The ability of males of Ephestia cautella to mate and transfer sperms aftergamma radiation as 5–6–day old pupae was investigated. The results indicate that gamma radiation had no significant effect on mating, sperm transfer and percentage of egg hatch.

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.

A bioassay was developed to assess the in vitro feeding responses of Chilo partellus larvae to susceptible (Inbred A) and resistant (MP 704) maize varieties. Consumption of internode tissues from the two maize varieties differed while the reverse was true for the nodes. Aqueous extracts from the two varieties caused a decrease in feeding and weight gain, but these effects were more evident in MP 704 than in Inbred A treatments. This suggests that MP 704 has a water extractable factor affecting weight gain negatively. Dose-response curves of neural responses from the maxillary styloconica sensilla showed that aqueous extracts from the two maize varieties evoked different functional forms of impulse frequencies especially in the lateral sensilla. These observations suggest that the quality of gustatory stimuli in the two maize varieties differs.

The population patterns of eggs, larvae and puparia in the bean plants and leaf punctures made by adults were investigated during cropping (March–July and October–January) and noncropping (July–October) seasons at two sites in Kenya. The beans planted in noncropping seasons had more leaf punctures, eggs, larvae and puparia than beans planted in cropping seasons. Beans planted in noncropping season attracted unusually high population from surrounding weeds as well as previous crop which cause severe damage. Under field conditions Ophiomyia spencerella Greathead and Ophiomyia phaseoli Tryon were the species of bean flies infesting the bean plants in all seasons. Both O. spencerella and O. phaseoli normally oviposited in punctures on the leaves but O. spencerella also oviposited in the stems of bean seedlings.

Antixenosis component of resistance to corn planthopper, Peregrinus maidis (Ashm.) was investigated in 10 selected sorghum genotypes at three plant growth stages (30,45 and 60 DAG) under laboratory and field (rainy and postrainy seasons) conditions. In a free-choice test, the orientationa) and settling responses of nymphs and brachypterous adults on all genotypes although influenced by the olfactory and visual responses, then- feeding was notsustained due to gustatory stimuli indicating their significant role in determining the degreeof antlxenosis. The genotypes IS 18676, IS 19349 and IS 18677 showed a high degree of antixenosls in settling fewer nymphs and adults consistently at 30,45 and 60 DAG. This finding was supported with low colonization of nymphs, and brachypterous and macropterous adults under field conditions. In addition, high degree of antixenosis for oviposition in both laboratory and field tests was evidenced on IS 18676 and IS 19349 at 30,45 and 60 DAG, but on SPV 472 and SPV 475 only at specific plant growth stages. The variability in the rate of adult colonization together with suitability of plant growth stages for oviposition has contributed to variable degrees of antixenosis for oviposition.

Studies on relative susceptibility of 78 citrus varieties/hybrids to the incidence of black citrus aphid, T. aurantii under tropical humid conditions in south India revealed that none of the varieties was completely free from aphid incidence. The varieties Nagpur Mandarin and Ikeda Unshiu among mandarins; Longsport Valencia, Campbell Valencia and Washington Navel among sweet oranges; and Carrizo Citrange a hybrid and Dessert Orange, Eureka Lemon, Grape Fruit Pink and Jatti Khatti, among acid citrus group, recorded significantly least mean number of aphids per flush and can be effectively used in breeding programmes.

Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20–25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants. There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.

Polyphenism is a common feature in the mustard aphid, Lipaphis erysimi (Kalt.) in tropical countries. The function related changes in basic biochemical pool are reported during development of polyphenic forms. A gradual decrease in the protein content in this aphid was recorded, as the nymphs advanced in their instar number and reached adult stage. However, the protein content was significantly lower in the apterous forms as compared to alate. The number, density and mobility of protein bands varied as the nymphs passed through different instars and the number of bands was more in alate forms. The glycogen and trehalose contents showed a decrease upto the third instar and showed an increase in the fourth instar, but again declined in the adults of both the phases.

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.

Blister beetles have recently become the key pests of food crops in Mali and Senegal. The endemic areas of most destructive species, Psalydolytta fusca Oliv., P. vestita Duf., are situated in Northeast Mali and Central South Senegal. Host plants of certain species were identified. Light traps were used to study population dynamics of major species at Béma and Samé (Mali), and at Bambey, Gossas, Sokone and Nioro du rup (Senegal). Abundance of P. fusca and P. vestita populations in September–October generally coincided with sorghum and pearl millet flowering. Number of P. vestita beetles trapped was higher than that of P. fusca.

A ‘rice garden’ with monthly plantings of rice was established in an irrigated lowland area in April 1993 and continued for 3 years. Populations of the most common insects, the stalk-eyed flies, Diopsis spp., and the green leafhoppers, Nephotettix spp., and spiders and stemborer damage varied distinctly in relation to month of transplanting. Arthropod populations also exhibited distinct patterns in relation to crop growth stage. Grain yields varied with month of transplanting but there was no distinct trend from one year to the next. This study indicated that continuous cropping of the same fields over a 3-year period did not result in a build-up of insect pests or a decline in grain yield.

Investigations on the biology of Cinara cupressi, a voracious aphid of cypress trees in Kenya, showed that the aphid produced four nymphal instars within a fortnight under laboratory conditions of 22°C and 89% r.h. Reproduction was two nymphs per female adult per day for 12 days of reproduction. Nymphal multiplication was brisk, but was drastically countered by mortality which was highest in the first, third and fourth instars. This led to a mere nymphal survival of 11.0% at most under laboratory conditions.

Sorghum head bug, Calocoris angustatus Leth. (Hemiptera: Miridae) is an important insect pest of sorghum in the semi-arid tropics. A technique to screen for resistance to head bugs under field conditions was tested. Planting infester rows of susceptible cultivars (CSH 1 or CSH 5), 20 days before the test material or planting early (40–45 days) flowering lines (IS 802, IS 13429 and IS 24439) along with the test material, split planting of test material at 15-day intervals, grouping test material according to maturity, and use of sprinkler irrigation to maintain high humidity, were found effective in increasing the efficiency of screening and selecting for resistance to head bugs.

A headcage technique to screen for resistance under no-choice conditions has also been developed. Panicles infested with 10 pairs of bugs at pre- and half-anthesis, result in maximum population build-up and grain damage under headcage. This technique is useful for confirming the resistance observed under field conditions.

Under natural infestation, five genotypes harboured relatively lower head bug numbers than the susceptible checks, but only three (IS 17610, IS 17618 and IS 17645) maintained their level of resistance under the headcage. Seed germination was > 70% in these genotypes compared to < 10% in CSH 1 and CSH 5.

Biochemical approaches have been used to enhance the potency of Bacillus thuringiensis against Plodia interpunctelia. Tests were made with different classes of chemical compounds, characterizedby being safe, non-toxic to man, and cheap in price. Among the tested inorganic salts, calcium carbonate, calcium oxide and zinc sulphate were found to increase the potency of B. thuringiensis δ-endotoxin by 2.5-, 1.9- and 2.7-fold, respectively. With the nitrogenous compounds, the amino acids serlne, arginine, alanine and teucine enhanced the endotoxin effect by 52-, 3.6-, 13- and 1.1-fold, respectively. Also, among the protein solubilizing agents, EDTA and sodium thloglycollate led to a 100- and 2.6-fold Increase in the potency. Formic acid was highly effective among the organic acids used in enhancing the potency, followed by malk acid, with 4.8- and 2.4-fold increase, respectively.

Successive extraction of the green alga, Scenedesmus acutus 276–3a with different solvents indicated that the petroleum ether extract was the most repellent to the hatched larvae of Spodoptera littoralis. The application of spray emulsified 1 % petroleum ether extract inhibited egg laying. At 0.25% concentration the moths laid only 52.4 of their egg masses on the treated oviposition sites in comparison to the untreated control. Concentration of 1% was protective against the immature stage by hindering the third instar larvae to feed on treated leaf discs. In addition, the water emulsion of petroleum ether extract was insecticidal. The percentage mortality was directly proportional to the concentration applied and to the duration of exposure.

Soil samples collected from six localities in Pakistan—Peshawar, Quetta, Loralai, Sibi, Lahore and Sheikhupura—were screened for insecticidal Bacillus spp. Bacillus coagulane, B. megaterium and B. alvei, which constituted 50%, 33% and 17% of the Bacillus isolates respectively, were isolated and their toxicity was evaluated against larvae of the house fly, Musca domestica (Diptera: Muscidae). The most toxic bacterial isolate of the three was B. alvei (98.7% mortality) and the least toxic was B. megaterium (89.3% mortality). Extracts of experimental larvae showed the presence of strains of the respective species of Bacillus in all cases, indicating that the observed mortality in the house flies was caused by the Bacillus species.

—A revision of the Neotropical species of the Forcipomyia squamitibia group, revealed three new species, F. (F.) catarinensis from southern Brazil, Colombia and Costa Rica, F. (F.) quechua from northwestern Argentina and F. (F.) rioplatensis from northeastern Argentina and northwestern Uruguay, which are described and illustrated. Forcipomyia (F.) squamitibia Lutz is redescribed from the original type material, a lectotype is designated, and F. (F.) soriai Wirth is recognised as a junior synonym. The remaining known species of this group are diagnosed, and keys to males and females are provided for the identification of the nine recognised species.

This short communication describes the morphological features of three specimens of Hyalomma truncatum which dropped off artificially infested rabbits in the laboratory.

Surveys were conducted in farmers' fields in Zambia during the 1987/88, 1988/89 and 1989/90 cropping seasons, to evaluate the extent of attack on maize by stalk borers and their distribution in some selected maize growing areas in three agroecological regions. Infestation levels varied from season to season. Infestations were low (0.5–13%) in the Southern province: Gwembe Valley and Livingstone in region I and Choma and Kalomo in region II. Infestation levels in other areas ranged from 21–75%. Three species of stalk borers, Busseola fusca, Chilo partellus and Sesamia calamistis were recorded. Their composition and proportion in the complex differed from place to place. C. partellus occurred at an altitude range of 350–1170m, B. fusca occurred at 1032 to >1300m above sea level. B. fusca was the most widely distributed and predominant.