Viruses have been identified in a large number of insect species and many have been shown to have a regulating effect on natural populations of insects. Increasing dissatisfaction with the use of chemical pesticides has resulted in a search for biological control agents such as viruses. A number of insect viruses, primarily the occluded viruses (baculoviruses and cytoplasmic polyhedrosis viruses) have been used effectively to control pest species of insects. This review describes the major groups of viruses which infect insects and the areas of research that are being pursued.

Glossina pallidipes was recorded from two widely separated areas in southern Sudan, far from any previously known localities: west of Torit, Eastern Equatoria Province and around Yambio, Western Equatoria Province. These records are discussed in relation to the local habitat and associated tsetse species; and it is suggested that G. pallidipes may be becoming more common and widespread in the region.

Three populations of C. mbila originating from the rain forest (Ibadan), southern part of sudan savanna (Kadawa, Kano) and the Jos Plateau, and C. triangula population from Ibadan (Moor Plantation) were compared in relation to their ability to acquire and transmit maize streak virus (MSV). Acquisition and transmission efficiency increased with time of access feeding. Joint regression analysis showed that the populations did not differ significantly from each other in transmission efficiency of the virus. Nymphs and adults of some populations acquired MSV in 30 sec and adults transmitted the virus during the 2-hr inoculation access. Efficiency of virus transmission generally increased with acquisition or inoculation time.

The minimum latent period of maize streak virus in the various Cicadulina populations was 14–18 hr and the medium latent period (LP 50) was 16–20hr. Some individuals in all populations retain the virus throughout their lives.

Since the various Cicadulina populations were largely similar in their ability to acquire and transmit the virus into healthy maize, other factors which might be implicated in the epidemiology of maize streak disease are discussed.

Floral fragrance oils related to pollination were studied in three species of Theobroma and one Herrania species (Sterculiaceae) in Costa Rica. This study was prompted by field observations that floral odours and floral visitors are markedly different between Theobroma and Herrania, as well as between species of Theobroma.

Floral fragrance in cultivated T. cacao consisted of 78 components, primarily saturated and unsaturated hydrocarbons, with 1-pentadecene the major constituent followed by n−pentadecane. The distribution of 1-pentadecene was similar at 0900 hr (43.6%), 1130 hr (52.5%) and 2000 hr (51.1%) sampling times but only 1.2% at 1600 hr. The ratio of 1-pentadecene to n−pentadecane in the 1600 hr sample, approximately 1:6, contrasted with a 3:1 ratio at 0900 and 1130 and a 6:1 ratio at 2000 hr. The greatest concentration of volatiles was found in the 1130 hr sample, with 0900 and 2000 hr concentrations being essentially equal and intermediate between the high (1130 hr) and the low (1600 hr).

Of the 58 compounds detected in T. mammosum steam distillate at 0815 hr, an array of linalool oxides accounted for 12.5% of the oil followed by isoeugenol (8.9%). Saturated hydrocarbons were also present but, unlike T. cacao, n-tricosane was the major hydrocarbon (12.2%). The major constituents of T. mammosum oil clearly distinguish this species from T. cacao.

A markedly different profile of major floral volatiles was found in T. simiarum: major constituents included the monoterpenoids citral, geraniol, nerol, and citronellol. Unlike the oily, hydrocarbon fragrance of T. cacao and T. mammosum, T. simiarum floral fragrance is citrus-like both in the field and laboratory. Our fragrance studies suggest considerable evolutionary divergence within Theobroma.

The floral fragrance of H. cuatrecasana contained volatiles characteristic of dipteran-pollinated plant species. Unusual volatiles found in Herrania fragrance included iridomyrmecin, guaiol, and other azulenic derivatives. No such monoterpenoids and bicyclic sesquiterpenoids (with the exception of longifolene, 0.1%, in T. simiarum) were found in Theobroma. The profiles of floral fragrance chemotaxonomically support the exclusion of Herrania spp. from the genus Theobroma.

Egg-masses of Simulium damnosum s.l. were investigated to explain the frequent presence of undeveloped eggs in the lower layers. Natural development within egg-masses depended on whether eggs were laid (a) all at once or (b) were added to on consecutive evenings. In the field where the development of eggs from situation (a) was followed, top layer (TL) eggs hatched in 2 days when unexposed bottom layer (BL) eggs were still white. BL eggs uncovered 12 hr after oviposition were undeveloped, then hatched in 3 days. BL (a) eggs uncovered after 5 days were still untanned and undeveloped but were not further investigated.

In the laboratory, portions of egg-masses—intact or with the BLs exposed—were incubated in Petri dishes with and without preceding KOH egg separation treatment, or in flowing water. Other samples of BL eggs were incubated at different O2 levels. In Petri dishes, most TL eggs hatched within 24 hr of setting up but exposed BL eggs hatched (if at all) after much delay in 6–14 days. No unexposed BL eggs hatched even after TLs above them had done so. Transfer to flowing water or KOH treatment increased hatching and reduced the delay. Hatch rates of exposed BL eggs rose from 2.7 to 63% with increased O2 levels.

Implications with regard to laboratory culture and control operations are discussed. Mortality of covered eggs could be a potent population regulating factor within and perhaps even between species of the S. damnosum complex.

Laboratory studies were carried out to determine factors which induce larval diapause in a Nigerian strain of Plodia interpunctella.

Larvae reared at constant temperatures of 20 or 30°C did not enter diapause. However, 13.3 and 37.7% respectively of larvae reared for 8 or 12 days (third or fourth instars) at 30°C and then transferred to 20°C entered diapause. Larvae transferred to 20°C immediately after hatch (first instar) and after 16 days (final instar) did not enter diapause. Developmental periods from egg-hatch to adult of diapausing individuals ranged from 136 to 151 days, while those of non-diapausing individuals reared at constant temperatures of 30 and 20°C ranged from 23 to 34 days and 60 to 72 days, respectively.

Different photoperiods did not induce diapause when reared at constant temperatures but exposure of larvae that experienced a drop in temperature from 30 to 20°C, at 4th instar stage to continuous light or to a long photoperiod (light 16 hr: dark 8 hr) caused a drop in the percentage larvae that diapaused.

Larvae reared at high larval density at 30°C did not enter diapause, and increased mortality was observed.

Fly catching experiments using the biconical trap and a vector collector (under mosquito net) were performed in different biotopes of the forest zone in Côte d'Ivoire (Daloa region).

Of the three species of tsetse usually caught, Glossina palpalis, and to a very minor degree Glossina pallicera, was attracted to man. G. palpalis showed vis-a-vis man a clear difference in attractiveness according to the point of capture. In those habitats where hosts were rare and dispersed (gallery forest, coffee and cocoa plantations) this species frequently attacked man who came into contact with it during the accomplishment of his usual activities, whereas in the village it voluntarily abandoned him in preference for pigs. Whatever the type of biotope, the trap had the same attractiveness. Its use, in contrast to captures on man, enabled a simultaneous study of diverse species that co-existed anthropophilically or zoophilically.

Although almost all the tsetse taken in the trap or on vector collector were hungry, it was noticed that the number of females in the trap samples was always higher than that of males.

The susceptibility of the different stages of Sitotroga cerealella (Olivier) to gamma radiation was studied. The stages arranged in a descending order according to the values of gamma radiation LD50 are: adults (190.100 krad) for females and 183.200 krad for males, pupae (6.039 krad), 3 days old eggs (5.570 krad), one week old larvae (4.800 krad), 1-day-old eggs (4.181 krad) and 2 weeks old larvae (3.056 krad).

The plant factors that contribute to the abundance of beetles in coffee fields were studied and analysed relative to shoot and canopy features of the host plant. During infestation Dirphya nigricornis Olivier constructed niches within specific heights (145.0–210.0 cm) of the canopies such that there was a highly significant (r = 0.99, P = 0.001) availability of adequate habitat for larval development. The adaptation of the pest to the host plant was good, irrespective of varieties and culture systems of the coffee plant. It was concluded that the alignment of eggs to tip internodes synchronised the newly hatched larvae with the coffee tissues, usually between 0.5 to 30 cm off the shoots, of extremely low dry matter, and high moisture content, such factors favouring early larval development.

The horseflies in a patch of gallery-forest in a savannah of French Guiana were collected by 1°) for 24 hr with a Malaise trap, and 2° for 2 hr at dawn and at dusk, with a Malaise trap baited with carbon dioxide. The crepuscular horseflies, Cryptotylus unicolor, Chlorotabanus mexicanus and Chlorotabanus inanis, were more abundant in the baited trap (average: 55% of the flies collected) than in the unbaited trap (3%). Seasonal changes in relative abundance of the crepuscular species were evident in the baited trap only. The baited trap caught more flies and more species (averages: 315 flies and 7.5 species per 2hr catch) than the unbaited trap (averages 64 flies and 5.1 species per 24 hr catch). However, the overall number of species collected in each trap during the study did not differ greatly (16 species for 126 catches of 24 hr for the unbaited trap vs. 14 species for 29 catches of 2 hr for the baited trap).

The study showed how trails were established with and without any food source. The two stimulants for strong trail-laying by the termites were found to be: (1) a virgin (trail-less) surface, and (2) a discovered food source. Whenever a food source was discovered, the returning workers (from the food source to the nest) increased strong trail-laying (STL) activity more than the outgoing termites.

The results also confirmed that there was no trail specificity (neither in artificial trail extracts nor in natural trails) between different colonies of Amitermes evuncifer. This means that in trail bioassays, test termites can be taken from any colony (of the same species). A method devised for extracting, preserving as well as carrying out tests with extracted natural trail was discussed.

Trail activity was measured in terms of “trail unit” (TU). The trail activity of a single worker sternal gland was found to be 15,000 TU. This is the highest activity ever found in a worker of any termite species. This study has confirmed chemical communication in Amitermes evuncifer.

Temperature influences the reproductive capacity of the Saissetia coffeae and its parasitoid. The lowering of temperatures increased the egg production of the scales. The high temperature (30°C) reduced the egg-laying of Metaphycus helvolus and resulted in a greater proportion of male progenies. However, oviposition and sex ratio of Scutellista cyanea were unaffected by high temperature. The high temperature too, accelerated the development of ovarian eggs of both parasitoids.

Growth and reproduction in Heliothis armigera is known to be controlled by temperature, relative humidity and host plants. Photoperiod was also found to be an important extrinsic factor regulating the different biological aspects of H. armigera. The effect of five alternating light and dark cycles on the adult as well as on the immature stages of this pest was studied at 25 ± 2°C.

The results obtained showed that the photoperiod regimes tested on the adult stage has a high significant effect on reproduction and longevity. Also 16 hr photoperiod was the most suitable condition for maximum egg deposition and maximum percentage of egg hatching.

The immature photoperiod regimes had a high significant effect on the larval duration, pupal weight and percentage of emergence of adults, but had no effect on the pupal duration. Combined effect of immature and adult photoperiod regimes affected greatly the fecundity and longevity of the adults.

DNA replication in the spermatogonial cells of Schistocerca gregaria and Gryllotalpa fossor has been analysed. This study has demonstrated the presence of at least two discrete populations of spermatogonial cells in both the insects with different intermitotic timings. The replication pattern of the sex chromosome in Schistocerca seems to be dependent on the pycnosity status, whereas, in Gryllotalpa, it is independent of the condensation pattern.

The relative activity of three concentrations of Spodoptera littoralis nuclear polyhedrosis virus (SLNPV) against Ceratitis capitata were determined by (a) submerging two egg age groups, freshly laid eggs (0–2.5 hr) and more older ones (0–24 hr) in viral concentrations, and (b) feeding newly hatched larvae on viral contaminated media. Pupations that resulted from all viral treatments were decreased with increase of virus dose. Hatchability showed the same relation, but hatchability of treated old eggs were not significantly influenced by increases in viral concentration. Adult emergence was significantly reduced due to viral treatments to eggs, however, it was increased in the case of feeding the larvae on contaminated diet. The most hypothetical probability of this deleterious effect may be attributed to an activation of an indigenous virus already present in C. capitata. More research is required to understand the basis for the deleterious effect of SLNPV on the fruit fly.

Four types of trap, yellow water, yellow sticky board, bottle with 20% protein hydrolysate, and funnel with 10% casein hydrolysate, were field-tested to control Liriomyza huidobrensis (Blanchard) in the coastal region of Peru. The yellow sticky boards were the most effective in trap capture with a mean of 1193.92 L. huidobrensis per week. The male:female capture ratio was 16:1.

Five parasitoid species, Halticoptera palellana, Chrysocharis phytomyzae, Chrysocharis sp., Diglyphus sp. and Opius sp., were also trapped. A significant negative correlation (r = −0.607 at P < 0.05) was observed for female leafminer capture vs temperature. Wind velocity was positively correlated with parasitoid capture (r = 0.509 at P < 0.05). The population of adult L. huidobrensis was significantly lower (P < 0.05) in plots with yellow sticky boards. Yields in plots with yellow sticky boards and those treated with insecticides were similar and significantly higher (36%) than check plots.

Field studies on aphid species on cabbage were conducted from 1982 to 1984. Brevicoryne brassicae L. commonly occurred on cabbage in Jos Plateau. No aphids were observed on plants transplanted in November 1982 within the first 2 weeks while those transplanted in January 1984 and February 1983 and 1984 usually had a weekly mean of more than five aphids/plant which necessitated application of aphid control treatment. High uncontrolled infestations of B. brassicae on plants aged 2–3 weeks after transplanting usually resulted in stunted growth, plant death and low yields. Decis at 7.5, 12.5 and 17.5 g a.i./ha, dichlorvos at 500, 750 and 1000 g a.i./ha, carbofuran 3 G at 1000 g a.i./ha, carbaryl 85 at 1000 g a.i./ha, and hand-washing of plants with water were used in the study. Decis, dichlorvos and carbofuran applied at 12.5, 750 and 1000 g a.i./ha respectively, were more effective in B. brassicae control. The overall cumulative mean number of B. brassicae/plant on untreated plants were 1300, 1087, 1672 and 565 for crops one to four respectively. For each crop the mean aphid number on untreated plants was significantly higher (P < 0.05) than those on treated plants. For each of the 1984 crops the yields (kg/head) from treated and untreated plants, did not differ significantly (P > 0.05), but for each of the 1982 and 1983 crops, the yields from treated and untreated plants differed significantly (P < 0.05). Plants receiving the washing technique of aphid control out-yielded untreated plants while carbofuran treated plants generally out-yielded plants receiving all other treatments.

The effect of 10, 20, 30, 40, and 50 adult Sitophilus zeamais on the quality of 1 kg lots of white maize maintained at 25−30°C and 65−85% r.h. was observed. Per cent moisture, oil, Free Fatty Acid (FFA) content and germination were determined at 2-week intervals for 10 weeks.

Moisture content of infested maize ranged from 11.51 to 12.92%. There was a significant correlation between moisture content and degree of infestation (r = 0.88; P < 0.05; Y = 11.908 + 0.006 x). The range of oil content of infested maize was 4.83−5.75%. There was a significant correlation between oil content and degree of infestation (r = −0.097; P < 0.05; Y = 5.08 −0.0076 x). The free fatty acid (FFA) of infested maize was 5.82−6.86%. The heterogeneity at various infestation levels was significant (F = 81.38; d.f. = 5; P < 0.001). There was an increase in FFA, with increasing infestations, although the correlation was not significant.

The germination of maize, 10 days after planting, at various infestation levels was 43.0−97.5%. There was a decrease in germination, as level of infestation increased. The heterogeneity in germination at various infestation levels was significant (F = 19.21; d.f. = 5; P < 0.001). Possible reasons for the results obtained, are presented.