Comparative assessment of feeding damage by pod-sucking bugs (Heteroptera: Coreoidea) associated with cowpea, Vigna unguiculata ssp. unguiculata in Nigeria

Feeding trials were conducted on three (young, mid-fill and mature) developmental stages of cowpea Vigna unguiculata ssp. unguiculata pods in the screenhouse using fourth instar nymphs and adults of Anoplocnemis curvipes (Fabricius), Riptortus dentipes (Fabricius), Mirperus jaculus (Thunberg), Clavigralla tomentosicollis St?l and C. shadabi Dolling. Anoplocnemis curvipes was observed to be the most damaging coreoid species causing a yield reduction of 26.4-51.7% followed by R. dentipes (24.4-29.4%), M. jaculus (21.9-26.9%), C. tomentosicollis (17.9-22.4%) and C. shadabi (15.9-20.4%). The fourth instar nymphs of each pod-sucking bug species caused a significantly higher cowpea yield reduction than their respective adults. Similarly, infestation on young pods compared to mid-fill and mature stages resulted in significantly higher yield reduction. The results suggest that infestation levels of two fourth instar nymphs of A. curvipes or three fourth instar nymphs of the other four pod-sucking bug species per young pod should be adequate for screening of cowpea varieties for resistance to the coreoid bugs.     

Reproductive performance of four aphidophagous ladybirds on cowpea aphid, Aphis craccivora Koch

Abstract:  This study investigated prey consumption, egg production, percent progeny loss, reproductive, pre- and post-reproductive periods, reproductive time ratio, reproductive rate and bioconversion efficiency of four aphidophagous ladybirds, viz. Cheilomenes sexmaculata (Fabricius), Coccinella septempunctata Linnaeus, Coccinella transversalis Fabricius and Propylea dissecta (Mulsant) on Dolichos lablab Linnaeus infested with cowpea aphid, Aphis craccivora Koch. C. sexmaculata had the highest bioconversion efficiency, reproductive rate and reproductive time ratio followed in rank order by P. dissecta , C. transversalis and C. septempunctata . This study indicates that C. sexmaculata has a narrow ecological relationship with A. craccivora . The increased allocation of resources to reproduction as indicated through a high reproductive time ratio and high bioconversion efficiency of C. sexmaculata and P. dissecta suggest that they may be better adapted to compete for this prey with larger species like C. transversalis and C. septempunctata .     

Interaction between pod age and position on damage to cowpea Vigna unguiculata by hemipteran pod-sucking bugs

Laboratory and screenhouse studies were carried out to assess the relationship between pod age and pod position of cowpea and damage by different pod bug species. The coreids Clavigralla tomentosicollis St?l and Riptortus dentipes Fabricius caused significant damage to young pods of cultivated genotypes, in contrast to the coreid Anoplocnemis curvipes Fabricius and the pentatomid Aspavia armigera Fabricius which exhibited minor feeding activity. Percent seed damage declined with pod age, the critical stage for pod bug infestation being when pods were about eight days old. Clavigralla tomentosicollis and R. dentipes caused significantly higher damage to pods located within the leaf canopy, thus behaving differently from Anoplocnemis curvipes which showed a distinct preference for pods growing above the leaf canopy. The feeding activity of Aspavia armigera was not affected by the position of pods on the plant. Overall, the study suggests that cowpea genotypes with a short flowering period and pods held above the leaf canopy offer the most promise in the management of pod-sucking pests.     

The effect of past and current hosts on reproductive investment by the adult cowpea aphid Aphis craccivora

Abstract 1. A general index of accumulated investment that alate aphids make into reproduction with respect to environmental changes (specifically changes in host at adult moult) was investigated to determine whether and how reproduction in Aphis craccivora Koch changes once aphids migrate to a different host from the one on which they were born and reared. The aphids were monitored for 4 days to determine the immediate effects of a change in host.
2. A general index of accumulated investment defined as reproductive index was used; reproductive index is equal to the reproductive output (weight of nymphs born; actual fecundity) plus potential reproduction (weight of embryos within the ovarioles with red eye spots; future fecundity).
3. The results revealed that reproductive index is affected by adult weight. The host on which the aphids have been born and reared (source host) has no effect on reproduction other than its influence on adult weight.     

Efficacy of neem and diatomaceous earth against cowpea aphids and their deleterious effect on predating Coccinelidae

Philippine vegetable farmers commonly use synthetic insecticides to control insect pests on yardlong beans ( Vigna unguiculata ssp. sesquipedalis ). An important pest on yardlong beans is the cowpea aphid, Aphis craccivora Koch. Overuse of chemical insecticides and the adverse consequences for farmer health and for the environment have been reported. The natural enemies of A. craccivora , such as the coccinelidae beetle, Menochilus sexmaculatus (Fabr.), do not provide economic control on their own. In the present study the efficacy of the biological insecticide neem (both commercial and homemade) alone, and in combination with diatomaceous earth against A. craccivora was evaluated. The same insecticides were also examined to investigate their deleterious effect on M. sexmaculatus . The efficacies of different treatments with biological insecticides were compared with the use of the synthetic insecticide Hostathion (triazophos). Experiments were conducted under Philippine lowland conditions during the dry season when the occurrence of pest problems in yardlong beans is very great. Commercial neem, NeemAzal-T/S (Trifolio-M GmbH, Lahnau, Germany), significantly reduced the number of A. craccivora . NeemAzal-T/S and diatomaceous earth in combination produced the best control of A. craccivora and were less toxic to M. sexmaculatus than treatment with Hostathion (triazophos). Aqueous homemade neem solution did not control the A. craccivora populations.     

The cowpea aphid, shape Aphis craccivora, host plant odours and pheromones

Olfactometer experiments were conducted with apterae and alatae of the cowpea aphid, Aphis craccivora, Koch (Hom.:Aphidoidea). The occurrence of density dependent related pheromones and odour response to their host plant Vigna unguiculata was studied. Apterae responded with positive anemotaxis to air passed over both small groups of apterae and alatae (10 individuals) but negatively to air that passed over a bigger group (20 individuals). Alatae responded in the same way to groups of apterae but were repelled by alatae independent of the size of the group applied as odour source in the olfactometer, except when exposed to air passing ten alatae feeding on cowpea leaves. This may be due to interaction between aphid pheromones and host plant odour. Both apterae and alatae showed a general attraction to green plants and were also able to distinguish between other host plants and cowpea, which was the original host of the aphid clone used in the experiments. When attacked by aphids, the cowpea plant responded with a temporal increase in attractivity that reached a maximum after 48 h and had disappeared after one week.     

Functional response of the ladybird, Cydonia vicina nilotica to cowpea aphid, Aphis craccivora in the laboratory

The functional response of Cydonia vicina nilotica Muls. （Coleoptera： Coccinellidae） to six densities of Aphis craccivora Koch （Homoptera： Aphididae） nymphs on broad bean （Viciafaba Linn.） was investigated in the laboratory. A linear relationship between the rate of consumption and prey density was observed with r^2 values between 0.58 and 0.97. Plotting prey density against prey killed by four larval instars, and adult males and females of C. vicina nilotica fit well with the type Ⅱ model of Holling＇ s disc equation. Adult females consumed the highest number of prey, followed by fourth instars and adult males. Based on the functional response data, the model predicts a maximum of 144.9, 116.3, 86.2, 80.0, 72.5 and 20.0 nymphs to be consumed per day by an individual adult female, fourth instar, adult male, third, second and first instars, respectively. The differences in the responses of the predator to aphid densities are discussed.     

Resistance to the cowpea weevil (Callosobruchus maculatus) larva in pods of cowpea (Vigna unguiculata)

Thirty cowpea, Vigna unguiculata (L.) Walpers, cultivars were evaluated as intact pods to determine if any possessed resistance to the cowpea weevil, Callosobruchus maculatus (Fabr.). Pod resistance was measured as pre-establishment larval mortality (PreM); those larvae dying after egg hatch but before penetrating into the seeds, and as post-establishment within-seed mortality (PostM); those larvae dying after penetrating into the seeds. Among the 30 varieties examined, PreM ranged from 57.9% to 99.4% and PostM ranged from 6.7% to 82.6%. Ten varieties exhibited total intact pod mortality (mortality from egg hatch to adult emergence from the seed) greater than 95%.Physical measurements were made of several pod and seed characteristics to ascertain whether the observed pod resistance was due to seed factors, pod-wall factors, or to interactions between the pod and seeds. Although resistance to breakage (from handling plus pod dehiscence) is a necessary characteristic for overall pod protection against C. maculatus; other factors are also important. Among the other pod and seed characteristics measured to identify major resistance factors, seed coat thickness was the one most highly correlated with pod resistance. Our results suggest that interactions between pod-wall and seed coat characteristics play a large role in pod resistance of cowpeas to C. maculatus.     

Epidemiological studies of Colletotrichum gloeosporioides disease of cocoa

The intensities of foliar infection (leaf blight and shot hole) and pod rot, caused by Colletotrichum gloeosporioides, were recorded from a cocoa-areca mixed garden and a cocoa-monocrop garden during 2 years. The intensity of pod rot was recorded from both the gardens. The intensities of leaf blight and shot hole gradually increased from July, reached a peak during September-November, decreased thereafter and reached the lowest level during April-June. Increase in leaf infection was associated in both plantings and in both years with the period of rain (June-November). The phylloplane population of C. gloeosporioides also increased during June-November when the temperature tended to be low and constant with high rainfall and relative humidity. During this period there were few susceptible stages of pods (cherelles and young pods) and pod infection was very low. Nearly mature pods were free from infection. I n both years, pod infection was more in the cocoaareca mixed garden than' in the cocoa-monocrop; it was observed during January-May, when the susceptible stages were mostly prevalent but when the C. gloeosporioides population was low and the climatic factors appeared to be relatively unfavourable. This may be one reason for the lesser incidence of pod rot when compared to foliar disease.     

Inheritance of resistance to the cowpea aphid in cowpea

Summary Inheritance of resistance to cowpea aphid, Aphis craccivora Koch, in three resistant cultivars of cowpea, Vigna unguiculata (L.) Walp, was studied. The parents, F₁ and F₂ population were grown in an insect-proof screenhouse. Each 3-day-old seedling was infested with 10 apterous adult aphids. Seedling reaction was recorded when the susceptible check was killed. The segregation data revealed that the resistance of ICV11 and TVU310 is governed by single dominant genes. All the F₂ seedlings of the cross ICV10xTVU310 were resistant, indicating that they have the same gene for resistance. However, the F₂ populations from the crosses ICV10xICV11 and ICV11xTVU310 segregated in a ratio of 151, indicating that the dominant genes in ICV11 and TVU310 are non-allelic and independent of each other. The resistance gene of ICV10 and TVU310 is designated as Ac₁ and that of ICV11 as Ac₂.     

Nitrogen nutrition and metabolic interconversions of nitrogenous solutes in developing cowpea fruits

Budgets for import and utilization of ureide, amides, and a range of amino acids were constructed for the developing first-formed fruit of symbiotically dependent cowpea (Vigna unguiculata [L.] Walp. cv Vita 3). Data on fruit total N economy, and analyses of the xylem and phloem streams serving the fruit, were used to predict the input of various solutes while the compositions of the soluble and protein pools of pod, seed coat, and embryo were used to estimate the net consumption of compounds. Ureides and amides provided virtually all of the fruit's N requirements for net synthesis of amino compounds supplied inadequately from the parent plant. Xylem was the principal source of ureide to the pod, while phloem was the major source of amides to pod and seed. All fruit parts showed in vitro activity of urease (EC 3.5.1.5), allantoinase (EC 3.5.2.5), asparaginase (EC 3.5.11), ammonia-assimilating enzymes and aspartate and alanine aminotransferases (EC 2.61.1 and EC 2.6.1.1.2). Asparagine:pyruvate aminotransferase (EC 2.6.1.14) was recovered only from the pod. The pod was initially the major site for processing and incorporating N; later seed coats and finally embryos became predominant. Ureides were broken down mainly in the pod and seed coat. Amide metabolism occurred in all fruit organs, but principally in the embryo during much of seed growth. Seed coats released N to embryos mainly as histidine, arginine, glutamine, and asparagine, hardly at all as ureide. Amino compounds delivered in noticeably deficient amounts to the fruit were arginine, histidine, glycine, glutamate, and aspartate, while seeds received insufficient arginine, histidine, serine, glycine, and alanine. Quantitatively based schemes are proposed depicting the principal metabolic transformation accompanying N-flow between seed compartments during development.     

Diurnal water balance of the cowpea fruit

The vascular network of the cowpea (Vigna unguiculata [L.] Walp.) fruit exhibits the anatomical potential for reversible xylem flow between seeds, pod, and parent plant. Feeding of cut shoots with the apoplast marker acid fuchsin showed that fruits imported regularly via xylem at night, less frequently in early morning, and only rarely in the afternoon. The dye never entered seeds or inner dorsal pod strands connecting directly to seeds. Root feeding (early morning) of intact plants with ³²PO₄ or ³H₂O rapidly (20 min) labeled pod walls but not seeds, consistent with uptake through xylem. Weak subsequent (4 hours) labeling of seeds suggested slow secondary exchange of label with the phloem stream to the fruit. Vein flap feeding of subtending leaves with [¹⁴C]sucrose, ³H₂O, and ³²PO₄ labeled pod and seed intensely, indicating mass flow in phloem to the fruit. Over 90% of the ¹⁴C and ³H of fruit cryopuncture phloem sap was as sucrose and water, respectively. Specific ³H activities of transpired water collected from fruits and peduncles were assayed over 4 days after feeding ³H₂O to roots, via leaf flaps, or directly to fruits. The data indicated that fruits transpired relatively less xylem-derived (apoplastic) water than did peduncles, that fruit and peduncle relied more heavily on phloem-derived (symplastic) water for transpiration in the day than at night, and that water diffusing back from the fruit was utilized in peduncle transpiration, especially during the day. The data collectively support the hypothesis of a diurnally reversing xylem flow between developing fruit and plant.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17 °C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17 °C to27 °C strongly reduced pod production, mature pod size andseeds per pod, while an increase in day temperature from 22°C to 32 °C had smaller and less consistent effects.Pod production under high night temperature was not constrainedby flower production since 27 °C at night promoted branchingand flower bud appearance. Under 32/27 °C day/night temperaturethe large reduction in pod set was due to enhanced abscissionof flower buds, flowers and young pods (< 3 cm). Flowershad the highest relative abscission followed by young pods andflower buds. Therefore, the onset of anthesis and of pod developmentwere the plant stages most sensitive to night temperature. Podslarger than 3 cm did not abscise but usually aborted and shrivelledunder high night temperature. The effects of 32/27 °C werenot due to transient water stresses and were observed even undercontinuous irrigation and mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L., cv. Tenderette     

Control of dark leaf spot (Alternaria brassicicola) of Brassica oleracea seed production crops with foliar sprays of iprodione

Three sprays of iprodione (Rovral 50% w. p.) at 0.5-1 kg a. i./ha applied to Brassica oleracea seed crops in experimental plots and field trials at 3-wk intervals from the young green pod stage until cutting controlled pod infection caused by A. brassicicola in seasons 1976–1979. As a result few seeds were infected, seed yields were increased and their germination was improved. Sprays of Bordeaux mixture were as effective as iprodione in years when disease levels were low but were ineffective when infection pressure was severe.     

Interactive effects of high temperature and elevated carbon dioxide concentration on cowpea [Vigna unguiculata (L.) Walp.]

Limitations in carbohydrate supplies have been implicated as a factor responsible for reproductive failure under heat stress. Heat stress affects two stages of reproductive development in cowpea [Vigna unguiculata (L.) Walp.], and genotypes are available with tolerance and sensitivity to heat during these different stages. The objectives of this study were to determine the responses of these cowpea lines to ambient and elevated [CO₂], under heat stress and optimal temperature, and test whether differences in carbohydrate supplies due to genotypes, CO₂ enrichment and heat stress are associated with differences in sensitivity to heat during reproductive development. Plants were grown in reach-in growth chambers and subjected to day/night temperatures of either 33/20 or 33/30°C, and [CO₂] levels of either 350 or 700 μmol mol^-1. Under intermediate night temperature (33/20°C), all lines set substantial numbers of pods. Under high night temperature (33/30°C) with either ambient or elevated [CO₂], one heat-sensitive line produced no flowers and the other set no pods, whereas the heat-tolerant line abundantly set pods. High night temperature reduced the overall carbohydrate content of the plants, especially peduncle sugars, and caused decreases in photosynthetic rates. The high pod set of the heat-tolerant line, under high night temperature, was associated with higher levels of sugars in peduncles compared with the heat-sensitive lines. The heat-tolerant line accumulated substantial shoot biomass, exhibited less accumulation of starch in leaves, and possibly had less down-regulation of photosynthesis in response to CO₂ enrichment and heat stress than the heat-sensitive lines. Elevated [CO₂] resulted in higher overall carbohydrate levels in heat-sensitive lines (starch in leaves, stems and peduncles), but it did not increase their heat tolerance with respect to flower production or pod set. Heat-induced damage to floral buds and anthers in the sensitive lines was associated with low sugars levels in peduncles, indicating that heat had greater effects on assimilate demand than on leaf assimilate supply. The heat-tolerant line was the most responsive genotype to elevated [CO₂] with respect to pod production under either high or intermediate temperatures.     

Field resistance in cowpea, Vigna unguiculata to the cowpea moth, Cydia ptychora

Field evaluation of 26 selected cowpea cultivars showed that several of them had good levels of resistance to Cydia ptychora; TVu 946, Adzuki, ‘Vita 5’ and Igbirra were the most resistant. Percentage seed damaged by the larvae was positively correlated with days to 50% flowering (r= 0.39*), days to 50% pod ripening (r= 0.48*) and weight of 100 seeds (r= 0.56**). All four cultivars were early maturing, had semi-determinate or determinate plant types and carried their pods above the leaf canopy. No single morphological character could be related to the degree of seed damage but some association with phenological characteristics was indicated. Earliness, determinacy and uniform pod maturity were important plant characters associated with the expression of field resistance. Even if these characters are not causative, they provide a rational basis for screening of a large germplasm to identify or synthesise materials with greater resistance to this moth.     

Economic threshold for soybean aphid (Hemiptera: Aphididae)

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d +/- 0.8 d (mean +/- SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 +/- 38 (mean +/- 95% confidence interval [CI], range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 +/- 95 (mean +/- 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.     

Numerical response of ladybird beetles (Col., Coccinellidae) to aphid prey (Hom., Aphididae) in a field bean in north-east India

Two predaceous species of Coccinellidae, Menochilus sexmaculatus and Coccinella transversalis , occurred abundantly in bean crops infested with the aphid, Aphis craccivora Koch in north-east India. The number of eggs and adults of the two coccinellids increased in response to the increase in the population of aphid prey. Reproductive numerical responses were found to be synchronous to prey density whereas aggregative numerical responses appeared asynchronous in the later part of the aphid cycle on beans. Menochilus sexmaculatus oviposited smaller clusters of eggs at lower density of aphids than C. transversalis which laid larger clusters and showed greater numerical response at higher densities of aphids. Within a species cluster the size of the eggs seems to be directly related to aphid density. The two coccinellid species of this study seem to be efficient predators of A. craccivora in terms of their reproductive and aggregative numerical responses.     

Comparative study on the efficacy of neemix and basil oil formulations on the cowpea aphid Aphis craccivora Koch

Both neemix and basil oil had an insecticidal effect against Aphis craccivora Koch when the plant was treated systematically or by contact. The tested compounds caused a significant reduction in fecundity, longevity and the natal period. In addition, neemix and basil oil had a toxic effect on the adult stage of the pest, which was more clear for basil oil than neemix, since the cumulative percent morality reached 100% in all tested concentrations after 7 days for basil treatment and after 8 days for neemix oil treatment, while the mortality did not exceed 36% for the control. The two tested oils also had an antifeedant and aphicidal effect on the nymphal stage, since they caused prolongation of the nymphal duration, high percentage of mortality and only a few young ones can be succeeded to reach to the adult stage. The correlation between the biological effects of the tested compounds and the impairment of the activity of some enzymes (acid phosphatase and alkaline phosphatase) and (aspartate aminotranferase and alanine aminotransferase) as well as protein contents had also been investigated. The results clarified a significant reduction in all the tested enzymes and were more pronounced for basil oil treatment than neemix. This explained the reduction in the reproductive potency of A. craccivora Koch. Concerning the side effect of the tested compounds on faba bean plants, the results indicated that the treatment induced promising effect on the antioxidant enzymes activity (superoxide dismutase, catalase, peroxidase and polyphenol oxidase) of the plants which were treated with basil oil and neemix.     

水分亏缺对蚕豆光合特性影响的初步研究

本文报道了蚕豆现蕾至饱荚期不同时间土壤水分亏缺情况下的光合特性、光合产量及蚕豆水分亏缺敏感期。蚕豆现蕾后给予土壤干旱处理,光合速率、叶绿素含量、叶面积、气孔开度、生物产量及籽粒产量下降,但气孔密度和呼吸速率增加。水分亏缺使叶片光饱和点由50kLx降至30kLx,气孔开度日变化呈单峰(9—11时)曲线。始荚至盛荚期对土壤干旱最敏感,此期是蚕豆灌水的关键时期。