It is evident that our environment has been flooded with pesticides and that some of these have had effects other than those intended. There is no doubt that indiscriminate use of pesticides has the potential to upset temporarily many ecological patterns. Whether this is significant in the long run remains to be seen.

It is sincerely hoped that the experience of the past (especially in the first world) will ensure wiser use of the pesticides in the future (primarily in the third world). It is likely that new pesticides will be developed and that they will bring new problems. Some of these problems may have far-reaching environmental implications in terms of their potential benefits and their propensity for damage. These problems will be compounded by residues of pesticides and a host of other contaminants already present. Therefore, it should and must be everyone's responsibility that the potential benefits from pesticides are maximised. However, such maximisation will be realised only if the environmental implications of their use is understood, and if they are applied with discretion to minimise their side effects.

Hand-stinging and mass exposure methods of rearing the parasitoid Cotesia flavipes Cameron (Hymenoptera:Braconidae) on the stem borer host, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), were compared. The proportion of hosts successfully parasitised, progeny production, proportion of female progeny, and host mortality did not differ between the two methods. However, there was evidence of superparasitism of mass-exposed hosts. Releases of C. flavipes as adults and as cocoons were both effective methods for field colonisation of the parasitoid. A device for the release of C. flavipes in the cocoon stage is described.

Larval and adult predators comprise the largest component of the natural enemy fauna which attack the semi-aquatic rice caseworm Nymphula depunctalis (Guenée). Spiders, birds, and adult dragonflies/damselflies were the dominant predators of caseworm adults, while aquatic beetle larvae, aquatic bug nymphs and adults, and ants preyed on caseworm larvae. Egg parasitoids are unknown in nature and larval/pupal parasitoids are rare. A nuclear polyhedrosis virus, the only recorded pathogen, occurs but rarely. A ricefield pulmonate snail Lymnaea quadrasi (Mollendorff), which forages on algae, causes limited caseworm egg mortality in a passive and fortuitous manner. Water beetles—the dytiscid Cybister tripunctatus orientals Gschwendtner and hydrophilid Sternolophus rufipes Fabricius—are voracious larval predators. Prey consumption by these water beetles is higher on older caseworm larvae whose larger size creates more movement while the larvae are crossing the water surface. Also, older caseworms are more prone to leave the protection of their cases while under attack. Younger caseworm larvae, however, tend to retract and remain motionless when attacked. The last instar dytiscid preyed on an average of 11.4 caseworm larvae per day while that of the hydrophilid preyed on 6.7 larvae per day.

Field studies on oviposition site, preference and pattern of Busseola fusca on various stages of maize were conducted at Awassa (southern Ethiopia). The positions of egg masses in terms of leaf sheath and height from the ground were described for different ages of the maize plant. Irrespective of the age of maize plants, eggs were laid on the under side of leaf sheaths. Busseola fusca moths showed ovipositional preference to younger maize plants. Significantly fewer egg masses were laid on older plants (r=.0.98, P <0.001). A strong relationship between maize plant age and position of egg masses was found. During the post-tasselling stage the great majority of the egg masses were found below the primary ear.

The influence of host presence, age and mating on calling behaviour of the female spotted bollworm, Earias vittella, was studied under a 14L:10D photoperiod. Onset of calling was earlier in the presence of a host and 93% of the females initiated calling in its presence on day one after emergence, compared to 67% in its absence. A majority of the females initiated calling during the 10th hour of the first scotophase and thereafter the initiation shifted to earlier hours as age advanced. Females generally called longer in the presence of a host. The mean time spent in calling, from the 1st to the 10th day increased from 56 to 152 min in the absence of a host, and from 77 to 234 min in its presence. Most of the females resumed calling after mating, but the mated females exhibited a significant reduction in calling performance when compared with the virgin females.

Phagostimulant activities of sucrose, sitosterol, stigmasterol, campesterol, and soybean leaf extractables were evaluated towards the third-instar larvae of the cabbage looper, Trichoplusia ni Hubner (Lepidoptera: Noctuidae) on elderberry-pith discs under laboratory conditions. There was a linear relationship between sucrose dosage and larval feeding on the pith discs. Water fraction from PI 227687 soybean leaf extractables at dosages > 400 μg/disc inhibited feeding by T. ni larvae. Ethyl acetate fraction showed phagostimulant properties comparable to sucrose. Sterols (5 μg/disc) and soybean leaf extractables (40 μg/disc) in combination with sucrose (400 μg/disc) showed synergistic effect as phagostimulants. Implications of genotypic differences in sterol content in relation to host plant resistance are discussed.

A life table was constructed for the mustard aphid, L. erysimi during January, February and March corresponding to 14 ± 2°C, 16 ± 2°C, 20 ± 2°C and 74 ± 5%, 74 ± 6% and 54 ± 5% R. H. under laboratory conditions. The study revealed that the values of intrinsic rate of natural increase (rm) and finite rate of increase (λ;) were 0.1035, 0.096, 0.023 and 1.109, 1.101, 1.023 females/female/day. The doubling time (DT) was higher in the case of alate morph during March (13.088 days) than apterous morph during January (6.697 days) and February (7.220 days). On reaching the population at a stable age distribution, the nymphal population estimated was 84.36, 93.87 and 92.67 in January, February and March respectively. The life expectancy (ex) of newly born nymphs of L. erysimi declines monotonically with advancing of age in these months.

The leucaena psyllid, Heteropsylla cubana, was studied under constant temperatures ranging from 21.5 to 35.0°C. Total mean development time was 11.2, 9.6 and 8.1 days at 21.5, 25.0 and 30.0°C respectively. For these temperatures, the mean number of eggs laid was 532.3, 758.3 and 374.7 with hatch rates of over 90%. At 35.0°C, a mean of only 4.5 eggs/female were laid in 24 h, egg hatch (9.0%) was very low and nymphs did not complete their development. Nymphal survival was only 65% at 30.0°C, compared to 84.2 and 87.6% at 21.5 and 25.5°C, respectively. Adult longevity was highest at 25.0°C; females outlived males at all temperatures. Age-specific life table statistics are given for the three temperatures. The calculated intrinsic rates of natural increase (rm) at 21.5, 25.0 and 30.0°C were 0.226, 0.293 and 0.324 respectively. Relative humidities in the range of 25 to 84% did not affect egg hatching, nymphal survival, or adult emergence of H. cubana.

Callosobruchus maculatus (Coleoptera: Bruchidae), commonly known as the cowpea seed beetle, is the most important pest of stored cowpea in tropical Africa. In rural area where preservation techniques and facilities are limited, it causes post-harvest weight and quality losses. The importance of damages which can reach 100% in a few months justifies the development of effective and appropriate control methods in the villages. All these control methods and their applications are discussed in this paper. Chemical control is inappropriate at farm level, because of its cost and hazards. The many studies conducted on varietal resistance have enabled identification of varieties that are more or less resistant to this pest; however, the varieties are often of little interest from the agronomic point of view. The incorporation of that resistance in cultivated varieties is in progress. The physical control methods are inadequate because their application requires equipment and technical knowledge which are not found in rural areas. Biological control is an attractive alternative but is still at an experimental stage. All these limitations support promotion of traditional control methods. Among them, the use of inert substances as well as indigenous plants or their by-products have given, in many cases, a satisfactory control of C. maculatus.

Heterobeltiosis (relative to better parental variety) and standard heterosis (relative to standard variety) for 10 larval and cocoon quantitative traits among the hybrids between five multivotine and three bivoltine strains of silkworm, Bombyx mori L., were estimated. The results indicated that the hybrids between multivoltine females and bivoltine males gave higher heterosis than their reciprocals. Variance due to general and specific combining ability and the genetic components were also estimated. The role of gene actions governing the different traits studied is discussed.

In a comparative situation, the moths Plodia interpunctella (Hubn.) and Ephestia cautella (Wlk.) caused more damage in groundnuts (41.85% for P. interpunctella; 29.21% for E. cautella) than in maize, when these commodities were stored for 1 month in plastic jars. For maize stored for 3 months in plastic and traditional storage gourds, the weight losses caused by the moths were: P. interpunctella—15.48% in jars; 4.53% in gourds; E. cautella—20.68% in jars; 4.12% in gourds. Orange peel suppressed two-thirds of the populations of P. interpunctella and E. cautella at a dosage of 20.0g/100g maize. Neem leaves caused 100% mortality of P. interpunctella at 15.0g/100g groundnut and suppressed more than half the population of E. cautella at 5g/100g groundnut. The results show that the plant materials utilised have some insecticidal properties against P. interpunctella and E. cautella over a short period.

The effects of infestation and damage by the stalk-borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), were studied in the field on the grain yield of the following maize cultivare: Inbred A (susceptible), ICZ2-CM (resistant) and Katumani Composite B (a commercial early maturing cultivar). Borer infestation levels (egg-population density and larval-pupal population density) and damage levels (follar damage and stalk damage) were significantly lower during the long rainy season of 1984 than 1985. On Inbred A, oviposition by the moths during the pre-flowering and flowering stages was much more important in causing a reduction in the grain yield than that during the post-flowering stage of the crop. There was no correlation with grain yield on ICZ2-CM and Katumani. The larval-pupal population density on Inbred A (but not on ICZ2-CM or Katumani), had a significant negative correlation with grain yield. Follar damage and stalk-tunnelling by the borer only affected the grain yield of Inbred A. Under artificial infestation, the grain yield of Katumani is reduced significantly by the borer attack, but under natural infestation it escapes due to its early maturity. By comparison, ICZ2-CM has inherent resistance to C. partellus and infestation and damage by the borer have no effect on grain yield.

Experiments on artificial infestation of soybean with pod-sucking bugs showed that Riptortus dentipes caused more damage to the plant than did Nezara viridula. The density of four insects per plant used was high enough to significantly damage the plant. The reproductive developmental stages of the plant defined as R3, R4 and R5 were sensitive to the pod-sucking bugs studied. Plots infested with R. dentipes adults suffered 72% pod damage compared to 44% pod damage in plots infested with N. viridula. Riptortus dentipes significantly affected the physiology of the plant and reduced grain yield and grain quality. The results also showed that there is potential for biocontrol of pod-sucking bugs.

A simple method for the insecticide bioassay of liposcelids is outlined. The contact toxicity of five organophosphorus insecticides (OPs) and two carbamate insecticides (CBMs) was ascertained for Liposcelis bostrychophila and L. entomophila. Liposcelis entomophila was more tolerant to all the insecticides tested than the other species. Malathion was the least toxic OPs to both species, while chlorpyrifos-methyl was the most toxic insecticide tested against L. bostrychophila. These findings are discussed in relation to the infestation of these liposcelids in rice storages.

The present study deals with the interrelationship of the neuroendocrine complex (NEC) and male accessory reproductive gland (ARG) of a cotton bug, Serinetha augur. The NEC consists of brain (cerebral ganglia), corpus cardiacam (CC) and corpus allatum (CA). Based on the staining reaction of aldehyde fuchsin (AF) and chrom alum haematoxylin-phloxin (CAHP), four types of neurosecretory cells have been identified in the brain. The neuroendocrine control over the ARG in S. augury was investigated through ARG extirpation (andgonadectomy)-induced hypertrophy of CA. The changing pattern of proteins in the brain during the pre- and post-mating periods (as judged by electrophoretic investigations) further supports the interrelationship of the NEC and ARG.

Newly-deposited pupae Glossina pallidipes were incubated until emergence at constant temperature (20.5, 22.5, 25.0, 27.5, and 29.5°C) and compared with pupae held at ambient conditions (19 to 31°C). Egg follicles and enclosed oocytes of newly-emerged females were dissected and their lengths measured together with the lengths of the cutting blade of the hatchet cell of the right and left wings. Linear discriminant functions analysis showed that the mean length of egg follicle A accounted for 80% of the temperature-related variability. We therefore used a simple predictive equation for temperature experience based on mean follicle length in small batches of newly-emerged females. The equation predicted with reasonable accuracy the temperature experience of 19 monthly samples of newly-emerged G. pallidipes reared in an insectary under ambient conditions. Mean sizes of egg follicle A of the newly-emerged tsetse may therefore be of utility in estimating temperature experience of pupae.

The egg follicle C of the left ovary was developing first, indicating reversed ovarian sequences in 5.8, 4.8, 4.2, 2.2, 1.1 and 2.0% newly-emerged female G. pallidipes from pupae kept at 29.5 ± 0.5, 27.5 ± 1.0, 25.0 ± 0.5, 22.5 ± 0.5, 20.5 ± 1.0°C and then maintained at ambient temperature (19 to 31°C) in the local colony. There was a highly significant positive correlation between the frequency of reversed ovarian sequences in flies and temperature in the range 19.5–30.0°C. The incidence of the abnormality was very low (0.2%) in wild-caught females from the Lambwe Valley, probably reflecting the constancy of favourable temperatures in that location. Old females with altered ovarian sequence had apparently both normal pregnancy and alternate maturation of eggs between the ovaries. This appears to be the first report suggestive of a temperature-induced reversed sequential ovarian development in Glossina.

Species composition and behavioural patterns were determined for anopheline mosquito samples collected between October and September 1990, from Gambella region, south west Ethiopia. At least eight anopheline species, which differed in their habits, were found to be prevalent in the region. Findings of indoor-resting collection and hut density determinations showed the relative prevalence, in decreasing order of magnitude, to be Anopheles pharoensis, A. gambiae s.l., A. nili, A. coustani, and A. ziemanni. On the other hand, the relative frequency of occurrence based on outdoor human-bait capture was A. pharoensis, A. ziemmani, A. coustani, A. squamosus, A. paludis and A. funestus, in decreasing order of importance. The rate of human feeding of A. nili, A. gambiae s.l., A.pharoensis and A. coustani were 37.5, 33.0, 22.5 and 6.7%, respectively. Among the endophilic mosquitoes assayed, the overall infectivity rate was found to be 0.56%. Sporozoite rates of 0.77% for A. gambiae s.l. and 0.47% for A. pharoensis were determined.