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.

Polyculture can help stabilize agroecosystems against frequent and severe pest outbreaks. An overview of the published data highlights ecological relationships among weeds, nematodes, arthropods, sugar-cane mosaic virus (SCMV), and the sugar-cane crop itself. Whereas individual studies commonly depict weeds as being either “good” or “bad”, this review is a synthesis of the variable roles and interactions of weeds in sugar-cane in order to provide a realistic perspective on the possibilities of weed interactions in sugar-cane agroecosystems. Conservation of weeds in Louisiana sugar-cane has resulted in more diversified arthropod fauna, higher natural enemy populations, and reduced damage by the sugar-cane borer, Diatraea saccharalis (F.). Weed competition and SCMV infection have each been associated with altered sugar-cane free amino acid accumulations that appeared to play a role in reducing populations of selected phytophagous nematodes. The combination of both weed and SCMV stress factors, however, have been shown to favour higher sugar-cane nematode populations. Although some weeds are alternate hosts for SCMV and its aphid vectors, and ratoon stunting disease (RSD), weed growth has not been linked with higher phytophagous nematode infestations or incidence of RSD. Weeds, if kept below economically competitive densities, may be ecologically and financially sound assets to sugar-cane pest management tactics.

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.

—A revision of the Neotropical species of the Forcipomyia squamitibia group, revealed three new species, F. (F.) catarinensis from southern Brazil, Colombia and Costa Rica, F. (F.) quechua from northwestern Argentina and F. (F.) rioplatensis from northeastern Argentina and northwestern Uruguay, which are described and illustrated. Forcipomyia (F.) squamitibia Lutz is redescribed from the original type material, a lectotype is designated, and F. (F.) soriai Wirth is recognised as a junior synonym. The remaining known species of this group are diagnosed, and keys to males and females are provided for the identification of the nine recognised species.

Insecticidal δ-endotoxins of Bacillus thuringiensis, Cry IA (a, b and c) were prepared from over-expressing cells of Escherichia coli and bioassayed against the third instars (6-day-old) of the spotted bollworm, Earias vittella Fabricius (Lepidoptera: Noctuidae), using artificial diet. The median lethal concentration (LC50) values were calculated for 6 days of exposure to δ-endotoxins. Cry IA(a) was found to be the most toxic (LC50 141.2 ng/cm2) followed by Cry IA(a) and Cry IA(b) with LC50 values of 224.5 and 300.5 ng/cm2 respectively. A highly significant reduction in larval weight took place in the surviving larvae treated with sub-lethal doses of the insecticidal crystal proteins.

Soil type selection for oviposition by gravid females of the armoured ground cricket Acanthoplus speiseri Brancsik (Orthoptera: Tettigoniidae), a pest of grain crops in Zambia, was investigated. Twenty randomly collected samples of different types of soil, each replicated five times in an oviposition choice tray, were made available to 20 gravid females maintained in an environmental chamber, and the number of egg pods deposited per soil sample recorded. Physical and chemical characteristics of each soil sample were analysed. Properties of the soil that served as important cues to soil type selection for oviposition by the gravid females were identified and used to develop a best subset regression analysis model, for use by farmers to predict egg pod numbers of the pest in soils collected from their crop fields. There were significant differences (P<0.05) in the mean number of egg pods deposited per soil sample. Acidic, loam, clay loam and sandy loam soils with a pH range of 4.41–6.62, were the preferred soil types for oviposition. The single most important soil quality that accounted for much of the variation observed in mean egg pod number among the soil samples was pH (adjusted r2=0.1152). This was followed by mineral composition, particularly of the elements K (adjusted r2=0.1084) and P (adjusted r2=0.0731). Characteristics of the 20 soil samples tested are presented. Impacts of interactions among the soil characteristics on mean egg pod number are explained and the procedure for using the developed predictive model by farmers in crop protection is discussed.

Prospects for the biological control of locusts and grasshoppers have become much brighter during the last ten years thanks to a number of international research projects. This paper examines a number of options, including one that is ready for immediate implementation: the mycoinsecticide, Green Muscle®, based on the fungus Metarhizium anisopliae (flavoviride) var. acridum. It has been registered in South Africa and other African countries are likely to follow during 1999. Trial results on grasshoppers and several locust species have been very encouraging, and preliminary tests on red locusts show potential as well. Recent research on pheromones also points to some interesting possibilities, both when used alone and in combination with a mycoinsecticide. Finally, microsporidian protozoans and rhabditid nematodes show some promise for long-term suppression of red locust populations, but more research and development is needed to demonstrate their potential.

Ten sorghum genotypes at three plant growth stages were evaluated for antibiosis component of resistance to Peregrinus maidis expressed in terms of survival, duration and population build-up of nymphs as well as longevity and fecundity of adults. Support of nymphal survival and continued succession in mortality was evidenced on IS 18676, IS 18677 and IS 19349, indicating the influence of antibiosis factor(s) which again was supported by their prolonged duration. The growth index was consistently low at three plant growth stages on IS 18676 and IS 19349, but the genotype, IS 18677 did not express consistency on 45 days old plants. Greater longevity of adult females over males was consistent at different growth stages. Low fecundity was predominantly noticed on IS 18676, while reduced longevity was pronounced on IS 18677 and IS 19349 which was reflected in low population build-up at 15 and 30 days after infestation, when infested with 25 or 50 neonate nymphs. All these parameters contributed together suggest that antibiosis levels in IS 18676, IS 18677 and IS 19349 proportionately increased with plant age and the variability at different growth stages may be attributed to the differences in host genotypes and greatly aid as potential donors in resistance breeding programmes.

The effect of covering post-harvest banana stumps with soil on banana weevil Cosmopolites sordidus (Germar) oviposition levels was investigated at three locations, Sendusu, Kawanda Agricultural Research Institute (KARI) and Ntungamo district of southwestern Uganda. In the first experiment oviposition levels were assessed in a banana system comprising growing plants and residues. Oviposition increased on sword suckers, reaching a peak 1–7 days after harvest and decreased thereafter. In the second experiment conducted on farmers' fields, corms received 70% of the eggs and pseudostems 30%. The area 5–10 cm below the collar received 27% of the eggs, the area 0–5 cm above the collar 30% and the area 5–10 cm above the collar 0.3%. The remaining eggs (43%) were laid 0–5 cm below the collar. The effect of stump height and covering the stumps was evaluated in both the wet and the dry seasons at Kawanda and Ntungamo. Cutting stumps to the ground level alone had no effect on oviposition. Covering post-harvest banana stumps reduced C. sordidus oviposition in the wet but not in the dry season.

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.

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.

The courtship behaviour of male Spodoptera exempta (Wlk.) has been quantified and used as a method of bioassay for the female sex pheromone. Virgin females become attractive to sexually mature males from 72 hr after emergence and henceforth their attractiveness increases gradually until they have mated. Mated females start losing their attractiveness to males gradually after mating and 72–96 hr after mating they cannot produce any courtship response in males. Amongst virgin females, crude pheromone-gland extract and synthetic pheromone compounds, it is the older live females and the crude extract at 0.1 female equivalent that produce highest responses in males. A certain degree of cross-attraction between three coexisting species has been noted, both by using live insects as well as synthetic pheromone compounds of these species under laboratory bioassays. Possible interspecific pheromone-related implications are discussed.

Biochemical approaches have been used to enhance the potency of Bacillus thuringiensis against Plodia interpunctelia. Tests were made with different classes of chemical compounds, characterizedby being safe, non-toxic to man, and cheap in price. Among the tested inorganic salts, calcium carbonate, calcium oxide and zinc sulphate were found to increase the potency of B. thuringiensis δ-endotoxin by 2.5-, 1.9- and 2.7-fold, respectively. With the nitrogenous compounds, the amino acids serlne, arginine, alanine and teucine enhanced the endotoxin effect by 52-, 3.6-, 13- and 1.1-fold, respectively. Also, among the protein solubilizing agents, EDTA and sodium thloglycollate led to a 100- and 2.6-fold Increase in the potency. Formic acid was highly effective among the organic acids used in enhancing the potency, followed by malk acid, with 4.8- and 2.4-fold increase, respectively.

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.

Malathion tolerance of the rose-grain aphid Metopolophium dirhodum (Walker) reared on the ancient wheat variety Emmer (Triticum dicoccum L.) was tested by topical bioassay and found to be lower than that of aphids reared on the modern more susceptible variety Marts Kinsman (T. aestivum L.). On both varieties, tolerance was greater at stem elongation than at the tillering stage of plant growth. All statistically significant differences when plants were treated with Cycocel and MCPA showed that the two chemicals, respectively, reduced and increased aphid tolerance to malathion, in keeping with the effects of the chemicals on induced plant resistance to aphids reported in the literature. Probit mortality slopes were not progressively altered by changes in LC50, so that similar differences in aphid tolerance to malathion were found at both LC59 and LC90 levels.

This short communication describes the morphological features of three specimens of Hyalomma truncatum which dropped off artificially infested rabbits in the laboratory.

A bioassay was developed to assess the in vitro feeding responses of Chilo partellus larvae to susceptible (Inbred A) and resistant (MP 704) maize varieties. Consumption of internode tissues from the two maize varieties differed while the reverse was true for the nodes. Aqueous extracts from the two varieties caused a decrease in feeding and weight gain, but these effects were more evident in MP 704 than in Inbred A treatments. This suggests that MP 704 has a water extractable factor affecting weight gain negatively. Dose-response curves of neural responses from the maxillary styloconica sensilla showed that aqueous extracts from the two maize varieties evoked different functional forms of impulse frequencies especially in the lateral sensilla. These observations suggest that the quality of gustatory stimuli in the two maize varieties differs.

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.

It has become increasingly noticeable that common features of many forest and forest/ savanna foci of West African human trypanosomiasis (WAT) are peri-domestic tsetse populations closely associated with domestic pigs. Recent evidence from various sources almost completely proves that, in at least some WAT foci, domestic pigs play an active role as reservoirs of Trypanosoma brucei gambiense. On the basis of this assumption, various aspects of Glossina palpalis and G. tachinoides local distribution and ecology, in relation to domestic pig and human populations, are discussed.

In those WAT foci where domestic pigs are kept, tsetse are widely distributed in forest islands, forest/plantations, and riverine forests, but major concentrations are in villages containing pigs. Close pig/fly relationships at the village level, involving peri-domestic feeding, breeding and resting behaviour on the part of flies, could be important factors in maintaining T.b. gambiense transmission in pig populations.

Endemic transmission of WAT to man could occur, either in villages where low pig densities dictate that a significant proportion of the fly population must also feed on man, or away from the village as a result of contact with infected flies which have strayed from a village transmission cycle.

The development of epidemic conditions could be explained, on the basis of changes in pig density and resultant changes in fly feeding behaviour. The sudden reduction of a pig population could result in an increased number of infected flies feeding on man, until such time as the fly population became stabilized on a reduced pig population (or on other hosts if pigs disappeared totally). During the period of increased feeding of flies on man, T.b. gambiense transmission could be intense.

Minor flare-up of WAT could occur if small numbers of infected pigs were introduced into a village area which had no previous history of pig husbandry. If a loose man/fly association persisted in such a village, endemic WAT could become a characteristic feature of that village.

Because of the fluidity of pig distribution and density, infected pigs could be instrumental in dispersing T.b. gambiense from village to village within a WAT focus and contribute to the persistent character of the focus. Pig movements involving much greater distances could also be important to the transfer of T.b. gambiense strains from one focus to another.