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.

Thirty-five pearl millet cultivars of short, medium and long maturity cycle were screened in Senegal during 1985–1986 crop seasons to study field reaction to the attack of stalk borer, Coniesta (Acigona) ignefusalis Hmps.; spike worm, Heliocheilus (Raghuva) albipunctella De Joannis; millet midge, Geromyia penniseti Felt; head smut, Tolysporium penicillariae Bref; and ergot, Claviceps fusiformis Lov. Insect and disease incidence varied considerably depending upon cultivar maturity cycle. Least susceptible cultivars were IBV-8001 and P8 against spike worm; Zalla, NKK, P8 and M2D2 against head smut, and Ex-Darou against ergot. Cultivation of IBV-8001 has been suggested in northern and central Senegal. However, studies on identification and utilization of resistance sources of wide genetic diversity and multilocational tests may be necessary.

In two study seasons, viz. summer (March to May) and “kharlf” (August to October) 1984 at Bangalore, India, populations of Aphis craccivora Koch on cowpea increased rapidly with crop growth and their peak coincided with peak pod formation. The activity of predatory coccinellids started 1 to 3 weeks after the appearance of aphids. The peak predator population more or less coincided with the peak aphid population. Highly significant positive correlations were found between weekly aphid and predator populations in the two seasons. The prey to predator ratio reached higher values 2 weeks after the incidence of the aphid, during peak pod formation stage and at the time of harvest. Amongst the predatory coccinellids, Menochilus sexmaculatus (F.) was predominant in both seasons constituting 77–88% and 83–95% of total predator population during summer and “kharif”, respectively. The study demonstrated a prey-dependent predator growth, often lagging behind that of the prey, pressing the need for alternate control methods that can be integrated into the management strategy considering the weather factors such as rainfall.

A survey of the parasites, parasitoids and predators of the nymphs and adults of Oedaleus senegalensis showed that three dipterous insects and a red mite were common parasitoids of the grasshopper. Seven arthropod species were observed preying on the nymphs. Among the vertebrates, two reptile species, one amphibian and 20 species of birds were observed preying on both the nymphs and adults of the grasshopper.

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.

The damage threshold of the green spider mite, Mononychellus tanajoa (Bondar) on cassava was determined in the greenhouse using four levels of mite infestation namely: 5, 10, 15 and 20 adult mites per cassava plant. Cassava cuttings were planted in plastic buckets in the greenhouse. The plants were artificially infested at 10 weeks old after planting.

Visible symptoms of mite damage appeared on cassava leaves at 4 weeks after infestation and at this period, the average number of mites was found to be eight mites per leaf. The mean number of active stages of M. tanajoa (larvae, nymphs and adults) was highest at the infestation level of 20 mites per plant, followed by that of 15, 10 and 5, in that order. The mean number of eggs was also highest at the infestation level of 20 mites per plant.

Essential oil of sweetflag, Acorus calamus L. was fed (in artificial diet) to the variegated cutworm, Peridromo soucia Hubner, to assess its antifeedant and growth inhibitory effects. The oil decreased food consumption and larval growth in a dose-dependent manner in both neonate (first instar) and second instar larvae. Calamus oil applied to cabbage leaf discs significantly inhibited feeding by fourth and fifth instar larvae in a choice test. Nutritional experiments with fourth instar larvae using topical application or dietary exposure confirmed that sweetflag oil induces both antifeedant and growth inhibitory effects in Peridroma saucia, the latter possibly being independent of feeding behaviour.

Pure line populations of brown planthopper, Nilaparvata lugens (Ståi), are needed for identifying new genetic sources of resistance. Among the known N. lugens biotypes in the Philippines, Biotype 1 can infest rice cultivare which lack genes for resistance. Biotype 2 can damage cultivars carrying Bph1 resistance gene, in addition to those that are susceptible to Biotype 1. Biotype 3 can infest rice cultivars carrying bph2 resistance gene, in addition to those susceptible to Biotype 1. In the greenhouse Biotypes 1, 2, and 3 are maintained on TN1 (no resistance gene), Mudgo (Bph1 gene) and ASD7 (bph2 gene) rice plants, respectively. Because Biotype 1 population is reared on TN1 plants, susceptible to all the three biotypes, accidental infestations of Biotype 1, Biotype 2 and Biotype 3 cannot be ruled out.

N. lugens biotypes were separated from each other by their differential ingestion and assimilation of food on different susceptible and resistant rice cultivars. A homogeneous population of Biotype 1 of N. lugens was produced from single pairs of males and females selected on the basis of their low food intake on rice cultivars Mudgo and ASD7. The purity of such Biotype 1 population was further demonstrated for three generations based on differential nymphal growth and development and adult longevity and fecundity on resistant Mudgo and ASD7 and on the susceptible TN1 rice cultivars. The technique can also be useful in identifying biotypes of other sucking insect pests.

Cassava leaves damaged by green spider mite, Mononychellus tanajoa (Bondar) and undamaged leaves were analysed in the laboratory for chlorophyll content by spectrophotometry. Proximate analysis was also carried out on the leaves in the laboratory using the Association of Official Analytical Chemists methods.

More light was absorbed by the chlorophyll extract from the undamaged leaves than in the mite-damaged leaves. More light was also absorbed at the wavelength of 663 nm than at 645 nm. The concentrations of chlorophyll a and b were higher in the undamaged leaves than in the mite-damaged leaves. The concentration of chlorophyll a was higher than that of chlorophyll b both in the undamaged and mite-damaged leaves.

Mite-damaged leaves weighed less than the undamaged leaves, both when fresh and when dried. The proximate products values were less in the mite-damaged leaves than in the undamaged leaves.

Effects of topical application of two juvenile hormone analogues (JHAs), R-20458 (6, 7-epoxy-1(p-ethylphenoxy)-3, 7-dimethyl-2-octene) and ZR-512 (ethyl 3, 7, 11-trimetnyl-2, 4-dodecadienoate) on reproduction and longevity of mustard aphid, Lipaphis erysimi (Kalt.) were investigated. Doses of the JHAs as high as 2 μg per aphid failed to reduce the fecundity of the aphid though initial reduction in the daily reproduction was observed. Also, the doses which induced morphogenetic abnormalities at the third-instar, could not affect embryogenesis.

Spatial pattern of distribution of populations of three insect species, namely, Amrasca biguttula biguttula (Ishida), Bemisia tabaci (Genn.) and Aphis gossypii Glov. was studied in Upland cotton (Gossypium hirsutum L.) at an interval of 13–15 days during July, August and September in Punjab. The populations were found to be aggregated from the beginning of season upto 25 August in jassid nymphs, 12 August in whitefly adults and the end of season in apterous aphids. Environmental heterogeneity at low population in July and innate behaviour at high population were responsible for the aggregated dispersion in each of the three homopterans. Based on these observations the appropriate number of samples required to be drawn for population studies were determined which varied with change in pest density in each case.

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.

Evaluation of the use of food-dye marking method for the study of sandfly behaviour was carried out in Baringo district, Kenya. A solution of sucrose and food dye was sprayed as bait on the vegetation around a selected source of flies in an animal burrow.

The extent of marking and distribution of coloured flies within a radius of 200 m was monitored for four nights. The species caught were Sergentomyia clydei, S. schwetzi, S. antennatus, S. squamipleuris, S. bedfordi, S. africanus S. ingrami and S. affinis and the number of coloured flies was 1017. Feeding on the dyed solution labelled 68.9% of the exiting flies near the burrow and 49.2% of the flies caught at the burrow's entrance. The total number of coloured flies caught at a distance of 50, 100, 150 and 200 m was similar toa linear distribution. The greater numbers of S. clydei caught at 200 m and the smaller numbers of S. squamipleuris and S. ingrami trapped between 50 and 200 m deviated from this pattern. These results are discussed as well as the possible application of the method.

The effect of planting dates on beanfly infestation was investigated in successively planted bean plants during cropping seasons. The population tended to build up in the course of the season following the initial invasion by egg-laying females. Ophiomyia spencerella (Greathead) and Ophiomyia phaseoli (Tryon) were the species of beanflies infesting the bean plants in all seasons. The number of beanfly leaf punctures, eggs, larvae and puparia were more in late planted than early planted bean crop. The bean crop planted late in the season was severely damaged due to the generally higher population levels which had been building up in the course of the season.