Four groups of scientists were invited to participate in this Symposium, including those who have systematically studied or are still studying the relatively new problems of protozoal viruses of protozoa as inactivators of viruses and on protozoa as potential reservoirs of mammalian viruses would have presented itself.

Unfortunately, not all of the invited scientists could come to Nairobi. The most recent results of the Spanish group on protozoa as inactivators of viruses were not discussed (but see Programme and Abstracts of the Congress).

The midge, Contarinia sorghicola Coquillett, is a major pest of grain sorghum in many areas of Asia, Africa, Australia, Europe and America. Literature documenting the status of research on the biology, behaviour, and field and cage screening techniques is reviewed. Numerous germplasm entries have been evaluated and many resistant sources are identified from various midge screening programmes. A high degree of resistance was found in nine working groups viz., Caudatum, Durra, Caudatum/Nigricans-Zerazera, Caudatum/Kafir (Hegari), Nigricans, Caffrorum-Darso, Durra-Nigricans, Durra-Nandyal and Caudatum-Bicolor. The identified resistant sources and the midge resistant varieties released from the breeding programmes are listed. Studies on the mechanisms of resistance showed predominance of antixenosis for oviposition over adult attraction and variable degrees of antibiosis. The morphological characters and biochemical factors associated with resistance have been explored. Short and compact glumes which remain closed during anthesis conferred resistance. The tannin content in the ripening sorghum grain is related to resistance against the larva. The inheritance of resistance showed quantitative nature. The open and closed glume character expression indicated its dominance and recessiveness, respectively. Short glume character can be used as an useful genetic marker. Pedigree and modified pedigree breeding systems were suggested to transfer high level of midge resistance into agronomically acceptable types for selection and hybridization.

The biological hypothesis that female parasitoids can adjust their fecundity schedule according to host availability, and tradeoff longevity with fecundity was tested in a thelytokous oophagous parasitoid, Trichogramma brasiliensis Ashmead (Trichogrammatidae: Hymenoptera) parasitising the rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). The tradeoff between early and late reproduction revealed that this wasp was able to exploit practically all available hosts during the first day or first few days of adult life. During spells of host unavailability, it was able to adjust its fecundity schedule accordingly. There was a negative relationship between survival and reproduction. Adult females survived shorter (10 days) when an unlimited supply of hosts was present, but longer (16 days) when no hosts were provided. These observations suggest the potential suitability of T. brasiliensis for inundative releases even in conditions of fluctuating host availability.

Partial sterility induced by gamma irradiation of Ephestia cautella adult males was studied in five laboratory strains (A,B,C,D and E) which exhibit conspicuous genetic variation in the adult forewing pigmentation. Four of these strains had been reared in the laboratory for more than 80 generations, while the fifth strain has been reared for only 10 generations. When males irradiated with 0.2 kGy were crossed with untreated females, the per cent egg hatch was reduced significantly as compared to the unirradiated control crosses. Strain C showed the highest reduction in the per cent egg hatch followed by a gradual decrease in radiation sensitivity in strains A,E,D and B, respectively. Fecundity and mating frequency appeared not to be affected but the sex ratios were clearly distorted (about two males to one female) in all strains. F1 progeny of all strains were either sterile when mated together (per cent egg hatch = 0.0%), but semi sterile when F1 males were mated to normal females (per cent egg hatch = 0.03–3.95 %). Low fertility was observed when F1 females were mated with normal males (per cent egg hatch = 1.30–15.04%). The cytogenetical investigations showed spermatogenesis to proceed normally in the F1 males, whose fathers had been irradiated (0.2 kGy). However, the primary spermatocyte cells carried multiple chromosomal translocations which were the main cause of the sterility in the F1 males.

The American bollworm, Heliothis armigera Hüb. is the major cotton pest in Tanzania. The commercial cotton varieties have the ability to compensate for early loss of fruiting points caused either by physiological stress or by bollworm damage; and therefore early sowing, together with a blanket spraying regime, is recommended to minimize the damage caused by this bollworm. To extend this integrated approach, studies to incorporate Heliothis -resistant characters, viz. frego bract, nectariless, high gossypol and glandless into the Ukiriguru cotton varities, were started in the early 1970s and are still in progress. To date, frego bract has given consistently good results; and intensive work is under way.

Detailed biology of the sorghum earhead bug, Calocoris angustatus Lethierry was studied at Dharwad, India during 1979–1981. Egg incubation and nymphal developmental period ranged from 5.6–11.0 and 10.0–17.0 days, respectively. The duration of first, second, third, fourth and fifth nymphal instars was 2.2 to 3.4, 2.3 to 3.0, 2.0 to 2.8, 2.0 to 3.0 and 2.0 to 2.7 days, respectively. The males lived for 8.9 to 17.6 days and females for 12.2 to 21.3 days. Fecundity varied from 57.7 to 267.1 eggs per female. Preoviposition, oviposition and post oviposition periods varied from 1.2 to 2.1, from 7.2 to 14.0 and from 5.0 to 15.8 days, respectively. All the developmental stages of the bug are described.

The production of the nucleopolyhedrovirus (NPV) of the tobacco cutworm, Spodoptera litura was studied to determine the optimum conditions for in vivo production using homologous host larvae reared on artificial diet. We compared NPV production in 7, 8, 9 and 10-day-old larvae and found that 9-day-old larvae gave the highest virus yield. The optimum dose was determined by infecting 9-day old larvae (weighing 125–155 mg) with a range of doses. The maximum NPV production achieved was 3.91 × 109 polyhedral inclusion bodies (PIBs) per larva using an inoculum of 4.8 × 106 PIBs. A 7-day incubation period was found to be optimum for NPV production. Moribund larvae were found to be more suitable for handling and for the mass production of virus than dead ones.

The gelechid bud borer Anarsia achrasella (Latreille) has become an increasingly serious pest of sapodilla Manilkara zapota Van Royen in India. The objective of the present study was to estimate the pest damage potential and determine the influence of abiotic factors and plant phenology on the pest incidence. The results indicate that each larva of A. achrasella could damage up to 36.9–46.6 buds before reaching pupation. Correlation analysis indicates that the pest incidence is not influenced by plant phenology and that the effect of abiotic factors is minimal. Of all weather parameters studied, only minimum temperature and wind speed correlated significantly with bud borer infestation. The linear and non-linear analyses showed that, in the case of minimum temperature, polynomial model order (2) Y=0.4108x2−11.95x+92.329 was found to explain 46% of the variability in bud borer incidence. However, in the case of wind speed, none of the tried models could explain variability in A. achrasella incidence beyond 53%. The implications of these results are discussed.

Field trials were carried out for two seasons on the effect of insecticides on insect pests, damage and yield of three cowpea cultivars.

During the first season, the preflowering stage of crop growth was found to be infested by Aphis spp, Empoasca spp, Ootheca spp and Epilachna spp, the flowering stage by Megalurothrips sjostedti, Heliothis armigera, Astylus atromaculatus, Coryna kersteni and Mylabris amplectens and the postflowering stage by H. armigera and a number of coreid and pentatomid bugs. Fenthion gave the least protection against pod damage by H. armigera. There were significant increases in the number of harvestable pods per plant with insecticides. There were no significant differences in hull weight and shelling percentage. Grain yield was increased by 96.2 and 109.4% after treatment with dichlorvos and cypermethrin, respectively.

In the second season, cypermethrin and monocrotophos were most effective. Cypermethrin reduced the number of pod-sucking bugs by 58%, H. armigera by 93%, while monocrotophos reduced Empoasca spp by 39% and M. sjostedti by 79%. Cypermethrin reduced damage by pod-sucking bugs by 28%, and by H. armigera by 95%. Monocrotophos reduced damage by pod-sucking bugs by 14%, and by H. armigera by 80%. Significant increases in the number of harvestable pods per plant were obtained with monocrotophos and cypermethrin treatments. There were no significant differences between the number of seeds per pod, and the weight of 1000 seed-grains. Grain yield was increased by 55.4% after both cypermethrin and monocrotophos treatment. The application of these insecticides were financially beneficial but the gain was reduced when six sprays were applied. Cypermethrin and monocrotophos are promising insecticides for controlling insect pests on cowpeas.

Insect pests and plant diseases are among the main factors limiting bean production in Tanzania. A survey of methods of pest and disease management in small-scale bean production systems was carried out in Mgeta Division.

The results revealed that small-scale farmers are well informed of the major insect pests limiting bean production. The farmers know the type of damage caused by most insect species and the time of their occurrence. Although farmers are not aware of the pathogens affecting their crops, they can distinguish damage caused by insects from those due to diseases. Farmers are also aware that diseases are associated with environmental factors which influence disease development.

Farmers use both deliberate practices and incidental practices to manage insect pests and diseases.

The most frequently used deliberate practice is avoidance. Choice of growing season and date of planting are observed closely as a means of avoiding diseases. Although beans are cultivated in both growing seasons (September–December and February–May), the first season is the best for growing beans. Rains are not very heavy, but reliable and well distributed, and the season does not end up with low temperatures and high humidity which favour development of fungal diseases. Planting commences as soon as the rains start because early planted crops suffer less from pests. Farmers do not use purchased inputs in the form of fertilizer and pesticides. Larger insects are killed mechanically.

Incidental control takes place in the form of a number of cultural practices. Intercropping with maize, potatoes, cowpeas, pigeon peas, cassava or sorghum is normal and reduces the risk of crop failure. Terracing, where crop residues and weeds are buried under soil, reduces the amount of initial inoculum of certain pathogens. Farmers use a mixture of seeds of different cultivars deliberately, some high yielding and early maturing; and some late maturing, thus ensuring the farmer of food early in the season and beans as a cash crop later. Such variety mixtures appear to provide a buffer against pests and diseases.

A breeding strategy should be developed for variety mixtures instead of pure line varieties as the productivity of pure varieties in most cases is associated with the use of purchased inputs such as fertilizers and pesticides which are beyond the reach of small-scale farmers. Variety mixtures have a greater efficiency in using environmental resources, and are less affected by pests and diseases, and thus give higher yields than pure varieties.

Competition between Corcyra cephalonica (Stainton) and Ephestia cautella (Walker) was studied in broken cocoa beans using the two species alone, introduced one before the other and together. Both species of moths cannot co-exist for an extended period and in competition E. cautella becomes extinct. The results offer an explanation of recent evidence that C. cephalonica is rapidly becoming the most important pest of stored cocoa beans in Ghana today.

Varietal differences with respect to yield losses due to whitefly, Bemisia tabaci Genn. attack were observed at the “sooty-mould level” and “economic threshold (ET) level” of infestation. At the peak infestation level leading to sooty-mould development, the losses varied from 21.7 to 31.8% in boll numbers, 10.3 and 23.7% in boll-weight; 25.9 and 48.9% in seed cotton yield; 12.4 and 153% in seed oil and 29.4 and 66.5% in seed germination among the group of promising new cultures viz., LK 861, LPS 141 and L 389 and other group of commonly cultivated varieties viz., JKHY 1, MCU 5 and ADB 10050, respectively. Besides, the fibre qualities like length, strength, fineness and maturity were also found to be adversely affected.

Immature stages of five species of Gerridae are described and illustrated for the first time: Rheumatobates longisetosus Polhemus & Manzano, Rheumatobates probolicornis Polhemus & Manzano, Rheumatobates peculiaris Polhemus & Spangler, Telmatometra whitei Bergroth and Telmatometroides rozeboomi (Drake & Harris). The first two were distributed in the Pacific region of Colombia, R. peculiaris distributed along the Pacific region of Colombia to Ecuador, T. whitei distributed from Mexico to Colombia and Ecuador, T. rozeboomi from Central America to Colombia and Ecuador. The five species were collected in the southwest of Colombia, near the Pacific coast.

Environmental characteristics (for example, temperature, photoperiod) as seasonal cues can affect the offspring sex ratio and reproductive tactics of many hymenopteran insects. Leptocybe invasa Fisher & La Salle is the most critical invasive insect pest of Eucalyptus spp. in the world and displays thelytokous reproduction. In the current study, we studied the effects of temperature and photoperiod on offspring sex ratio and reproductive tactics in L. invasa. Results show that sex ratio (female: male) of L. invasa was under 15, 25 and 35 °C with both L 12: D 12 and L 16: D 8, and cold and thermal acclimation were 74.5:1, 71.0:1, 59.0:0, 17.3:1, 53.0:0, 64.0:0, 47.0:1 and 56.0:0, respectively, which was highly significantly female biased and with no significant difference due to temperature or photoperiod. Offspring virgin females oviposited and induced the bump-shaped galls on plants under the same conditions as described above. Constant temperature, photoperiod and their interaction, and cold and thermal acclimation had no significant effect on the infestation rates of Eucalyptus branches induced by offspring virgin females. Thus, temperature, photoperiod and cold and thermal acclimation did not influence female-biased sex ratio and tactics with thelytokous reproduction of offspring females in L. invasa.

Flight activity in strain 16cSS of Anopheles gambiae (sensu stricto) has been investigated using an acoustic actograph. The peak activity was concentrated within the first hour after light off. After recording their activity, individual mosquitoes were examined for their chromosome inversion karyotype. No significant relationship was found of any of the karyotypes to total activity over the 2 hr after light off or the time at which 50% of their activity had been completed.

The results are discussed in relation to the possible widespread introduction of mosquito bednets and the possible selection of mosquitoes biting abnormally early before people go to bed.

The effect on the larval development of Helicoverpa armigera of caffeoylquinic acids and their structural units, caffeic acid and quinic acid, was evaluated. 5-Caffeoylquinic acid (5CQA) (syn. chlorogenic acid) significantly retarded larval development and increased the number of days to pupation at a concentration of 9 mM in an artificial diet, although final pupal weights were not severely affected. Caffeic acid and quinic acid also inhibited larval development although their effect was less marked. In all cases the effect of the compounds was dose-dependent. A mixture containing 5CQA, 3-caffeoylquinic acid (3CQA) and the novel compound, 1-caffeoyl-4-deosyquinic acid (ICdQA), which were extracted from the wild groundnut species, Arachis paraguariensis (Chod et Hassl.) was also evaluated at a concentration equivalent to that found in the plant (9 mM). This mixture was a potent inhibitor of larval development and more potent than 5CQA alone at the same concentration. The potential role of these substances in host plant resistance of groundnuts and their interaction with other components of pest management strategies are discussed.

The leaf-eating caterpillar, Opisina arenosella Walker, is the most destructive pest of coconut palm in India and Southeast Asia. The management practices employed against O. arenosella so far have been unsuccessful in many instances in India, due to the pest behaviour and coconut palm phenology. The life cycle, incidence and behaviour of O. arenosella are rather interesting and useful for the intervention of pheromone trapping technique for its management. We conducted the present study with the intention of identifying the female sex pheromone of O. arenosella and testing its efficacy under field conditions. Gas chromatography coupled electroantennographic detection (GC–EAD) and gas chromatography–mass spectrometry (GC–MS) analysis of female pheromone glands extract of one-day-old O. arenosella females confirmed the presence of (Z,Z,Z)-3,6,9-tricosatriene (Z3Z6Z9-23Hy) as the dominant sex pheromone component. The male antennal response to female pheromone gland extract and synthetic Z3Z6Z9-23Hy was recorded using GC–EAD, and the results revealed that antennal response was positive to both the treatments at 0.13 mV and 0.14 mV respectively, compared to control (air), which was 0.016 mV. It was also evident from wind-tunnel experiments that the male moth response was high (80%) with the female gland extract, compared to 60% with synthetic pheromone and 0% for control (air). Male moths caught in the traps with and without lure were assessed in two field sites and recorded 69.26% and 54.25% more moth catches in the traps with the lure. We also observed a similar result in the cage experiment in which male moths caught in the traps with and without lure were 64.50% and 12.40%, respectively. The study also confirmed that 93.20% moths caught in the pheromone-baited traps were male. From the study, it is evident that the presence of (Z,Z,Z)-3,6,9-tricosatriene, which is the sex pheromone compound from the female gland extract of O. arenosella, is an effective attractant in pheromone traps for the male moth under field conditions.

Diversity amongst the different populations is one of the problems in the control of medically important mosquitoes. Wing morphometry was used to identify within-species variation amongst some populations of Aedes aegypti in three areas of Lagos State, Nigeria. Ten landmarks on the right wing of adult female Ae. aegypti mosquitoes were digitized using TPSdig software. Relative distances of the veins and interpoints were calculated as well as the Euclidean distances based on these relative distances. In three (50%) of the interpoints, the relative distances were significant (P<0.05) to both the Brown–Forsythe F ratio and Welch ANOVA. The highest Euclidean distance of 7.738 was between Ebute Metta 2 and Badagry; the lowest of 4.426 was between Ikorodu and Ebute Metta 2. The distance between Ebute Metta 1 and Ebute Metta 2 was 5.867, which is more than the distance between Ebute Metta 2 and Ikorodu. Three groups of Ae. aegypti were identified, and the differences in lengths and interpoints observed on the wing veins suggest a possible morphological divergence amongst populations.

Polyphenism is a common feature in the mustard aphid, Lipaphis erysimi (Kalt.) in tropical countries. The function related changes in basic biochemical pool are reported during development of polyphenic forms. A gradual decrease in the protein content in this aphid was recorded, as the nymphs advanced in their instar number and reached adult stage. However, the protein content was significantly lower in the apterous forms as compared to alate. The number, density and mobility of protein bands varied as the nymphs passed through different instars and the number of bands was more in alate forms. The glycogen and trehalose contents showed a decrease upto the third instar and showed an increase in the fourth instar, but again declined in the adults of both the phases.

Larval instars of Chilo partellus Swinhoe reared on sorghum plants were determined. The larvae were separable into five non-overlapping instars by analysis of variance and Duncan's multiple range test, frequency distribution and scatter diagram of the head capsule widths. Head capsule increment from one instar to the next conformed to Dyar's rule, while at the same time agreeing with Richards' hypothesis. The stadial periods for the five instars were 6, 4, 5, 3 and 7 days, respectively.