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The legume pod-borer, Maruca testulalis, continues to be a major limitation to successful cowpea cultivation in many countries. During the past decade, research on this insect has increased in scope and intensity at international agricultural research centres and a number of universities. The work that has been done on the biology and control of this pest at the International Institute of Tropical Agriculture (IITA) is briefly discussed with emphasis on the development of a management strategy centred around host plant resistance, and some suggestions for future research direction are given.
Studies on larval movement, feeding and development of Chilo partellus Swinhoe were carried out at Mbita, Western Kenya. Larval movement away from the plant was observed during the first and third instars. Plants inoculated at the stems recorded greater larval migration compared to those inoculated at the leaf whorls. Larval feeding was greater on IS 18363 than on IS 2146, but growth rate, weight gain and efficiency of conversion into body substances were greater in IS 2146. Thus it seems that varietal susceptibility to damage by C. partellus is different from varietal suitability for growth of the larvae.
Microscopic examination of stem tissues damaged during larval feeding revealed that feeding was mainly restricted to the pith and that the vascular bundles were hardly affected.
Paltothyreus tarsatus F. extracts showed anticonvulsant effects in laboratory mice. Chemical examination of Paltothyreus tarsatus revealed the presence of alkyl sulphides (8.5%), ketones (9%), fatty acids (50%), small amounts of alkanes, alkenes and sterol. Constituents were analysed by gas chromatography. Tentative identification of the unknown was confirmed by comparison of its mass spectrometry and its gas chromatography retention time with those of an authentic sample and by co-injection.
Occurrence, abundance and seasonal fluctuations of Culicoides peliliouensis in the mud and sand flats of Hooghly estuary were studied in relation to some important environmental parameters (air temperature, soil temperature, soil moisture, rainfall, salinity, dissolved oxygen and pH of interstitial water, organic carbon, available phosphorus, percentage of sand, silt and clay of soil) at three stations in and around Sagar Island during July 1982 to June 1984. They were more or less found throughout the year, withmaximum abundance during postmonsoon and minimum during premonsoon. Several statistical analyses have been computed to study the relation between population of C. peliliouensis and all ecological parameters. Results of ANOVA indicate that almost all ecological parameters varied significantly over months, stations and years, whereas the population of C. peliliouensis varied significantly only over months and stations. Soil temperature, rainfall, organic carbon and available phosphorus appear to be the major factors controlling their distribution in the intertidal habitat as evident from correlation coefficient analysis. Multiple regression analysis shows that the combined effect of all parameters is positively significant at all the stations.
The effect of light on the development of the angoumois grain moth, Sitotroga cerealella, was studied. Three different light conditions, i.e. continuous light (LL), continuous darkness (DD) and antural illumination (LD), were used.
Eggs bred under LL system showed the shortest mean incubation period, 3.27 and 4.66 days after one and four generations, respectively. The light had no effect on egg hatchability. The number of larvae that reached the adult stage under LL was less (33–36%) than under LD (37–40%) or DD (38%). The fertile females begin egg laying within 0.9 to 2.3 days after mating under all light systems. The shortest period (0.9) was shown under continuous light. The least oviposition period 4.4 and 4.5 was obtained under LL, while the longest period (6.4 and 5.7 days) was obtained under LD, after one and four generations, respectively. The light has no effect on the post-oviposition period. The longest life span of adults was recorded under LD and the shortest under LL. The females bred under LL, laid the least number of eggs (85–87 eggs), while those bred under LD and DD laid the highest number (128–130 for LD and 113–146 for DD, respectively).
The distribution of Oxycarenus gossypinus Distant in artificial temperatures (16.5−40.5°C) and relative humidity gradients (20–95%) was studied in the laboratory. The fifth instar nymphs and adult females showed unimodal distribution to the hot end, a temperature range of 29.0−34.0°C and 31.5−37.0°C, respectively. The adult males showed bimodal distribution, one to the cool end, 19.0−24.0°C and the other to the hot end, 31.5−37.O°C. The adult females significantly moved to low relative humidity (20%) and the males moved in fairly large numbers to both low (20%) and high (95%) relative humidities at the ends of the apparatus with no significant difference in their distribution. O. gossypinus showed stronger response to thigmotaxis (movement to definite end for contact) than to relative humidity gradient, because of significant movement to the corners of the apparatus.
A nuclear polyhedrosis virus isolated from the Egyptian cotton leafworm, Spodoptera littoralis, was found to infect termite castes of Kalotermes flavicollis. Laboratory studies indicated that no specific trend toward mortality responses among the different individuals of termites was noted. All test castes of termites, young, middle-sized, old and reproductive nymphs, and soldiers, were quite equal in their response to the virus infection, regardless of whether the virus concentration was high or low; a concentration of 6.4 × 108 polyhedra/ml, killed only 64% of the treated individuals, while the dosage of 6.4 × 107 polyhedra/ml produced over 90% mortality. Also, thesame trend of response was recorded with the survivors which received challenge doses of NPV suspension each 9 or 10 days. On the other hand, these results revealed that if the NPV is used to control termites, periodic applications would be more efficacious thanone treatment. Virus symptoms were recorded in all affected insects.
Xyleborus ferrugineus (F) was found damaging stored yam tubers, Dioscorea spp. in Nigeria. Infestation starts in November when the tuber moisture is about 62%. The mean developmental period in the tubers was 32 ± 3 days at 30 ± 2°C. Eggs were laid on the tuber surface damaged during harvesting and the first instar larva burrows inside the yam. Storage of undamaged tubers is suggested to prevent losses due to the pest.
Inheritance of resistance to sorghum midge, Contarinia sorghicola Coq. was studied on a set of 21 diallel crosses involving four midge-resistant and three susceptible sorghum, Sorghum bicolor (L.) Moench cultivars under natural midge infestation at Dharwad during the late rainy season (August to November) 1983. Both additive and nonadditive genetic variances were important for midge resistance. The parents, DJ 6514 and TAM 2566, proved as better general combiners. Mean performance of the parents and their general combining ability (GCA) effects were strongly correlated. Crosses with positive specific combining ability (SCA) effects in both F1 and F2 generations had at least one parent with high GCA effects and better per se midge resistance. Midge-resistant parents, DJ 6514 and TAM 2566, with high per se resistance and GCA effects should be utilized in breeding for midge resistance.
Laboratory strain-R of Tribolium castaneum, resistant to lindane and multi-resistant strain-L, having developed resistance to lindane and malathion under field conditions, were compared with the standard susceptible strain-S for the nature of resistance to different groups of insecticides. Lindane resistance in both the strains extended to aldrin, dieldrin, endrin and heptachlor. Unlike laboratory strain-R, resistance did not extend to endosulfan in the field strain-L. Both the strains were found susceptible to p, p′-DDT, methoxychlor and allethrin. Also, lindane resistance did not extend to organophosphorous insecticides, viz., malathion, fenitrothion and dichlorovos. Lindane resistance extended to carbaryl and carbofuran, and only slightly to propoxur in the laboratory strain-R, whereas field strain-L remained susceptible to this group of insecticides. Synergist piperonyl-butoxide was found to overcome cross-resistance to endosulfan and propoxur, but to carbaryl in the lindane resistant strain-R. It is, therefore, indicated that one of the three mechanisms responsible for lindane resistance in the laboratory strain of T. castaneum, was stable in the field strain. Thus, the other two mechanisms showing cross-resistance to endosulfan and carbamates were unstable.
The efficacy of the powder and volatile oil of Piper guineense Schum & Thonn at protecting cowpea against seed beetle, Callosobruchus maculatus (F.) was tested in the laboratory. At low concentrations the powder significantly reduced oviposition and adult emergence while oviposition was completely suppressed at a higher concentration of 42%. The same concentration provided adequate protection for the same amount of cowpea placed in containers of different volumes. The powder, however, did not show any fumigant effect. Volatile oil at 0.002 and 0.005% significantly reduced oviposition and adult emergence, while oviposition was completely suppressed at 0.02% and above. Weight loss of seeds at 90 days after treatment with volatile oil decreased as concentration of the oil increased. The practical significance of the results in small scale storage of cowpea is discussed.
The limit of tolerance to temperature treatments that a developing embryo of Ceratitis capitata is able to withstand without suffering a reduction in hatchability or an increase in late abortions was investigated. Major events during embryogenesis were timed and the observation of the chitinous mouth hook inside unhatched eggs was chosen as a marker of late embryo death. This late abortion production was investigated in three different embryo stages and using two pulse lengths. It was found that an exposure of embryos aged 16 hr after egg laying (right before the beginning of the head involution) to 35°C for a period of 15 hr is close enough but below the limit of tolerance for the strain T (Y-nig+)5038 used in this investigation. Consequently, this exposure is proposed as the discriminating treatment in a screening protocol designed for the isolation of a temperature-sensitive embryonic-lethal mutation.
Experiments carried out in a coffee plantation to determine the developmental period of Icerya paltersoni (Newst.) showed that the female and male scales lasted 157 and 129 days on average, respectively. The different stages of I. pattersoni females were found to be recognizable by the number of antennal segments. The antenna of the stage I nymphal instar is six segmented, stage II is nine segmented and stage III is eleven segmented. The antenna of adult males is eighteen segmented. Females are neotenic but the males possess a pair of grey wings and atrophied mouthparts. In the field the I. pattersoni pest population size is highest in the heavy rainfall months of April and May.
The relative susceptibilities of 43 cowpea varieties to damage by Cydia ptychora (Meyrick) under chemical protection with monocrotophos, were investigated in field trials at Ile-Ife, Nigeria. The results revealed significant varietal differences, with the moderately resistant varieties ER-7, BPL-3-1 and EW/1 consistently showing relatively low damage. These varieties may be useful in planning an integrated pest management programme involving minimum insecticide treatment.
Different concentrations of essential oil of lemon grass, Cymbopogen citratus, were tested for their ovipositional inhibition, antifeedant activity and insecticidal properties against the lesser cotton leafworm, Spodoptera exigua. The results obtained showed that 2% concentration of oil emulsion inhibited egg laying and 0.5% concentration more than reducted by 70% the number of eggs deposited on oviposition sites. 2% concentration acts as a protective concentration against the immature stage by hindering the third instar larvae to feed on treated leaf discs. In addition, the oil emulsion was insecticidal in that percentage mortality was directly proportional to the concentration applied and to the duration of exposure. Older egg masses were more affected by treatment than the newly laid eggs. 2% concentration inhibited hatchability when sprayed on egg masses before hatching. Lemon grass oil effectively controlled S. exigua as an ovicidal and larvicidal agent.
Damage to the antennae was equally common in kings and queens, and was randomly distributed. Damage to the legs was commoner in queens than in kings, and was not randomly distributed. Damage to many or all the legs of one individual may be symptomatic of degeneration due to age.
Studies on seasonal patterns of okra leafhopper, Amrasca biguttula biguttula Ishida were conducted for two years. Time series analyses were adopted for working out weekly seasonal index of okra leafhopper. Low incidence of leafhopper was recorded from June to mid-January. Results further revealed that incidence of leafhopper was highly correlated with minimum temperature. There was no discernible time lag for population increase of leafhoppers. Prediction of leafhoppers at different crop growth stages for various months of sowing was done using dummy variable technique.
Females of Bruchidius atrolineatus (Pic) lay their eggs in the fields on maturing or dry pods of their host plant, Vigna unguiculata. Under experimental conditions in the presence of maturing and dry pods connected with the plant, 80% of eggs are laid on maturing pods. The preference for maturing pods is observed in two generations of B. atrolineatus and varies with the age of females. In the presence of pods separated from the plant, 69% of eggs are laid on dry pods. These results show the importance of methodology during insect behavioural studies. In the absence of choice, reproduction of B. atrolineatus females is more stimulated with dry pods than with maturing ones. These experiments show that factors which influence the choice of the pods are probably different from those stimulating oviposition.
Seven phenolic compounds (phenol, 3- and 4-cresols, 3- and 4-ethylphenols, and 3- and 4-n-propylphenols) previously shown to be components of a fraction of an extract of buffalo urine which was active as a tsetse attractant, were evaluated in field experiments, individually at different concentrations, and in blends. The results indicate that 4-cresol and 3-n-propylphenol are the most important components for the of the attractancy phenolic mixture.