect of an alkaloidal fraction from the stem bark of Artabotrys odoratissimus R. Br. on larvae of the mosquito vector of lymphatic filariasis, Culex quinquefasciatus Say, was investigated. Concentrations of 10, 20, 40, 80, 160 and 320 ppm were tested in the laboratory against larvae of various ages. A general increase in lethal concentration 50 (LC50) values from the second to fourth instars was observed. Based on overlapping confidence intervals (CIs), the LC50 value following 12 h of exposure was lowest for the second instar (59.2 ppm) and was significantly different from that recorded for the fourth instar (110.4 ppm). LC50 values decreased significantly with time (from 12 to 24 h after treatment) in all the instars. These results indicate the potential utility of the A. odoratissimus extract as a mosquito larvicidal agent, and further research is recommended.

Antixenosis resistance to Helicoverpa armigera (Lepidoptera: Noctuidae) was studied in 10 tomato accessions selected from a germplasm of 321 at Tamil Nadu, India, using free-choice and no-choice laboratory experiments. The foliage and fruits of two accessions, namely PT 4287 and Varushanadu Local were the least preferred for feeding in both tests. In the no-choice (confinement) test, Seijima Jeisei, Varushanadu Local and PT 4287 were the most preferred for oviposition, but had low egg hatch rates. In the free-choice test, these accessions were the least preferred for oviposition. The first and second instars preferred to feed on the foliage of 30- and 45-day-old plants, respectively than 60- and 75-day-old plants, whereas ovipositional preference was insignificant among the various plant ages.

Lepidopteran stemborers, mainly the African stemborer Busseola fusca Fuller and spotted stemborer Chilopartellus Swinhoe, are among the economically important pests of sorghum in Kenya. Identification of sources of resistance is valuable for the development of an integrated pest management strategy to minimize losses. This study evaluated 27 genotypes with artificial infestations (mostly for tolerance) in two different agroecological zones. Data on damage from leaf feeding, dead heart, exit holes, and stem tunnelling; plant height; days to 50% flowering; total grain yield; and hundred-grain mass were collected. Significant differences (P< 0.001) were observed in all the traits evaluated, except leaf damage, under infestation by C. partellus. Classification into different categories of resistance revealed genetic variation. Genotypes resistant/moderately resistant to both pests were as follows: ICSA 464>ICSB 464>ICSB 467>ICSA 472>ICSB 472>ICSA 473>ICSA 474>IESV 91131 DL>Macia. The relative contributions of the damage parameters to grain yield loss were partitioned into direct and indirect relationships by path coefficient analysis with grain yield as the resultant variable. The results revealed that damage from exit holes, dead heart, leaf feeding and stem tunnelling had a negative indirect effect on grain yield. The identified genotypes can be used to enhance resistance to both pests in susceptible cultivars that farmers prefer.

Several insect pests are associated with the sorghum crop, but essentially a few are considered key pests. These include shootfly, several species of stem borers, sorghum midge and a complex of head bugs. Other insect pests which are occasionally devastating and sporadic include leaf feeders and defoliators (Lepidoptera of various genera, locusts, grasshoppers, aphids, beetles, etc.) and also several species of head worms and head beetles. A list of 101 insect pests of sorghum occurring in Africa is presented.

Laboratory studies were carried out to determine factors which induce larval diapause in a Nigerian strain of Plodia interpunctella.

Larvae reared at constant temperatures of 20 or 30°C did not enter diapause. However, 13.3 and 37.7% respectively of larvae reared for 8 or 12 days (third or fourth instars) at 30°C and then transferred to 20°C entered diapause. Larvae transferred to 20°C immediately after hatch (first instar) and after 16 days (final instar) did not enter diapause. Developmental periods from egg-hatch to adult of diapausing individuals ranged from 136 to 151 days, while those of non-diapausing individuals reared at constant temperatures of 30 and 20°C ranged from 23 to 34 days and 60 to 72 days, respectively.

Different photoperiods did not induce diapause when reared at constant temperatures but exposure of larvae that experienced a drop in temperature from 30 to 20°C, at 4th instar stage to continuous light or to a long photoperiod (light 16 hr: dark 8 hr) caused a drop in the percentage larvae that diapaused.

Larvae reared at high larval density at 30°C did not enter diapause, and increased mortality was observed.