The present study revealed that the ratio of antennal to body length in Lipaphis erysimi (Kalt.) increased from 0.55: 1.00 in the first instar to 0.75: 1.00 in the adult alatae as compared to apterae, where the ratio stayed almost the same. The antenna showed specific growth regions i.e. first and fourth annuli, where the increase in size was more compared to other parts. Five morphologically distinct types of sensilla were recorded i.e. sensilla companiform. sensilla trichodea with enlarged spatulate tips, sensilla trichodea with tapering uniporous tips, plate organs and coeloconic pegs. The distribution pattern of these sensilla showed that the number of sensilla trichodea increased during the development, the increase was more in alatae compared to apterae. The secondary sensoria were restricted to adult alatae only, but could be seen under the cuticle in fourth instar alatae. In addition, the variation in the surface sculpturing in the form of scale-like projections were also observed on the antenna.

Antixenotic and antibiotic components of resistance to the cassava mealybug, Phenacoccus manihoti Matt. Ferr. were evaluated in different varieties of cassava (Manihot esculenta Crantz), in Poinsettia (Euphorbia pulcherrima Wild), Talinum (Talinum triangulare Jack) and Faux-caoutchouc (hybrid of M. esculenta and M. glaziovii Mull. Arg.). Resistance, was estimated in the field on 25 varieties of cassava by means of varietal screening. Although we were unable to identify varieties ofcassava totally resistant to P. manihoti, there was evidence of partial resistances. Thus the Incoza variety is the most resistant, followed by the Moudouma and Zanaga varieties. On the other hand we found very susceptible varieties, such as Dikonda, Kataoli, 3M8 and 1M20. Laboratory evaluations of the antibiotic component of resistance, made by estimating the intrinsic capacity for increase rc, showed that the host-plantshave a considerable effect on the multiplying capacity of the mealybug. Indeed rc ranges from 0.038 (Poinsettia) to 0.160 (Ganfo cassava variety), i.e. a ratio of 1 to 4 between the two extreme values. If the cassava varieties alone are considered, the percentage of maximum variation is 20% between the Incoza (rc = 0.133) and Ganfo (rc = 0.160) varieties. The Incoza cassava variety is the most resistant, in terms of both antixenosis and antibiosis. Classification of the other cassava varieties, from the most to the least resistant, differs according to the resistant component under consideration. Poinsettia and Talinum both have a very strong antixenotic component, but their antibiotic component differs (rc = 0.038 and 0.150 respectively). Our results suggest that the resistance mechanisms of the host-plants of P. manihoti intervening in the fixation of the pest (antixenosis), are different from those acting on the development of the mealybug (antibiosis). We established significant correlations between the size of the mealybugs and their demographic characteristics for all the plants studied: the duration of the prereproductive period is shorter and the net reproduction rate is higher when the mealybugs are large-sized. These results are discussed in the context of an integrated monitoring programme.

Malathion tolerance of the rose-grain aphid Metopolophium dirhodum (Walker) reared on the ancient wheat variety Emmer (Triticum dicoccum L.) was tested by topical bioassay and found to be lower than that of aphids reared on the modern more susceptible variety Marts Kinsman (T. aestivum L.). On both varieties, tolerance was greater at stem elongation than at the tillering stage of plant growth. All statistically significant differences when plants were treated with Cycocel and MCPA showed that the two chemicals, respectively, reduced and increased aphid tolerance to malathion, in keeping with the effects of the chemicals on induced plant resistance to aphids reported in the literature. Probit mortality slopes were not progressively altered by changes in LC50, so that similar differences in aphid tolerance to malathion were found at both LC59 and LC90 levels.

The distribution of 31 Glossina spp. and subspecies belonging to fusca, palpalis and morsitans groups is given for 38 African countries. The natural hosts of 17 tsetse species and subspecies from many areas within different regions of Africa are also given. These were collated from the results of both published and unpublished work, for the period 1953 to 1991 inclusive, comprising altogether 47, 697 bloodmeals. This review is aimed to provide current knowledge on the distribution as well as the natural hosts of tsetse.

A tsetse survey was conducted around the Lambwe Valley in South West Kenya in order to establish the extent of Glossina pallidipes distribution outside the Valley. Between October 1988 and March 1989 flies were found far outside the Lambwe Valley. A proportion of these flies was infected with three species of trypanosomes. The capture of teneral flies suggested that breeding was occurring and that viable populations of G. pallidipes therefore exist away from the core breeding areas in the valley.

Among the eight entomopathogenic fungi tested against the termite, Odontotermes obesus (Rambur), five fungal pathogens viz., Beauveria bassiana (Bals.) Yuil, Metarhizium anisopliae (Metsch.) Sorokin var. anisopliae, M. flavoviride Gams Rozsypal var. minus, Paecilomyces lilacinus (Thom) Samson and P. fumosoroseus (Wize) Brown & Smith, were pathogenic. Three other fungal pathogens viz. Verticillium lecanii Zimm, Paecilomyces farinosus (Holm, ex Gray) and Nomuraea rileyi (Farlow) were not pathogenic. B. bassiana was the most effective pathogen against termites, followed by M. anisopliae, M. flavoviride, P. lilacinus and P. fumosoroseus. Workers minor, of the three morphogenetic forms of O. obesus, were the most susceptible, followed by workers major and soldier caste. Bioassay on isolates of two most virulent termite pathogens, B. bassiana and M. anisopliae revealed that B. bassiana isolate Bapatla was the most effective fungal pathogen with the lowest LC50 (9.98 × 104 conidia/ml)

The lowest weight at which a final instar larva of the leafroller, Cnephasia jactalana (Walker) (Lepidoptera: Tortricidae) can initiate pupation, the larval critical weight, was unaffected by diet quality. Use of a non-nutritive artificial diet showed that the larval-pupal metamorphosis was possibly triggered by stretch receptors, and was not related to nutrition per se. However, a final-instar larva was not able to moult until it had ingested and assimilated the quantity of food required to attain the larval critical weight. The period between attaining the larval critical weight and the larval maximum weight is the latent feeding period which was found to be longer on higher-quality diets. The decrease from larval maximum weight to pupal weight depended on diet quality: optimum-quality diets gave the smallest decreases. The decrease from pupal to adult weight was not affected by diet. Reproductive performance was strongly affected by the quality of the diet during the latent feeding period.

A study of the noxiousness of the African white rice stem borer, Maliarpha separatella Rag carried out under controlled field conditions has revealed that the impact of this pest on the yield and its components is assessable. For mean infestation rates up to 68% during the period of highest sensitivity of a paddy rice culture (second half of tillering to panicle initiation), no significant decrease could be observed in the number of panicles, nor any significant increase in the number of white heads and the number of empty grains per hill. However, with increasing infestation rates, the number of immature panicles increased and the number and weight of filled grains per hill decreased. An explorative analysis of the infestation rate-yield loss relationship, showed that a sigmoid model describes this interdependence appropriately. The proposed economic injury level (EIL), is here considered more the result of an approach, which had as its goal the re-definition of the status of the pest than as an instrument of a chemical control programme with treatments based on an action threshold.

Aqueous extracts (5%) of the seeds Parkia clappertoniana (Jacq), Azadirachta indica A. Juss, and Piper guineense Schum and Thonn caused 90% mortalityof the worker caste with P. guineense, and 86% mortality with A. indica and P. clappertoniana respectively within 3 hr of topical application. At 24 hr, mortality of Macrotermes nigeriensis (Sjostedti) workers was 100% with the same concentration of each extract. Oral toxicity at 3 hr to the worker caste using cuttings of cassava, Manihotesculenta Crantz impregnated with each extract gave 65% mortality with Piper, and 45 and 29% with Azadirachta and Parkia, respectively. Mortalityby oral toxicity reached 100% in 12 hr with Piper, 95 and 69%, respectively with Azadirachta and Parkia. Increasing the concentrations of each extract to 15% did not significantly (P > 0.05) increase the toxicities of the extracts to the worker caste even at prolonged exposure periods.

Nature of resistance against the rice leaffolder, Cnaphalocrocis medinalis (Guenee) was studied in 16 rke varieties selected on the basis of greenhouse feeding test. Resistant varieties as a group were less preferred for feeding by the larvae in a free choice test lasting 10 days. Cut leaf assay with limited choice brought out subtle differences among some of the test varieties In larval settling response. Larval preference was correlated positively with the leaf area damage noted In feeding test, per cent pupation and leaf width, and negatively with trichome density. However, oviposltton preference was neither distinct nor correlated with resistance or leaf morphology. An antibiosis component in the test varieties ARC 11128, Balam, Gorsa, ARC 7064 and Ptb 19 was distinctly manifested as reduced larval survival, lower pupation rate and pupal weights in comparison with the susceptible check. When neonate larvae were reared on the meridic diets containing the leaves of the varieties Darukasail, Balam or Ptb 12, antibiotic effects were much more pronounced in comparison with the larvae reared on the diet containing the leaves of the susceptible check TN 1.

The biology of Maruca lestulatis Geyer was studied on different parts of 18 cowpea cultivars to determine the role of antibiosis in their levels of resistance. M. testulalis larvae were successfully reared from first instar to adult stage on floral buds, flowers and sliced pods, but not on stems, terminal shoots and intact (unsliced) pods, where there was complete larval mortality. The mean pupal weight ranged from 43.5–54.5 mg on floral buds, 38.5–58.6 mg on flowers and 42.7–58.6 mg on sliced pods, with highly significant differences between (P ≺ 0.01) resistant and susceptible cultivars on each part. Growth indices showed that sliced pods were the most suitable for larval growth and development, followed by flowers and floral buds.

The levels of resistance found were inadequate for solving the M. testulalis problem in cowpea. Selection and breeding for cowpea ideotypes (architypes), to combine such resistance with morphological, biochemical and biophysical traits, could enhance the low levels of resistance in the cowpea crop and ultimately lead to the effective management of this pest. The correlations between growth and development parameters showed that larval period had the most influence on M, testulalis survival and population build-up in the succeeding generations.

Five-to six-day old male pupae of Ectomyelois ceratoniae Zeller were irradiated with 0, 20, 25 and 30 krad of gamma rays. When the radiated males were mated with normal females there were deleterious effects on fertility without extreme effects on mating or fecundity. Percentage of embryonated eggs and progeny per female decreased to two thirds of the control by 25 and 30 krad treatments. Productivity of the female mated with irradiated males was decreased and significant reductions in egg viability, egg hatch and larvae per female were observed in F1 generation. Similar pattern of sterility was observed in sibling crosses of F2 at the three doses.

A volatile female sex pheromone, secreted by the pygidial glands of Blattlla germaniea, which attracts males from a distance was studied. Ultrastructural studies showed common epidermal and canal cells associated with glandular cells, classified as class 3 secretory unit The thickness of pygidial glands from young virgin females Increased progressively and became larger, 10 to 13 days after adult emergence. It decreased markedly after mating and increased again after the release of the ootheca. Based on the morphology of the glands, it was further observed that B. germaniea young virgin females' attractiveness increased gradually, such attractiveness decreased at mating. After larval emergence, females' attractiveness wasonce more enhanced. Dkhktromethane extracts of pygidial glands attracted males from a distance. These results demonstrate the pheromone gradual secretion and similarly pygidial glands evolution during adult emergence.

An additive effect was obtained after treatment of Spodoptera littoralis (Boisd.) larvae with a combination of Bacillus thuringiensis and nuclear polyhedrosis virus (NPVs). The NPVs was the more pathogenic followed by B. t., cytopathologically. Simultaneous application of B. t. and NPVs affected the midgut cells by causing a very specific appearance of cell hypertrophy with some deposits of B. t. crystals on the fourth day of infection as shown by scanning electron microscopy. Transmission electron microscopy showed that the vegetative cells and spores of B. t. entered the midgut epithelial cells followed by the virus. It is possible that the initial destruction caused by the B. t. toxin facilitated penetration and entry of the virus.

Rhipicephalus appendiculatus salivary glands extracts and saliva contain both biochemically active and pharmacological agents with various effector functions, including inhibition of host enzymes or inactivation of other host molecules that may be important in mounting tick rejection. The majority of these salivary biochemicals may interact with host antibodies at the feeding site or in the gut (or both), that interfere with proper tick attachment and feeding. The possible role of these biochemicals in tick feeding is discussed. Of particular interest is a salivary anticoagulant, which increased as feeding phase progressed and was present in all life cycle stages of the tick. Antibodies raised in rabbits against salivary gland extracts obtained from female if. appendiculatus fed on rabbits for various days, recognized several antigens on Western blots of salivary gland extracts, but failed to react with the purified tick salivary anticoagulant molecule. Thus, tick anticoagulant was poorly immunogenic compared to other salivary moieties. These results may help to explain the strategies adopted by the tick to circumvent biochemical detachment by the damaging host-protective immune responses, thereby enabling the vector to co-exist with its mammalian hosts.

Sesamia calamistis Hampson and Eldana saccharina Walker larvae were reared at 25°C on pieces of stem from five indigenous African grasses. All five, Andropogon sp., Panicum maximum Jacq., Pennisetum polystachion (L.) Schult., P. purpureum L. and Sorghum arundinaceum (Desv.) Stapf. have been reported as host plants for one or both species. Larval survival, larval and pupal period and pupal weight were recorded and compared to values of these parameters for larvae reared on stems of maize and on artificial diet. S. calamistis larval survival was less than 10% on each grass species compared to 95% on artificial diet and 30% on maize stems. Larval period was similar on maize and the grasses, but was 50% faster on artificial diet. Pupal periods were similar for larvae reared on grasses, maize and artificial diet. Pupal weights were highest for larvae reared on artificial diet, followed by maize and then grasses. E. saccharina larval survival was less than 5% on each grass species compared to 60% on artificial diet and 19% on maize stem. Larval development was 25% faster on artificial diet than on maize or grasses. Larvae reared on grasses, maize and artificial diet had similar pupal periods. Pupal weights were lowest on grasses and highest on artificial diet.

The occurrence of an orange body coloured mutant, governed by a single somatic recessive gene of the cotton stainer, Dysdercus koenigii is reported. Both the strains did not show any quantitative difference in growth, development and reproductive biology. Males of the orange mutant lacked any special preference for females of orange mutant. Inheritance of the orange mutant in mixed population showed its relative stability at about 21% from F2 to F8 generations. The utility of the orange mutant for studies on population genetics and dynamics of the cotton stainer is discussed.

Greenbug, Schizaphis graminum (Rondani), an important vector of barley yellow dwarf mosaic virus, is a major pest of cereals in many countries. A preliminary survey conducted in the Punjab and North Western Frontier Province of Pakistan revealed medium to heavy infestations at Charsadda (density 12 apterous greenbugs/25 plants), Sher Shah (Multan) (density 33) and Malkot (Murree) (density 114). However, it was found in small numbers at many other locations.

A culture of greenbugs collected from Charsadda, was established on susceptible wheat cultivar Faisalabad-83 at 27 ± 3°C, 60% r.h. and 16:8 hr day:night regime. A seedling bulk test using local and exotic host differentials indicated that DS-28A and Largo wheat were susceptible, whereas Amigo wheat, Post and Will barley were resistant. This indicates that the population of greenbug from Charsadda culture was different from greenbug biotypes occurring in the USA. Therefore, it was designated as biotype PK-I for future reference.

Of the 44 recommended wheat cultivars in Pakistan, Punjab-85 was found to be resistant (visual damage rating (DR) 3 at 0 to 9 damage scale; 0, healthy; 9, dead). Faisalabad-85 had a DR of 4, PARI-73, Sandal and Yecora had a DR of 5, and PAK-81, WL-711, Sutluj-86 and Nuri-70 had a DR of 6. All the remaining cultivars were highly susceptible to greenbug (DR ≻ 6).

Three tests, namely, antixenosis (non-preference), antibiosis and tolerance, were conducted to determine the nature of resistance in selected entries. In the antixenosis test, PARI-73, WL-711 and Yecora were found to be the least preferred. The lowest fecundity (antibiosis) of the greenbug was on Punjab-85. In the tolerance test, the lowest damage was recorded on PARI-73 (DR= 4.1), followed by Sandal (DR= 4.8) and Punjab-85 (DR= 4.8). These three tests indicated that resistance in Punjab-85 is mainly due to antibiosis and a low level of tolerance.

During this study 439 native wheat germplasm lines were also tested. Of these, 16 germplasm lines (PAK 15081, PAK 15115, PAK 15139, PAK 15242, PAK 15433, PAK 15479, PAK 15481, PAK 15519, PAK 15992, PAK 15994, PAK 15995, PAK 15997, PAK 16007, PAK 16008, PAK 16010 and PAK 16190) were found to have a high level of resistance (DR ≺ 3). Of the test entries, 114 were moderately resistant (DR= 4–6) and the remainder were susceptible (DR ≻ 6) to greenbug. The germplasm lines found resistant may have different genes for resistance which can be exploited in breeding programmes.