Dynamics ofSitotroga cerealella (olivier) (lepidoptera: gelechiidae) andSitophilus zeamais motschulsky (Coleoptera: Curculionidae) populations in a small bulk of stored corn

The dynamics of Angoumois grain moth, Sitotroga cerealella (Olivier ), and maize weevil, Sitophilus zeamaisMotschulsky , populations breeding in a small bulk (initially 5.36 t) of shelled corn were studied over an 8-year period by monthly sampling. The weevil population showed wide fluctuations in density superimposed on a general decline with time. The moth population showed no upward or downward trend for the first 60 months, although it fluctuated widely. Following a decline that occurred between 56 and 60 months, the moth population fluctuated within a much narrower range, and there was a general decrease in density with time. The decline of the weevil population paralleled deterioration of the corn as did that of the moth population after ca 60 months, and the decline of both species probably resulted from increasing scarcity of suitable breeding sites. Both populations exhibited seasonal variation in density with minima in late summer and early fall, following periods of adversely high temperatures in the storage shed. The populations increased during the fall, leveled off or declined slightly during the winter months, and then increased to maximum levels in late spring or early summer. It thus appears that high temperatures had a greater adverse effect on the populations than low temperatures. The grain moth and the maize weevil both tended to be randomly dispersed at low population levels and moderately aggregated at intermediate and high levels, although the degree of aggregation was not correlated with population density when low population levels were considered separately, and the maize weevil showed a greater tendency for aggregation than did the grain moth. Analysis of individual samples at fixed points in time showed a conspicuous bias for negative correlation between numbers of the two species within sampling quadrats, suggesting a tendency for the two species to segregate within the grain mass. This process could have resulted from behavioral differences or from the destruction of one species by the other. Competitive displacement of the grain moth by the maize weevil has been demonstrated in laboratory experiments but has rarely been observed under natural conditions, and in our study the two species coexisted for 8 years in a relatively small grain bulk.     

The biological bases of resistance in cowpea to the cowpea moth, Cydia ptychora (Lepidoptera: Olethreutidae)

Intensive greenhouse screening using potted plants demonstrated a high level of resistance in the wild cowpea, Vigna unguiculata (ssp. mensensis), to the cowpea moth, Cydia ptychora. Two closely related cvs (TVu 946 and TVu 2994) also showed some resistance. Further investigations in the laboratory and in the greenhouse indicated that resistance was due mainly to oviposition preference and to antibiosis. Pods of the wild cowpea, and those of cvs TVu 946 and TVu 2994, were not attractive to egg-laying females whereas no oviposition preference was seen among the genetically improved cultivars. Pronounced antibiosis was detected in the wild cowpea, and to a lesser extent in the closely related cvs, when pods were infested with first-instar larvae. Fecundity of females was also significantly reduced. These effects were thought to be partly due to nutritional deficiencies in the resistant cvs but there may also be an antibiotic factor in the wild cowpea progenitor. Apparently, pod-wall thickness was not related to resistance although differences in successful penetration of pods by larvae were observed.     

Suitability of five species of stored-product insects as hosts for development and reproduction of the parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae)

We investigated the ability of two populations of Anisopteromalus calandrae (Hymenoptera: Pteromalidae), to parasitize and develop on late instars of five different stored-product insects that typically complete their development inside seeds of grain or legume species or other dry commodity. The host species were the cigarette beetle, Lasioderma serricorne (F.); cowpea weevil, Callosobruchus maculatus (F.); rice weevil, Sitophilus oryzae (L.); lesser grain borer, Rhyzopertha dominica (F.); and Angoumois grain moth, Sitotroga cerealella (Olivier). Experiments were conducted in the laboratory in a no-choice design by using petri dishes (15 by 100 mm) as experimental arenas with 20 host larvae. A. calandrae females from populations originating in Georgia (GA) and Oklahoma (OK) were introduced singly into experimental arenas and allowed to sting and oviposit for 24 h. Parasitism by the OK population was greater than that for the GA population across all hosts. However, no or very low parasitism was found on Angoumois grain moth for either population in this experiment. The highest number of parasitoid progeny was recorded on cowpea weevil (15.9) followed by rice weevil (11.5) and cigarette beetle (10.8) for the OK population. A similar trend was observed in the GA population. The highest proportion of female progeny was produced on cowpea weevil (73.0%) by the OK population. Conversely, a higher proportion of female progeny was produced on rice weevil (64.6%) by the GA population than produced by the OK population. Parasitoid adults were significantly larger and heavier when they developed on cowpea weevil irrespective of parasitoid population. The possible application of these results for biological control of stored-product insects is discussed.     

Integrated Pearl Millet Management in the Sahel: Effects of Legume Rotation and Fallow Management on Productivity and Striga Hermonthica Infestation

Increasing population density and food needs in the Sahel are major drivers behind the conversion of land under natural vegetation to arable land. Intensification of agriculture is a necessity for farmers to produce enough food. As manure is scarce and fertilizers expensive, this study looks into the potential role of cowpea (Vigna unguiculata L.) and short duration fallow in maintaining soil fertility and productivity and in reducing the major weed problem Striga hermonthica (Del.) Benth. The research was carried out ‘on-farm’ in a traditional millet (Pennisetum glaucum (L.) R.Br.) growing area in the Malian Sahel, near Bankass. The four year experiment combined 0, 2, 5, and 7 years of preceding fallow with (i) 4 years of millet, (ii) 1 year of cowpea + 3 years of millet, and (iii) 1 year of cowpea + 3 years of millet/cowpea inter-cropping. Total millet production (4 years) was 1440 kg ha⁻¹ for all systems with 2, 5 or 7 years of preceding fallow against 1180 kg ha⁻¹ for systems without fallow. Cowpea grain production showed no significant differences between fallow treatments. Over 4 years, all cropping systems produced similar total amounts of millet grain, implying that the millet ‘lost’ during the year with a pure cowpea crop in treatments (ii) and (iii) was compensated within three years, while the cowpea grain production was an additional benefit. Such compensation was however not observed for increasing number of preceding fallow years, showing that there is no additional production benefit in 5–7 years of fallow as compared to 2 years.The soil organic carbon content decreased more slowly in treatments with a cowpea pure crop in 1998 than in the millet pure crop, while overall higher contents were observed after preceding fallow also after four years of cropping. Striga hermonthica infestation decreased linearly with duration of preceding fallow, but also after seven years of fallow and one year of cowpea the hemi-parasitic weed still re-appeared. Overall the intensification through a cowpea pure crop and cowpea intercrop in these millet-based systems improved production and a number of other characteristics of the system, making it more viable.Treatments used in the experiments reported here are indicated by the following abbreviations, for further details see text below.     

Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

This paper describes a series of experiments conducted to determine why Sitophilus zeamaisMots . and Sitotroga cerealella (Oliv. ) could not survive together in maize cultures in the laboratory. The effect of S. zeamais on different developmental stages of S. cerealella was investigated. The presence of adult S. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination of S. cerealella by S. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Reduction of insect pest attack on sorghum and cowpea by intercropping

Two experiments to establish the relationship between insect suppression by intercropping and grain yield in sorghum and cowpea were conducted under field conditions. Treatments consisted of monocrops and intercrops of sorghum and cowpea and an additional pair of monocultures and mixtures protected by insecticides. Intercropping reduced the numbers of stem borer,Chilo partellus in sorghum and thrips,Megalurothrips sjostedti in cowpea. In the monocropped, unprotected sorghum, yield was reduced by 28% compared to the protected monocrop, while reduction in the unprotected intercropped sorghum was 15% compared to the protected intercrop. Similarly, in the unprotected cowpea, monocrop yield was reduced by 94% and intercrop yield was reduced by 51%. Thus, there are yield advantages under conditions where intercropping reduces insect pest density. Intercropping can form a component of an integrated pest management programme.     

Decomposition of cowpea and millet amendments to a sandy Alfisol in Niger

Current inputs of organic materials to cropped lands on sandy Alfisols and Entisols in Sahelian West Africa are insufficient to arrest soil organic matter (SOM) decline. Crop residues and green manures require proper management in order to maximize their contribution to nutrient supply and SOM maintenance. The objectives of this study were to quantify the rates of C and N mineralization from cowpea (Vigna unguiculata (L.) Walp.) green manure, cowpea residue, and millet (Pennisetum glaucum (L.) R.Br.) residue under field conditions in Niger and to determine the effect of these organic amendments on pearl millet yield. Millet was grown (1) as sole crop, (2) as intercrop with cowpea, (3) as intercrop with cowpea that was incorporated as green manure during the second half of the growing season, (4) with incorporated cowpea residue (2000 kg ha^–1), (5) with millet residue mulch (3000 kg ha^–1), and (6) with N fertilizer. Carbon loss as CO₂ from soil with and without organic amendment was measured three times per week during the growing season. Nitrogen fertilizer increased millet yield only in a year with a favorable rainfall distribution. Cowpea grown in intercrop with millet during the first part of the growing season and subsequently incorporated as green manure between millet rows increased millet grain yield in a year with sufficient early rainfall, which could be attributed to the rapid rate of decomposition and nutrient release during the first 3 weeks after incorporation. In a year with limited early rainfall, however, densely planted green manure cowpeas competed for water and nutrients with the growing millet crop. Incorporated cowpea residue and millet residue mulch increased millet yield. Surface applied millet residue had high rates of decomposition only during the first 3 days after a rainfall event, with 34% of the millet residue C lost as CO₂ in one rainy season. Recovery of undecomposed millet residue at the end of the rainy season was related to presence or absence of termites, but not to seasonal C loss. Millet residue mulch increased soil organic C content of this sandy Alfisol in Niger. Cowpea and millet residues had a greater effect on SOM and millet yield than cowpea green manure due to their greater rate of application and slower rate of decomposition.     

Effects of water table depth and calcium perioxide application on cowpea (Vigna unguiculata) and soybean (Glycine max)

Summary The effects of three water table (WT) depths (0, 15 and 40 cm) and calcium peroxide (Calper) on the growth and yield of cowpea (Vigna unguiculata, L.) and soybean (Glycine max) were investigated in field lysimeters for a sandy loam soil. Cowpea growth was the best at 40 cm WT depth. Leaf area, plant height, dry matter production, number of leaves and pods, grain yield and consumptive water use of cowpea increases with deeper (lower) WT depth. Application of calcium peroxide improved per cent emergence, leaf area, dry matter, number of leaves and pods, weight of 100 seeds, grain yield and water use in cowpea. The optimum WT depth for vegetative growth of soybean was 15 cm, although the highest grain yield was obtained at 40 cm WT depth. Number of pods, grain yield and water use efficiency of soybean increased with deeper water table depth. Application of calcium peroxide to soybean increased number of leaves and pods per plant, and grain yield for the 15 cm WT depth treatment.     

Effect of maize plants on colonisation of cowpea plants by bean flower thrips,Megalurothrips sjostedti

The effect of non-host maize plants on colonisation of cowpea byMegalurothrips sjostedti (Trybom) (Thysanoptera; Thripidae) was investigated. There were no differences in population density and activity ofM. sjostedti on sole cowpea crop and mixed cowpea/maize crop during the colonisation phase (i.e. 10–30 days after emergence of the plants. However, subsequentlyM. sjostedti numbers were lower in the mixed than in the sole crop, suggesting that maize did not interfere with colonisation of cowpea crop by thrips. In a choice situation, higher numbers ofM. sjostedti oriented towards, and settled on, sole cowpea plants than on those mixed with maize. Olfactory tests indicated that fewer thrips oriented towards a cowpea/maize mixed odour source. When equal numbers of thrips were introduced into the centre of sole- and mixed-cropped cowpea plots, the thrips became randomly distributed in each plot. Fewer thrips were recovered from the mixture than from the sole crop. It is concluded that, although non-host plant odours do not reduce thrips colonisation they interfere with host plant utilisation.     

Effect of cropping systems on cereal stemborers in the cool‐wet and semi‐arid ecozones of the Amhara region of Ethiopia

1 Field experiments were conducted on maize and sorghum at three locations in the Amhara state of Ethiopia to determine the effects of mixed cropping on stemborer infestation, borer natural enemies and grain yields. In the cool‐wet ecozone of western Amhara, sole maize was compared with maize intercropped with faba bean, mustard, potatoes and cowpea. In the semi‐arid ecozone of eastern Amhara, the trial was conducted on both maize and sorghum with the companion crops haricot bean, sesame, cowpea and sweet potatoes. 2 The results showed that the predominant borer species in western and eastern Amhara were, respectively, Busseola fusca and Chilo partellus. In Addis Zemen, western Amhara, maize intercropped with mustard and potatoes had significantly lower pest numbers and percent tunnelling than other intercrops and the maize monocrop during the vegetative stage. In eastern Amhara, the cropping system did not significantly affect pest densities but damage to stem, ear or heads tended to be greatest when cereals were intercropped with sweet potatoes. 3 Parasitism of C. partellus by the braconid Cotesia flavipes was greater on maize than sorghum, and on maize it was greater with sweet potatoes than in other intercrops or sole maize. Cocoon mass number per plant did not vary significantly between treatments. 4 There were significant differences between treatments in yields of both sorghum and maize (per plant and per unit area) with the lowest yields observed when they were intercropped with a tuber crop. 5 The results suggest that simultaneous planting of the crop species selected has little advantage over monocropped maize.     

Suitability of the maize weevil and angoumois grain moth as hosts for the parasitoidsAnisopteromalus calandrae andPteromalus cerealellae

Two parasitoids,Pteromalus cerealellae (Ashmead) andAnisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), were compared for their ability to parasitize two important internally-developing insect pests of stored maize (Zea mays L.). Parasitism byP. cerealellae was greater on Angoumois grain moth,Sitotroga cerealella (Olivier), than on maize weevil,Sitophilus zeamais Motschulsky, in no-choice experiments.Anisopteromalus calandrae parasitized more maize weevils than didP. cerealellae. The former parasitoid parasitized only a few Angoumois grain moths successfully in maize, but parasitized many in wheat if the hosts were younger than 3 weeks old. Thus, both host age and type of grain affect suitability for parasitism. The effects of parental host (species on which the female developed) and experimental host (species exposed to parasitism) on parasitism rate ofP. cerealellae were tested in a host-switching experiment. Parasitism by parasitoids reared on maize weevils was 23% lower than that of parasitoids reared on Angoumois grain moth. This effect was independent of which host the filial generation of parasitoids was tested on. However, the experimental host species had a much greater effect on parasitoid fecundity than the parental host species. Female progeny had smaller body sizes when emerging from maize weevil than from Angoumois grain moth, which may explain the parental host effect on fecundity. There was also a slight intergenerational effect of host species on parasitoid body size.     

The effect of aphid-resistance in cowpea on infestation and development of Aphis craccivora and the transmission of cowpea aphid-borne mosaic virus1

The virus-vector-host relationships of cowpea aphid-borne mosaic virus (CAMV) and its vector, Aphis craccivora, were studied in cowpea lines differing in resistance to aphid infestation. CAMV was acquired and inoculated by its vector during brief probes, confirming that it is non-persistently transmitted. On aphid-resistant cowpea lines, the abundance and the relative sizes of aphids was less than in aphid-tolerant and aphid-susceptible lines. However, aphids were observed to make more numerous probes and probes of shorter duration on aphid-resistant lines than on aphid-susceptible lines. Resistance to aphid infestation in cowpea did not provide resistance to infection with CAMV.     

Insecticidal action of Bauhinia monandra leaf lectin (BmoLL) against Anagasta kuehniella (Lepidoptera: Pyralidae), Zabrotes subfasciatus and Callosobruchus maculatus (Coleoptera: Bruchidae)

Bruchid beetle larvae cause major losses in grain legume crops throughout the world. Some bruchid species, such as the cowpea weevil (Callosobruchus maculatus) and the Mexican bean weevil (Zabrotes subfasciatus), are pests that damage stored seeds. The Mediterranean flour moth (Anagasta kuehniella) is of major economic importance as a flour and grain feeder; it is often a severe pest in flour mills. Plant lectins have been implicated as antibiosis factors against insects. Bauhinia monandra leaf lectin (BmoLL) was tested for anti-insect activity against C. maculatus, Z. subfasciatus and A. kuehniella larvae. BmoLL produced ca. 50% mortality to Z. subfaciatus and C. maculatus when incorporated into an artificial diet at a level of 0.5% and 0.3% (w/w), respectively. BmooLL up to 1% did not significantly decrease the survival of A. kuehniella larvae, but produced a decrease of 40% in weight. Affinity chromatography showed that BmoLL bound to midgut proteins of the insect C. maculatus. 33 kDa subunit BmoLL was not digested by midgut preparations of these bruchids. BmoLL-fed C. maculatus larvae increased the digestion of potato starch by 25% compared with the control. The transformation of the genes coding for this lectin could be useful in the development of insect resistance in important agricultural crops.     

Sensitivity of the common bean (Phaseolus vulgaris L.) symbiosis to high soil temperature

Summary Experiments were done to test whether N fixation is more sensitive to high soil temperatures in common bean than in cowpea or soybean. Greenhouse experiments compared nodulation, nitrogenase activity, growth and nitrogen accumulation of several host/strain combinations of common bean with the other grain legumes and with N-fertilization, at various root temperatures. Field experiments compared relative N-accumulation (in symbiotic relative to N-fertilized plants) of common bean with cowpea under different soil thermal regimes. N-fertilized beans were unaffected by the higher temperatures, but nitrogen accumulation by symbiotic beans was always more sensitive to high root temperatures (33°C, 33/28°C, 34/28°C compared with 28°C) than were cowpea and soybean symbiosis. Healthy bean nodules that had developed at low temperatures functioned normally in acetylene reduction tests done at 35°C. High temperatures caused little or no suppression of nodule number. However, bean nodules produced at high temperatures were small and had low specific activity. ForP. vulgaris some tolerance to high temperature was observed among rhizobium strains (e.g., CIAT 899 was tolerant) but not among host cultivars. Heat tolerance ofP. acutifolius andP. lunatus symbioses was similar to that of cowpea and soybean. In the field, high surface soil temperatures did not reduce N accumulation in symbiotic beans more than in cowpea, probably because of compensatory nodulation in the deeper and cooler parts of the soil.     

Protein and free amino acids in field-grown cowpea seeds as affected by water stress at various growth stages

Summary This study was undertaken to evaluate water stress effects during vegetative, flowering, and podfilling stages of cowpea plants (Vigna unguiculata L.) grown under natural field conditions in southern California on seed yield and protein and free amino acid content of the cowpea seeds. The lowest concentration of N was found in the seeds of the control treatment plants while the seed yield from these treatments was the highest as compared with the N concentration and yield of seeds from plants subjected to water stress during flowering and podfilling stages. The concentration of N in the seeds was inversely related to the seed dry weight yield. Protein arginine,-threonine,-serine,-cystine,-valine,-methionine, and-isoleucine were significantly affected by water stress at the three growth stages. There was no consistent pattern in the effect of water stress on the individual amino acids. The sum of protein amino acids in the cowpea seeds was not significantly influenced by the various treatments since some of the protein amino acids increased and others decreased producing an averaging effect on the figures comprising the sums of the amino acids. Water stress during the flowering and pod-filling stages increased the free amino acid pool, and at the same time, inhibited incorporation of the amino acids into the protein chain-thus lowering the protein amino acid fraction simultaneously. With the exception of methionine plus cystine, the essential amino acids in the seeds were present at concentrations equal to or greater than recommended by the World Health Organization and FAO. It is of particular importance to note that the concentration of lysine in the cowpeas was substantially higher than that found in wheat grain. It is also important to note that the amount of essential amino acids per gram of protein was not measurably affected by the water stress treatments during any of the growth stages.     

Life history attributes of Indian meal moth (Lepidoptera: Pyralidae) and Angoumois grain moth (Lepidoptera: Gelechiidae) reared on transgenic corn kernels

The Indian meal moth, Plodia interpunctella (Hübner), and Angoumois grain moth, Sitotroga cerealella (Olivier), are two globally distributed stored-grain pests. Laboratory experiments were conducted to examine the impact that corn (Zea mays L.) kernels (i.e., grain) of some Bacillus thuringiensis Berliner (Bt) corn hybrids containing CrylAb Bt delta-endotoxin have on life history attributes of Indian meal moth and Angoumois grain moth. Stored grain is at risk to damage from Indian meal moth and Angoumois grain moth; therefore, Bt corn may provide a means of protecting this commodity from damage. Thus, the objective of this research was to quantify the effects of transgenic corn seed containing CrylAb delta-endotoxin on Indian meal moth and Angoumois grain moth survival, fecundity, and duration of development. Experiments with Bt grain, non-Bt isolines, and non-Bt grain were conducted in environmental chambers at 27 +/- 1 degrees C and > or = 60% RH in continuous dark. Fifty eggs were placed in ventilated pint jars containing 170 g of cracked or whole corn for the Indian meal moth and Angoumois grain moth, respectively. Emergence and fecundity were observed for 5 wk. Emergence and fecundity of Indian meal moth and emergence of Angoumois grain moth were significantly lower for individuals reared on P33V08 and N6800Bt, MON 810 and Bt-11 transformed hybrids, respectively, than on their non-Bt transformed isolines. Longer developmental times were observed for Indian meal moth reared on P33V08 and N6800Bt than their non-Bt-transformed isolines. These results indicate that MON 810 and Bt-11 CrylAb delta-endotoxin-containing kernels reduce laboratory populations of Indian meal moth and Angoumois grain moth. Thus, storing Bt-transformed grain is a management tactic that warrants bin scale testing and may effectively reduce Indian meal moth and Angoumois grain moth populations in grain without application of synthetic chemicals or pesticides.     

Effect of spacing in cow pea (Vigna unguiculata) on damage by the black cowpea moth, Cydia ptychora (Lepidoptera: Tortricidae)

Three indeterminate cowpea cultivars with different growth habits were each planted at four inter-row spacings in two different seasons at Ile-Ife, Nigeria, and at harvest assessed for Cydia ptychora damage. Damage by the moth increased with decreasing inter-row spacing much more in the erect and semi-erect cultivars, than in the semi-prostrate cultivar.     

Early generation selection for high yielding cowpea genotypes in additive series intercropping systems with sorghum

Defining appropriate selection strategies for developing cowpea varieties adapted to additive series intercropping systems is an important requirement for cowpea breeders and producers in sub‐Saharan Africa. One hundred and forty‐three F_2:3 cowpea families and their subsequent 99 F_3:4 families derived from a cross between a sole bred cultivar, Apagbaala, and a traditional variety, SARC‐L02, were evaluated under additive series intercropping with sorghum. Intercropping imposed a strong selection pressure for days to flowering such that 31% of F_2:3 families that flowered after 50 days produced too few grains to permit their subsequent evaluation in the F_3:4 generation. Narrow‐sense heritabilities estimated by parent–offspring regression were high for 100 seed weight and days to flowering, moderate for biomass, low for grain yield and insignificant for branches/plant and pods/plant. Retrospective selection at 40% intensity based on F₃ grain yield recovered 5 of the 10 top yielding families in the F₄. No significant difference was observed between mean grain yield of selected and rejected families (at the 40% selection intensity) as estimated by a t‐test. Sole and intercrop yields produced by six advanced breeding lines included as controls showed poor correlation, and suggests selecting cultivars under the target cropping system will produce better selection response.     

Inoculation with arbuscular mycorrhizal fungi enhances growth of Litchi chinensis Sonn. trees after propagation by air-layering

This study investigated the patterns of root growth and water uptake of maize (Zea mays L.) and cowpea (Vigna unguiculata (L.) Walp) grown in a mixture under greenhouse conditions. The plants were grown in root boxes for 5 weeks under 2 watering regimes; fully irrigated and water stress conditions, followed by a 5-day drying cycle imposed during the 6th week of growth. Water uptake patterns were analysed during the drying cycle. The two-dimensional distribution of the roots of both plants in the boxes was determined immediately at the end of the drying cycle. Under well-irrigated conditions, the roots of the component plants grew profusely into all sections of the root box and intermingled considerably. Water stress resulted in the decline of root growth of maize and cowpea but the root:shoot ratios of maize and cowpea were not affected, suggesting that there was no significant effect of water stress on root:shoot partitioning. However, water stress affected the biomass distribution between fine and coarse roots in cowpea. About 64% by weight of cowpea roots under water stress were coarse whereas as against 48% under well-irrigated conditions. Furthermore, water stress generally restricted the lateral extent of the roots of both maize and cowpea with a tendency of clumping together of the root systems and a reduced degree of intermingling. Thus, the extent of mixing of the root systems was apparently controlled by the availability of soil water. Water uptake from the well-irrigated soil in the root boxes was initially restricted to the sections directly below the base of each plant. Although roots of both plants were present in almost all sections of the root box, all the sections did not contribute simultaneously to water uptake by each plant. Water uptake was delayed from the middle intermingled zones. In effect, uptake patterns did not relate generally to the root distribution. The tendency was for the component plants to initially `avoid' water uptake from zones of intense intermingling or competition.     

Photoperiodic,thermal and trophic responses of a predatory ladybird Cheilomenes propinqua

Large geographic range, wide habitat specificity and broad range of prey (including a number of pests of protected crops) suggest that a predatory ladybird Cheilomenes propinqua can be considered as potential agent for biological control in greenhouses. We investigated the influence of day length (10, 12 and 14 hr), temperature (20 and 24°C) and diet (the green peach aphid Myzus persicae and eggs of the grain moth Sitotroga cerealella) on the rate of maturation, fecundity and induction of reproductive diapause in C. propinqua females of a laboratory population originated from Alexandria, Egypt. The proportion of diapausing females (i.e. those with poorly developed ovaries and well-developed fat body) varied from 5% to 70% being higher at short day, low temperature and feeding on the grain moth eggs. This diapause, however, was not very stable: more than 20% of females kept under diapause-inducing conditions started to lay eggs during 110 days, although their pre-oviposition period was about 5 times longer than that of females which matured at the same temperature but at the long day and on the natural diet. Although not very stable, reproductive diapause significantly increased survival of starving females. Such a short-term reproductive diapause can be considered as an adaptation to mild and short-term subtropical winter. The results of our study suggest that C. propinqua mass rearing will be more intensive at the combination of high temperature, natural food (aphids) and long day (14 hr), whereas individuals intended for long-term storage should be reared under moderate temperature (20°C) and short-day (10 hr) conditions and should be fed on factitious food (the grain moth eggs).