Four pest control models which combine sterile releases with trapping are analyzed. The traps are baited with either female sex pheromone or food and may contain either insecticides or sterilants. The efficiency for control or eradication is greater when control methods are used in combination than when either control method is used in isolation. The most efficient combination for pest species with high fertility rates is the release of steriles together with the use of pheromone traps containing sterilant. For pest species with very low fertility rates and high survivorship, such as tsetse, sterile releases combined with food traps containing insecticides are most efficient.

Adding a dye, Calco Oil Red N-1700, to the larval diet of Chilo partellus has been shown to be a useful method for marking the moths for mark and recapture experiments. The method is time-saving and the dye is safe to handle; marked insects and their egg batches are easy to detect. Insects reared on dyed diet did not show any differences in development time or pupal weight compared with insects reared on normal diet.

Role of trichome density in cassava resistance to mealybug, Phenacoccus manihoti Matile-Ferrero was evaluated on the apex, the first expanded leaf and the stem in pubescent and glabrous cassava varieties. Pubescence significantly retarded the rate of settling and establishment of P. manihoti. The weight of the developing larvae was also affected becoming more pronounced at the pre-ovipositing adult stage. However, the relationship between pubescence and P. manihoti weight was not significant. Moreover, the significant differences in weight at the preovipositing adult stage was not reflected in the corresponding fecundity on the glabrous and pubescent varieties. Pubescence accounted for only 18% of the differences in observed fecundity. There was also no significant difference in the development period of the mealybug on glabrous and pubescent varieties. Pubescence appeared to be a mechanical irritant only.

Three generations of the maize stalk borer, Busseola fusca (Fuller) per year were observed in maize fields in Southern Ethiopia. However, the third generation was not important on maize. The first generation developed on young maize plants during the wet season (April–July). The second generation occurred in July and majority of larvae went into diapause from September to February while a small proportion pupated in the months of September and October and gave rise to a third generation. Pupation of the diapause larvae was observed in April.

Female moths from the first (non-diapause) generation laid significantly more eggs than those coming from a diapause generation. Longevity of these moths was also significantly longer than the diapause generation. Despite the indicated differences, female moths from both generations laid most of their eggs between the second and fifth nights after emergence. The number of eggs laid and rates of hatching declined with age of moths irrespective of generations.

The effects of applying varying doses of an antibiotic to fifth instar larvae of Philosamia ricini on the silk glands were studied. Transaminases were increased by low doses, while RNA accumulation was reduced after administration of tetracycline. The levels of DNA showed little response to treating with antibiotic. However, the incorporation of amino acids into silk proteins was generally increased. The overall effects on the silk gland was reflected by its weight, cocoon weight, quantity of raw silk and quality of silk. All these indices were improved by administration of tetracycline.

Per cent survival, larval period and weight, pupal duration and weight, emergence, adult longevity and fecundity of Heliothis armigera (Hubner) were affected by the pulse species on which it was reared. The pulses could be classified into two groups i.e. pigeon pea and chick pea which were suitable for growth, development and fecundity and black gram, sweet pea, green gram, broad bean and lentil which were unsuitable.

Conessine, the steroidal alkaloid of Holarrhena antidysenterica Wall, possesses a wide range of activities against four insect species viz. Aedes aegypti, Dysdercus koenigii, Spodoptera litura and Pieris brassicae. In D. koenigii the compound inhibits the egg hatching of treated adults and nymphs. In Ae. aegypti the larval developmental periods are extended, resulting in a high mortality rate. Such effects are produced at very low dosages of 0.5 to lOppm. Antifeedant activity is observed against larvae of S. litura and P. brassicae at concentrations of 0.005 to 0.2 % of conessine.

The pink mealybug Maconellicoccus (=Phenacoccus) hirsutus (Green) (Pseudococcidae: Hemiptera) occurs in more than 13 countries, but has a major pest status only in Egypt and India. Its biology, host range, ant association, natural enemies and methods of control are reviewed here.

The colony foundation and development, and pattern of young and established nests of Odontotermes obesus and O. wallonensis were investigated. Swarming of alates of both the species occurred during pre-monsoon (April/May) and continued throughout the wet months. After pairing, alates of both the species selected sites in crevices of the soil or in loose soil for the foundation of a colony. The active construction of the mound was observed during the cool hours of the day in rainy months.

The young nests of O. obesus was conical-shaped with one or more conical turrets, whereas it was dome-shaped with one or two domes like turrets in O. wallonensis. In young colonies, the fungus combs were aggregated in the central cavity and the royal chamber was situated beneath usually at the centre. The established nests of both the species were extended by addition of vaults, galleries, runways, etc. The mound nest was extended in vertical direction in O. obesus, whereas it was extended horizontally in O. wallonensis.

The seasonal changes in water content and fat content of olive psylla, Euphyllura olivina in the field were investigated in two successive years. The overwintering adults of olive psylla had more fat than spring and summer generation adults. There was a steady increase in % fat contents of females from mid-October to early January. The % fat of both sexes decreased sharply in May, June and July. There was a gradual reduction in % water content from mid-June to early October and then decreased steadily until early November. The % water in the overwintering adults ranged from 57.5 to 45% and became constant around 52.5% of live body weight in February and March. Seasonal changes in % water was positively related to population changes of olive psylla. The % water in olive psylla was negatively related to the fat content.

The temporal evolution of the populations of Megalurothrips (=Taeniothrips) sjostedti (Trybom) (Thysanoptera, Thripidae) (larvae and adults) and of Maruca testulalis (Geyer) (Lepidoptera, Pyralidae) (larvae) as well as the rate of flower infestation by these insects was carried out under Held conditions using 10 cowpea varieties (IT 82D-889, IT 82D-287, IT 82D-716, IT 82D-789, IT 82D-703, IT 82D-713, IT 82D-890, IT 82D-709, TVu 57 and “Kpodjiguegue”).

The investigation was carried out during the 1984 early cropping season (from April to July) at Abomey-Calavi. In the research station the abundance of M. sjostedti populations was observed 47 days after planting (DAP) for one variety and 68 DAP for the nine other varieties (384–634 thrips/20 flowers according to the varieties). In addition, the decline of the insect population was recorded 40 DAP for four varieties and 75 DAP for the six other varieties (88–375 thrips per 20 flowers according to the varieties). But 90–100% of the sampled flowers were infested by M. sjostedti towards 40 DAP whereas 95–100% of flowers were injured 68 DAP.

Larval populations of M. testulalis reached their maximum value 40 DAP for four varieties and 47 DAP for the six other varieties (4–17 larvae/20 flowers according to the varieties). The population declined 61 DAP for two varieties, 68 DAP for seven varieties and 75 DAP for one variety (0–3 larvae/20 flowers according to the varieties). Regarding the rate of flower infestation by M. testulalis, the highest percentages (20–70% according to the varieties) were obtained among all varieties from the same sampling dates where the larval population peak was noted for the same varieties. In the same way, lowest percentages (0–15% according to the varieties) were recorded among all varieties on the same dates where the minimum value of larval populations of the pest was obtained.

M. sjostedti and M. testulalis fluctuate in opposed phase. The peak value of M. sjostedti generally coincides with the minimum value of M. testulalis and inversely. But the peak activity period of both insects occurs between 40 and 70 DAP. The average number of insects recorded all along the sampling period has shown significant differences (P=0.05) between the various cowpea varieties for M. sjostedti and M. testulalis. The biological and nutritional factors that contribute to such population fluctuations are discussed in the light of results obtained.

Eurystylus marginatus Odhiambo (Hemiptera: Miridae) was the most important and abundant insect pest of sorghum panicles in Niger in 1985 and 1986. First generation adults initially infested sorghum panicles in late August, and two succeeding generations developed on sorghum. Economic losses were manifested in yield and grain quality reduction. A commonly grown indigenous variety Mota Galmi, suffered 14% yield loss and 19% grain vitrosity reduction in field trials in which E. marginatus density averaged 80/panicle. Among 14 other sorghum varieties grown under natural conditions, vitrosity was decreased 20% on average (range 0–47%). Headcage experiments using 20 female/male pairs of E. marginatus on each of three varieties resulted in losses ranging from 19–62% of grain weight/panicle, 1000-kernel weight, per cent low density grain, and vitrosity. Damage resulted from both oviposition and feeding. Among seven panicle and glume characteristics, percentage coverage of grain surface by glumes, and the time from anthesis to opening of the glumes were significantly correlated with reduced head bug numbers. Among varieties, grain damage was not highly correlated with head bug numbers; but within varieties, increasing head bug numbersclearly caused increased damage. Measureable damage occurred with as few as five female/male head bug pairs per panicle. MostE. marginatus eggs were oviposited into exposed, apical portions of sorghum grains during the milky stage of kernel development. Grain of variety CE90 were vulnerable to oviposition for less than 1 week after glumes opened.

Fourteen differential rice cultivare under four major donor groups were evaluated at 11 field locations in seven Indian states during 13 years against the rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera:Cecidomyiidae). Three basic variations, which qualify to be called biotypes 1,2 and 3 could be identified based on overall reaction patterns against Eswarakora and Siam 29 differential groups. Biotype I cannot damage entries involving either Eswarakora or Siam 29. Biotype 2 is capable of damaging the group of Eswarakora and its derivatives but not able to damage the group of Siam 29. Biotype 3 can damage the Siam 29 group while being incapable of doing so with Eswarakora group.

A survey carried out over Western Kenya in order to determine the prevalence of microorganisms in cereal stem borers and legume pod borer showed the presence of a large number of insect pathogens in the dead larvae. Larval cadavers were recovered from all sampling sites. Bacterial and fungal microorganisms were highly prevalent. Other major groups of microorganisms were also recovered, although at a low level. Viruses (polyhedral inclusion bodies and granulosis viruses) occurred at 2.7% at the Mbita Point Field Station, and 1.1% in the field. Mermithids and rhabditids occurred at 0.4% in the station and 0.6% in the field, whereas the protozoans (microsporidia and gregarines) were more prevalent in the station than in the farmers' fields (9.4 and 1%, respectively).

The spotted stalk borer, Chilo partellus was the most common borer sampled, but Busseola fusca and legume pod borer, Maruca testulalis were sampled in most sites too. Sesamia calamistis and EIdana saccharina were recorded at a low level, and C. orichalcoceliellus was recorded only at the Kenya coast.

Eight potato cultivars namely Anett, Desiree, Feldeslohn, Kerr's Pink, Kenya Baraka, Roslin Eburu, Roslin Gucha and Roslin Tana were tested in the greenhouse to compare their susceptibility to Myzus persicae Sulzer. Differences in the susceptibility of the potato cultivars to aphids were reflected in the number of the apterae aphids that developed on them. Anett, Kerr's Pink and Feldeslohn supported the highest, and Roslin Tana the lowest population of M. persicae. Roslin Tana was found to be resistant. The bottom leaves of most potato cultivars maintained the highest aphid population while the upper leaves maintained the lowest. There were no significant correlations between leaf area and yield of potatoes with the number of apterae aphids on the eight potato cultivars.

EAG recordings revealed that from the six substances isolated so far from pheromone glands of Marnestra brassicae females, only (Z)-11-hexadecenyl acetate (Z11-16Ac), (Z)-9-hexadecenyl acetate (Z9-16Ac) and (Z)-11-heptadecenyl acetate (Z11-17Ac) are perceived by the males. This suggests that these substances may be female sex pheromone components.

The male olfactory sensilla also respond to (Z)-9-tetradecenyl acetate (Z9-14Ac) and (Z)-11-hexadecenol (Z11-160H), which are sex attractant constituents of various closely related species, but act as strong attractant inhibitors on M. brassicae males. This sensitivity to Z9-14Ac and Z11-160H is suggested to enhance the males' possibility to discriminate between conspecific and non-conspecific females.

Single sensillum recordings revealed that in 90% of the male antennal sensilla trichodea tested, three cell types (Types A, B, and C) were active. In the remaining 10% only B and C action potentials were seen. The Type C cells are exclusively responsive to the major pheromone component Z11-16Ac. The Type C cells are activated by the attractant inhibitors Z9-14Ac and Z11-160H, and to a small extent by Z11-16Ac. Responses to mixtures of these substances revealed that addition of Z9-14Ac and Z11-160H to Z11-16Ac changed the activity of the A cells only and did not affect the activities of the A and C cells. It is concluded that volatiles which exclusively or predominantly activate the Type B cells induce avoidance behaviour in the males, whereas substances activating the Type C cells evoke sexual behaviour and are attractive. This offers possibilities for relatively rapid electrophysiological determination of substances inducing sexual or avoidance behaviour. The function of the A cells is not yet clear. These cells respond to low concentrations of Z11-16Ac and Z11-160H, which may enhance the males' capacity to distinguish conspecific from non-conspecific females at a distance, when concentrations are low and the C and B cell activities are small.

It is suggested that cells sensitive to Z9-16Ac and Z11-17Ac are present in a limited number of sensilla only.

The present article is one of a series of papers in preparation in which an ecological approach to developing a sound biocontrol programme for cereal stem borers is proposed and outlined. The proposed approach involves detailed population estimation and analysis in relation to crop phenology to determine the role of local natural enemies, evaluation of biocontrol potential of promising biocontrol agents, developing mass rearing and release technology and monitoring the impact of the biocontrol programme. In the example used to illustrate the first step in such a programme, life table analysis of data from a 2-year study on Chilo partellus on maize and sorghum under subsistence agriculture in Western Kenya, showed local predators (and unidentified factors) to contribute up to 97.6 % of generation mortality of the borer in the age interval from egg to early instar larva, while parasitoids and pathogens contributed less than 1 % mortality in the various life stages. Hence, a programme involving conservation and augmentation of local predators and introduction of selected exotic parasitoids of this borer seems appropriate. This represents an attempt to apply life table analysis, taking into account plant phenology, in studying interacting populations under subsistence farming conditions.