The leaf miner Coelaenomenodera lameensis Berti and Mariau (Coleoptera: Chrysomeiidae, Hispinae) is the main oil palm pest in Africa. A study of variations in its fecundity, in space and time, was carried out at 7 plantations and 19 sites in Côte d'lvoire. Fluctuations in fecundity, which could vary from almost 300 eggs to just a few eggs per 90-day period, were very similar at the various sites of the same plantation, and at the sites of different plantations, even when these were very far apart from each other. Fecundity increased with temperature, but other climatic factors were also important, with air saturation deficit playing a decisive role. The drier the air, the lower was the fecundity, which could even reach almost zero. As this parameter had a considerable impact on palm leaves' stomatal opening, a highly significant correlation was established between the latter and fecundity. Food supplies for larvae and adults can also affect fecundity, which seems to vary with the potassium content of the leaves.

Studies on the population dynamics and species composition of the sorghum stemborers Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Sesamia sp. were conducted at Melkassa, Rift Valley of Ethiopia, during the 1990 and 1992 cropping seasons. Chilo partellus at 92% dominated the species composition. Busseola frisca made up 7.7% and Sesamia calamistis less than 1% of the borers. Occurrence of partellus declined with delay in planting until the third planting ( early June to early July) then increased during late planting in July. Busseola fusca alone, however, tended to increase in numbers with delay in planting. In Melkassa area, early planting in July could be considered as the most suitable, with low borer numbers, damage symptoms and resulting in fewer stalks with peduncle damage. Grain yield was also higher during early planting in July while the lowest yield was obtained during late planting in July. Weather factors showed no consistency but relative humidity seemed to have a significantly negative correlation with insect numbers in the last two plantings in 1992.

The occurrence of an orange body coloured mutant, governed by a single somatic recessive gene of the cotton stainer, Dysdercus koenigii is reported. Both the strains did not show any quantitative difference in growth, development and reproductive biology. Males of the orange mutant lacked any special preference for females of orange mutant. Inheritance of the orange mutant in mixed population showed its relative stability at about 21% from F2 to F8 generations. The utility of the orange mutant for studies on population genetics and dynamics of the cotton stainer is discussed.

A number of resistance sources have been identified against two major pests of sorghum, viz the sorghum shootfly, Atherigona soccata Rondani, and the stem-borer, Chilo partellus (Swinhoe). These identified sources of resistance were generally tall, late maturing and poor yielders. Two of these identified sources of resistance, viz. BP 53 and M 35-I, have been utilized in the breeding programme, by crossing with dwarf exotic types, which are highly susceptible to both the pests, but are agronomically desirable varieties. The crosses thus obtained were screened for their reaction to the two pests. An extensive screening programme was carried out under heavy levels of shootfly and stem-borer infestation from 1968 to 1980, which resulted in the identification of nine advanced generation derivatives possessing moderate to high levels of resistance to both shootfly and stem-borer as well as desirable agronomic characters.

The derivatives with M 35-I, as one of the parents showed more resistance to shootfly as compared to derivatives with BP 53, as one of the parents. However, in the case of resistance to stem-borer, the reverse was true.

Laboratory and field assays carried out so far indicate that microsporidian pathogens, especially Nosema spp., may be exploited for the management of the spotted stalk borer Chilo partellus and possibly other Chilo spp. Several formulations have been tested for the application of Nosema spores in the field for borer management. Significantly high levels of control were achieved when the pathogen was sprayed on plants infested with borer larvae, compared with unsprayed plots. Sublethal dosages of Nosema spp. reduced the biological performance of C. partellus, as indicated by reduced fecundity in infected females, high mortality in pre-imagines as well as in the filial generations, and reduced lifespan. There was also a high level of deformity in the surviving adults. Such debilitating factors would subsequently result in a reduction of population levels.

In sugar-cane pests, granulosis viruses have been observed to cause high natural mortalities in C. infuscatellus and C. sacchariphagus. Field infestation has been reduced by the application of the virus. Further, the presence of polyhedrosis viruses in C. partellus, and Chilo iridiscent virus in C. suppressalis, points towards the possibility of using this group of pathogens in Chilo control.

Studies were carried out on the neonatal development of Riptortus dentipes (Fabricius) and Nezara viridula (Linnaeus) on pods of cowpea Vigna unguiculata (L.) Walp (var. VITA-3) and soybean Glycine max (L.) Merrill (TG× 536–02D). Both crops sustained nymphal development and adult reproduction of R. dentipes. Nymphal duration was 20.7 days on cowpea and 21.3 days on soybean; mean adult weight was 56.3 mg (male) and 58.3 mg (female) on cowpea and 55.8 mg (male) and 57.6 mg (female) on soybean. Adults preferred soybean to cowpea for egg laying though a substantially higher number of eggs was laid on the mesh walls of the cages indicating the somewhat suboptimal nature of both plant substrates. The nymphal period for TV. viridula was 24.4 days on cowpea and 25.4 days on soybean, and the mean adult weight for males was 139.0 mg while that for females 186.0 mg on cowpea. On soybean, the mean adult weight was 127.3 mg for males and 176.9 mg for females. Soybean leaves were preferred for oviposition. The concept of host plant suitability to the various stages of these insects with respect to host switches between cowpea and soybean.

The insect growth regulator, 6′,7′-epoxy-3′-ethyl-7′-methyl-dec-2′-enyl 6-ethyl-3-pyridyl ether, at 10 ppm applied to rearing media, did not prevent oviposition or hatchability of the eggs of Tribolium confusum. The insect growth regulator (IGR) apparently had no effects on the development of younger larvae, and no morphological abnormalities were observed in these instars. However, the IGR prevented metamorphosis of the last larval instar. These larvae continued to moult several times, became larger than larvae in untreated food, but failed to pupate; as a result, no adults emerged from the treatments.

Correlations were established between an endemic infestation of the coffee margorodid, Icerya pattersoni Newst and the characteristics of the veins of the leaves it infested in four coffee species in Kenya. The attack was variable between species although there was an affinity for it to be confined to midribs of definite length and thickness and laminal veins of quantifiable dimensions.

Studies on losses in yield of rapeseed, Brassica campestris cv. Brown Sarson, caused by the mustard aphid, Lipaphis erysimi (Kalt.) were conducted under natural and artificial conditions. Based on the experiments on the influence of aphid exposure to the crop on aphid number and seed yield and the effect of varied aphid population at flowering/pod initiation stage and artificial release of aphids at 10-day intervals starting from 40 days of sowing on the plant height, number of siliquae per plant, number of primary branches, seed yield per plant and 1000-grain weight, a positive correlation between length of aphid exposure to the crop and aphid population was found. A negative relationship between aphid population, length of aphid exposure and seed yield was observed. An inverse and significant relationship existed between parameters contributing to yield loss and losses in seed yield. However, this relationship was not significant in siliquae per plant and 1000-grain weight. A similar relationship was observed in artificial infestation.

The influence of three cultivars of Sorghum bicolor (L.) on the activity of the fungus Metarhizium anisopliae on the stemborer Chilo partellus was investigated in the field and laboratory. Fungal activity in the field varied with the plant cultivar and the inoculum concentration. Larvae fed on different cultivars and inoculated with the fungus in the laboratory did not vary in their susceptibility to the pathogen. However, time to 50% mortality (LT50) of the larvae was shorter in cultivar IS 1044 than in cultivars ICS 3 and ICS 4. Compatibility of the fungus with cultivars is therefore an important consideration when using fungi for the biological control of stemborers.

Field and laboratory observations revealed that the placement of eggs of the sorghum shootfly, Atherigona soccata, among sorghum stems tended to be random or slightly aggregated rather than regular, which suggests that the site of oviposition by a female is little or not determined by the presence of other eggs already laid. The possible effects of this type of distribution on the mortality of the first-instar larvae are briefly discussed.

Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20–25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants. There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.

Herbivory by insects and mites on physic nut (Jatropha curcas L.) seedlings was investigated and compared with irrigation in the semi-arid Sahelian Niger, utilizing a randomized complete block design experiment. Three water treatment protocols were applied and the types of damage were recorded. Less than 5% of the seedlings died during the 10-month trial period with sap suckers causing the most damage on the surviving plants. Plants with high production of biomass and leaf cover (foliage) were most strongly positively correlated with irrigation and were also the plants that endured the highest degree of herbivory. The low dieback may indicate that defence mechanisms counteract seedling herbivory and that drought-stressed plants invest more in their defence mechanism system than vital plants.

The population patterns of eggs, larvae and puparia in the bean plants and leaf punctures made by adults were investigated during cropping (March–July and October–January) and noncropping (July–October) seasons at two sites in Kenya. The beans planted in noncropping seasons had more leaf punctures, eggs, larvae and puparia than beans planted in cropping seasons. Beans planted in noncropping season attracted unusually high population from surrounding weeds as well as previous crop which cause severe damage. Under field conditions Ophiomyia spencerella Greathead and Ophiomyia phaseoli Tryon were the species of bean flies infesting the bean plants in all seasons. Both O. spencerella and O. phaseoli normally oviposited in punctures on the leaves but O. spencerella also oviposited in the stems of bean seedlings.

Sorghum head bug, Calocoris angustatus Leth. (Hemiptera: Miridae) is an important insect pest of sorghum in the semi-arid tropics. A technique to screen for resistance to head bugs under field conditions was tested. Planting infester rows of susceptible cultivars (CSH 1 or CSH 5), 20 days before the test material or planting early (40–45 days) flowering lines (IS 802, IS 13429 and IS 24439) along with the test material, split planting of test material at 15-day intervals, grouping test material according to maturity, and use of sprinkler irrigation to maintain high humidity, were found effective in increasing the efficiency of screening and selecting for resistance to head bugs.

A headcage technique to screen for resistance under no-choice conditions has also been developed. Panicles infested with 10 pairs of bugs at pre- and half-anthesis, result in maximum population build-up and grain damage under headcage. This technique is useful for confirming the resistance observed under field conditions.

Under natural infestation, five genotypes harboured relatively lower head bug numbers than the susceptible checks, but only three (IS 17610, IS 17618 and IS 17645) maintained their level of resistance under the headcage. Seed germination was > 70% in these genotypes compared to < 10% in CSH 1 and CSH 5.

Investigations on the biology of Cinara cupressi, a voracious aphid of cypress trees in Kenya, showed that the aphid produced four nymphal instars within a fortnight under laboratory conditions of 22°C and 89% r.h. Reproduction was two nymphs per female adult per day for 12 days of reproduction. Nymphal multiplication was brisk, but was drastically countered by mortality which was highest in the first, third and fourth instars. This led to a mere nymphal survival of 11.0% at most under laboratory conditions.

A ‘rice garden’ with monthly plantings of rice was established in an irrigated lowland area in April 1993 and continued for 3 years. Populations of the most common insects, the stalk-eyed flies, Diopsis spp., and the green leafhoppers, Nephotettix spp., and spiders and stemborer damage varied distinctly in relation to month of transplanting. Arthropod populations also exhibited distinct patterns in relation to crop growth stage. Grain yields varied with month of transplanting but there was no distinct trend from one year to the next. This study indicated that continuous cropping of the same fields over a 3-year period did not result in a build-up of insect pests or a decline in grain yield.

There are 43 identified insect pests of sugar-cane in Mauritius, of which several are important enough to warrant control measures. However, insecticides are not used for this purpose. All the insect pests of sugar-cane are controlled biologically. This includes traditional biological control using parasites or predators, as well as more recent biology-based methods like the use of resistant cane varieties, sex pheromones, etc.

Mauritius has the distinction of being the first country on record to have successfully introduced a natural enemy, namely the Minah bird, specifically to combat a pest—the Red Locust, Nomadacris septemfasciata, in 1792.

Very few of the insect pests in Mauritius are indigenous; most of them are exotic, having been accidentally introduced into the country, one way or the other. Some of the important ones include: spotted stem borer (Chilo sacchariphagus), armoured scale (Aulacaspis tegalensis), white grub (Clemora smithi), white grub (Heteronychus licas), soft scale (Pulvinaria iceyi), armyworm (Leucania loreyi) and pink borer (Sesamia calamistis).

The introduction of various natural enemies from different parts of the world has been made over the years with different degrees of success. In all, there are presently a total of 102 species of parasites and predators controlling 43 species of sugar-cane insect pests.

With sugar-cane spread out over most of the island and representing 90% of all cultivated land, close vigilance over the important pest populations, and swift counter measures as appropriate, is required. This task is being performed efficiently and successfully by the Mauritius Sugar Industry Research Institute.

Studies on relative susceptibility of 78 citrus varieties/hybrids to the incidence of black citrus aphid, T. aurantii under tropical humid conditions in south India revealed that none of the varieties was completely free from aphid incidence. The varieties Nagpur Mandarin and Ikeda Unshiu among mandarins; Longsport Valencia, Campbell Valencia and Washington Navel among sweet oranges; and Carrizo Citrange a hybrid and Dessert Orange, Eureka Lemon, Grape Fruit Pink and Jatti Khatti, among acid citrus group, recorded significantly least mean number of aphids per flush and can be effectively used in breeding programmes.

The number of instars in the silkworm Anaphe venata was determined using three methods namely: (1) direct observation of cast exuviae by larvae reared through the entire larval stage, (2) use of frequency distributions of head capsule lengths and widths taken from larvae representative of the entire larval stage of the species and (3) morphological observations and examinations of larval segments and anal plates. Seven instars were observed for A. venata. The most reliable method was the direct observation of cast exuviae by larvae reared through the entire larval stage. It is further suggested that either the method of histograms of head capsules or examination of larval segments and anal plates be used to supplement this method for better reliability.