The present article considers quantitative assessment of crop losses in relation to attack by three trophic levels of insect pests on maize, cowpea and sorghum intercropping systems. The trophic levels considered are (i) specialist feeders subsisting only on one crop within the intercropping systems, e.g. Maruca testulalis (Geyer) on cowpea, and Atherigona soccata (Rondani) on sorghum; (ii) the relative specialist feeders subsisting on two out of the three crops e.g. Busseola fusca (Fuller), Chilo partellus (Swinh.) Sesamia calamistis (Hmps.) and Eldana saccharina (Wlk.) feeding on maize and sorghum cereal plants; and (iii) the generalist feeders e.g. Heliothis armigera (Hbn.) which feeds on all three plant species. Tests for loss assessment were done under natural field conditions within maize, cowpea, sorghum monocropping patterns; maize–cowpea, maize–sorghum, sorghum–cowpea dicropping patterns; and the maize–cowpea–sorghum tricrop intercropping patterns. The authors discuss in detail their modified analytical methods based on the comparison of yield of sets of plants growing under identical conditions except that one set is unattacked by the stem-/pod-borers and the other set attacked, to generate economic losses. The comparative advantages of the planting systems on crop turnover is further discussed. The biomass and plant population fluctuations caused by pest attacks and ‘dead hearts’ at differential time scales in indices of yield have also been discussed. Yield per unit area of monocrop and intercropping patterns have been contrasted using the yield turnover of monocrop plant equivalence as the baseline for comparisons. Maize–cowpea–sorghum mixed intercrop of 1.45 land equivalent ratio (LER), and that for the sorghum–cowpea dicrop with 1.3 LER are considered the most advantageous cropping patterns. Yield losses significantly higher (P < 0.05) within maize-sorghum intercropping combinations with 0.89 LER further suggests that stem-borer colonisation which occurs at an earlier stage of crop establishment resulting in ‘dead hearts’ and significant reduction on plant population per unit area within the two cereal combinations contribute significantly to the overall reduction in crop turnover within such mixtures.

The functional development of the accessory reproductive glands (ARGs) and that of the corpora allata (CA) in the male grasshopper, Cataloipus cymbiferus, appear to be correlated. The growth of the ARGs and that of the CA glands increase with age to a maximum, 20 days after adult emergence. The increase in size of CA cells suggests increased secretory activity. However, the administration of farnesol, a juvenile hormone analogue, does not appear to have any direct effects on the growth of ARGs, although it completely blocked the growth and secretory activity of the CA.

The paper which covers a two season study from 1981 through 1982, major and minor cropping seasons, describes an improved methodology of sampling for stem-/pod-borer pests within an intercropping farming system involving maize, cowpea and sorghum as target crops. The authors' approach to the intercropping study has been from a holistic angle in an attempt to gain an understanding of the processes which lead to intercropping advantages under the different cropping patterns. The target pests reported were categorized into three trophic levels: firstly, specialist feeders which were Maruca testulalis (Geyer) on cowpea and Atherigona seccata (Rondani) on sorghum; secondly, the relative specialist feeders as Chilo partelhts (Swinh.), Busseola fusca (Fuller), Eldana saccharina (Wlk.) and Sesamia calamistis (Hmps.) on maize and sorghum; and thirdly the generalist feeders represented by Heliothis armigera (Hbn.) which subsists on cowpea, maize and sorghum plants respectively. The entomological data assayed included levels of borer attack on plant spatial and temporal patterns. The population of C. partellus, the dominant stem-borer within the study area was significantly regulated within the intercropping systems. The borer incidence on the maize and sorghum monocrops and the maize/sorghum dicrop was earlier (>14 days after germination, DAG) and accentuated with time, whereas intercropping of the cereals with non cereals caused significant delay (>42 DAG) in the borer colonisation and establishment within the intercropping systems. Incidence of ‘dead hearts’ caused by the borers was significantly higher (P < 0.05) within sorghum than maize stands; a factor related to the significantly higher borer attacks on late tillers which suggest that plant ventrical heights within stands influenced borer attacks. Sorghum shootfly was restricted to within 42 DAG and very much regulated by intercropping. Maruca testulalis attack on cowpea plants was confined between 30 through 60 DAG of cowpeas. Presence or absence of non-preferred cereal hosts within the cropping patterns did not seem to interfere with the M. testulalis colonisation and establishment processes within the cropping patterns. Pod damages resulting from Maruca attack were however influenced by the cropping patterns with mixed maize–cowpea–sorghum intercrop, producing significantly higher healthier pods. The paper concludes that some intercropping patterns have many advantages over monocropping patterns with respect to pest colonisation and establishment.

Incidence and extent of damage resulting from attack by the striped bean weevil Alcidodes leucogrammus Erichs, were assessed by random sampling of cowpea plants in monocropped and within maize-cowpea-sorghum intercropping combinations at two locations. The biology and damage symptoms caused by the bean weevil are discussed. The effect of A. leucogrammus incidence on cowpea nodulation is evaluated and evidence presented that the weevil attack causes a reduction in the number of nodules. Emma 60, a local cowpea cultivar, exhibits some degree of resistance against A. leucogrammus (P < 0.05). Sorghum–cowpea intercropping combinations have significantly fewer weevils (P < 0.05) possibly as a result of the close spacing and tillering capacity of the sorghum companion crop which prevents or obstructs the weevil migration between rows.

The composition and preparation of a general purpose artificial diet for rearing insects is described. Forty-one species were reared for one generation or more, and 56 species were partially reared or maintained on this diet. The advantages and applications of using a single diet for multiple-species rearing are described.

The diet is economical (NZ $2.37 per kg) for general laboratory rearing. In freeze-dried form it can be used for bioassays of pathogens, pesticides, insect growth regulators, plant resistant chemicals and other toxins, and has a potential market in the development of insect rearing kitsets for educational purposes.

Two types, wood and pod nest, were distinguished for Cataulacus guineensis in a Ghanaian cocoa farm. The contents of the nests were examined over the year, and the importance of the various inquilines in the nests is discussed. The termite, Neotermes spp. was found to actually initiate wood nests of Cat. guineensis. Heads of adults of the various castes were measured for comparison. The indication was that generally no significant differences exist between the sizes of the ants. The structure of the nest and the distribution of the brood within the nest were also investigated. The brood are almost uniformly distributed throughout the nest.

This paper discusses the effects of some controllable aspects of annual cropping systems on several components of insect pest occurrence. The components of cropping systems include spatial and temporal diversity at the farm level. Some effects of these factors on pest colonisation, numerical increase, emigration, damage, and carryover to future crops are illustrated and discussed. Examples of how cropping systems affect specialist and generalist insect pests are also given. Finally, the effectiveness and practicality of controlling insect pests by manipulating cropping systems is considered. Intercropping appears most likely to reduce insect pest occurrence under general conditions, however the need to manage several different crops simultaneously can present some constraints.

The susceptibility of 23 cotton genotypes to spotted bollworm, Earias vittella, was studied under natural infestation during 1977 and 1978 rainy season at Delhi, India. There were substantial differences in bollworm damage and larval population in different genotypes. Damage in shed squares and bolls was higher than in green bolls picked up from the plant. The damage/larval population in the less susceptible cultivars (Hindiweed, XG-15, HR-26 # 8XH · HG-6-IN and Sanguineum) was lower than in the susceptible check (BJR) and the trial mean. The differences in susceptibility were more pronounced at the moderate damage levels and that the damage in less susceptible cultivars increased or decreased according to the insect pressure.

There were significant differences in the gossypol, tannins, moisture, phenols and sugar content among the genotypes tested. Gossypol, tannins and moisture content of bolls and squares were negatively correlated with bollworm damage and larval population. Free phenols showed negative, but lower correlation coefficients with bollworm damage. Sugars contributed towards susceptibility while nitrogen content of bolls did not show any effect on bollworm damage. The less susceptible cultivars had higher amounts of gossypol and tannins. Some genotypes showed ovipositional non-preference because of smooth leaves.

Many factors appeared to influence the genotypie susceptibility to spotted bollworm, of which gossypol, tannins and ovipositional non-preference (due to smooth leaves) were the major factors. Gossypol and smoothness are genetically inherited and can be manipulated through crop improvement. The rating of the number and size of pigment glands on the calyx tubes and hairiness on the under surface of leaves can be used as important marker characters in breeding for spotted bollworm resistance.

Late third stage (7-day-old) larvae and 1-day-old pupae of Anastrepha suspensa Loew (Diptera: Tephritidae) were dipped for 5 min in suspensions of 25% WP Dimilin® (diflubenzuron) at six dosages ranging from 0.003–0.1% a.i. Diflubenzuron caused significant (P < 0.05) mortality during the pupal stages of both groups treated. Consequently, the resulting adult populations were drastically reduced. The incidence of crumpled wings, deformed abdomens and ovipositors in these adults was 2–7 times and 4–9 times higher than the respective controls of treated larvae and pupae. The morphological abnormalities altered mating competitiveness of males and successful copulation and oviposition by females. Fecundity of females was reduced and diflubenzuron effects persisted into the first generation and caused decreased egg viability.

Adults fed a 0.1% a.i. diflubenzuron-treated diet for 27 days had no significant mortality, but had decreased fecundity. However, their pattern of oviposition did not differ from the control. Fecundity levels similar to the control's were achieved 6 days after the treated diet was replaced by normal diet. Diflubenzuron treatment of adults also drastically decreased the survivorship of first-generation individuals between egg-hatch and pupation. However, almost all individuals that pupated emerged as adults. No abnormalities were observed in first-generation adults or in the survivorship of their offspring.

Survey and experiments were conducted to investigate the distribution and bionomics of the rice stem-borers in Kenya. Stem-borers collected and identified included: Maliarpha separatella Rag., Diopsis thoracica West, Sesamia calamistis Hmps. and Chilo partellus Swin. Maliarpha separatella were most abundant and infested throughout the crop season, D. thoracica infested during vegetative phase. S. calamistis frequently occurred at the onset of flowering stage toward harvest. C. partellus occurred more frequently in upland than lowland rice and was at low population. Assessment of crop loss caused by M. separatella was carried out under field, caged condition. It was observed that the per cent of empty grains was affected by Maliarpha infestation. Calculated yield loss based on percentage empty grains and number of ‘whiteheads’ was higher than the actual differences between grain weight of uninvested and infested crops.

The oviposition behaviour of spotted bollworm, Earias vittella Fab. was studied on 23 cotton genotypes under field and laboratory conditions. There were substantial differences in the number of eggs laid on different genotypes. More eggs were deposited on the bolls compared to leaves and squares. The relative oviposition preference differed under the field and laboratory conditions in the case of some genotypes. Leaf hairiness was significantly and positively correlated with number of eggs laid both under field and laboratory conditions. The effect of oviposition on varietal susceptibility appeared to be modified through other factors, such as gossypol and tannins. However, oviposition non-preference was one of the important resistance mechanisms in some cotton genotypes.

The studies show that the population of Maruca testulalis fluctuates greatly between the long and short rainy season and is significantly lower during the short and dry season, even when the cowpea crop is maintained under irrigation conditions. Studies on larval and pupal populations at Mbita Point, in Western Kenya and related farmers' plots showed lower populations under pure cowpea than under cowpea-maize intercrop, especially at 50% cowpea flowering stage (i.e. the second sampling stage). Although this difference was consistently manifested in the three seasons of experimentation there was no significant difference in larval population and extent of flower damage. Studies using three susceptible cowpea varieties (Ex-Lwanda, TVX 66-2H, and TVX 1193-059D) showed no significant difference in larval, pupal and adult populations when unsprayed. However, when sprayed with dimethoate (Rogor E 40) a systemic insecticide, significantly higher larval population was obtained in TVX 1193-059D, which shows the most vegetative growth of the three varieties. The borer damage on the flowers was not significantly different in all varieties under both the sprayed and unsprayed conditions. Studies using assessment of the different larval instars of M. testulalis in both sprayed and unsprayed conditions showed a continuous infestation of the crop throughout the season unless pod and flower production ceased. The fourth and fifth instar larvae were more abundant in pods than in flowers of the cowpea plant.

Field observations were carried out on a natural outbreak of a nuclear polyhedrosis virus of the armyworm Spodoptera exempta. Records were kept in four study sites with varying larval density, vegetation cover, and climatic conditions. Biotic factors influencing disease outbreaks were also noted. Initial mortality was recorded 11 days after larval outbreak, and the highest mortality occurred 10 days later. The epizootic was highest in sites of high larval density, wide fluctuations of daily temperatures (range 16.2°C), and high relative humidity. Rainfall was recorded in all disease outbreak sites. An acridid Acrotylus patruelis fed on larval cadavers in the field. Polyhedral inclusion bodies recovered from the gut of A. patruelis caused disease when fed to third instar S. exempta larvae in the laboratory. Predation on larvae by the pied crow Corvus albus in some observation sites reduced larval numbers, and may have prevented NPV from rising to epizootic levels in such areas. In sites of high polyhedrosis incidence, the disease led to larval population collapse in 3 weeks following disease outbreak.

A model for mass-rearing of tropical crop-borers has been developed using Maruca testulalis as a case study. Maruca testulalis (Geyer) (Lepidoptera: Pyralidae) has been reared from egg to adult for three generations on artificial diet at laboratory room temperature ranging between 25−30°C with a 12-hr photoperiod. The total life cycle was completed in 23 days. Average life data from the three generations reared on diet are larval period (13.35 days), pupal period (6.67 days); pupal weight (52.69 mg) for female and (49.68 mg) for male; survival to adult 60.3%; fecundity (257.1) eggs per female.

A number of butadienes and their thiophene congeners were found to be phototoxic toward the larvae of the mosquito Aedes aegypti and of the fruit fly Drosophila melanogaster. Only the first instar larvae of the fruit fly were killed by the chemical treatment in the presence of long wavelength ultraviolet light (UVA), while the mosquito larvae were all affected by a similar treatment which was performed with either UVA or natural daylight. With one exception, the mosquito larvae were all killed within 1 hr of daylight exposure in the presence of an average concentration of 0.8 ppm of the phototoxin. The fruit fly larvae were killed within 20 min of exposure to UVA when in contact with a filter paper disc containing 1.13 × 10−5 g/cm2 of the phototoxin.

An extensive survey for natural pathogens and parasites of mosquitoes as prospective biological control agents was carried out in Israel. Coelomomyces (Class, Chytridiomycetes; Order, Blastocladiales), a fungal genus of which all but a few members are specific to mosquitoes, was not known to be present in Israeli waters. Therefore, mosquito and copepod host-range tests were conducted with Coelomomyces psorophorae obtained from abroad, in order to test the desirability of introducing Coelomomyces as a contribution to mosquito control. Acanthocyclops viridis, a cosmopolitan copepod relatively common in Israel, was duly infected with Coelomomyces psorophorae. However, the infectivity of Israel's most common pest mosquitoes (Culex pipiens complex) proved low.

Preliminary studies were conducted using four varieties of potted cowpea (Ex-Luanda, Katuli 107. Vita 1, TVx66–2H) to determine plant response to injury to foliar and reproductive structures. Several levels of leaf loss were simulated at two plant growth stages; flowers were excised manually for 10. 15 and 20 consecutive days post-flowering; and pods were removed at several levels, 7–10 days after flowering. Similar tests were carried out during the short rains of Mbita Point Field Station (MPFS) and on a farmer's field at Kodiera, near Homa Bay, using two varieties—a local indeterminate dual purpose type (Ex-Luanda) and a determinate grain cultivar (TVu 1509). Defoliation significantly decreased plant weight and pod and grain production, but not branching and pod dimensions of potted plants. Flower and pod loss did not markedly lower plant weight, pod and seed production, and the effect on branching was negligible. The response of field plants was strongly influenced by crop variety and environment, notably agronomic practices and location. These results have implications for integrated pest management (IPM) which are explored in the context of increased grain legume production.

Field plots and cage experiments were conducted to study the effects of intercropping sorghum, millet and maize on infestation by the most important lepidopterous stem-borers of the three crops. Intercropping was done both within and between rows. The highest number of B. fusca eggs were deposited on sorghum, followed by maize and least on millet, among the sole crops. The number of eggs found in the crop mixtures was intermediate between the numbers obtained when the crop components comprising the mixtures were considered as sole crops and averaged. The inability of B. fusca adults to effectively utilize millet for oviposition, reduced larval infestation of sorghum stems when interplanted with millet. The best combination was millet interplanted with sorghum in alternate stands within the same row. The millet stem-borer, A. ignefusalis also showed definite preference for millet, but infestation on millet did not seem to be affected by intercropping with either sorghum or maize.