The effect of N, P and K fertilisers, measured as percentage leaf dry matter, was assessed on larval populations of Maruca testulalis (Geyer) (Lepidoptera: Pyralidae) recorded on cowpea, Vigna unguiculata, var. IT 82E-32 under natural infestation. The study was carried out during the 1987 long rains (March-July), at Abomey-Calavi's experimental farm. A factorial experiment with 9 completely randomised treatments in three replicates of N-P-K fertilisers was used. Phosphorus was applied at three levels (P0, P1, and P2) corresponding to 0, 40 and 80 kg of P2O5/ha respectively. Potassium was also applied at three levels (K0, K1 and K2) representing 0, 40, and 80 kg K2O/ha respectively. In all plots nitrogen was applied as 20 kg /ha of urea. All the fertilisers were spread on the soil on the day of planting. Fourteen sampling dates for flushing shoots, flower buds, flowers and pods were subsequently made 29, 33, 36, 40, 43, 47, 50, 54, 57, 61, 64, 68, 71 and 75 days after sowing (DAS) to evaluate the infestation rate by M. testulalis larvae. Sampling for. N, P and K contents in cowpea leaves was conducted 29, 47 and 61 DAS. As for interaction between P and K and the pest, only the averages of larvae from interaction P0 K0, P2 K0 and P0 K1 on the one hand, and those from the interaction of P0 K0, P0K2 and P0K2 on the other hand, were statistically, (P < 0,05) different. Multiple regression analysis showed that the content of N, P and K in cowpea leaves throughout the sampling period influenced by 40% the total variation of larval population of M. testulalis in the plant. The remaining 60% were due to other factors of experimental agrosystem. Application of N, P and K fertilisers to the cowpea and their assimilation by the plant are primarily aimed at increasing the plant vigour and grain yield. In contrast, the plant vigour induced by these nutrients leads to an increase in the larval population of M. testulalis in the plant and also to a decrease in the highest yields that can be expected from the use of these fertilisers. Therefore, an agrobiological competition takes place as a result of two inductive opposite effects inherent from fertilisation. In connection with this situation, the control of M. testulalis using fertilisers could be one option to maintain a buffer effect between the pest and the plant, thus therefore help in increasing cowpea yield.

The legume pod-borer, Maruca testulalis was reared in the laboratory for 10 successive generations using a semi-synthetic diet. The diet was composed of locally available soybean flour and cowpea flower powder as basal ingredients. The artificial medium was as suitable as the cowpea host plant for M, testulalis in supporting larval growth and development. Fecundity increased with advancing generations on the artificial medium. Field collected pupae were heavier than diet-reared pupae. However, the fecundity, fertility, adult life span, and sex ratio did not differ between the two rearing regimes. The laboratory-reared insects were of acceptable uniform quality and predictable performance even after 10 successive generations of laboratory rearing. Adult emergence ranged between 70–90%. One litre of diet produced on average 400 pupae or adults with a mean fecundity of 200 eggs per female. One person working 8 hr/day can produce a minimum of 1000 healthy pupae or adults daily. The laboratory rearing management protocol is described.

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.

Field studies to investigate the effect of intercropping on the relative resistance and susceptibility of cowpea cultivars to Maruca testulalis impure stands and intercropped with maize, were conducted at the International Centre of Insect Physiology and Ecology (ICIPE). It was clearly indicated that intercropping affected the relative resistance and susceptibility of cowpea cultivars. The resistance of TVU 946 to Maruca was reduced when the cultivar was under maize. This was attributed to the phenological changes observed, i.e. when planted with maize there was a significant (P = 0.05) increase in length of the pods and peduncles and significant (P = 0.05) reduction in the number of branches. Weekly mean temperatures and relative humidities indicated that there were significant differences between cropping patterns. Similarly there was a significant reduction in the photosynthetic active radiation incident on cowpea canopy in all the intercropped plots. This suggested that both intercropping and microenvironmental differences observed, reduced resistance in cultivar TVU 946 by probably acting directly on the crop, thus rendering it more susceptible.

The anatomical and biochemical basis of resistance of Vigna vexillata (Benth) (Ace. TVNu 72) to Monica testulalis were investigated. An uncharacteristic network of fibrous structures was observed on the petal surface of TVNu 72 but not on those of the susceptible control, IT82D-716. Stems of TVNu 72 and IT82D-716 have thick and closely packed collenchyma cells. Both varieties have been identified as possessing resistance to stem feeding; however, IT82D-716 is susceptible to flower and pod damage. The distance between pod wall epicarp and mesocarp was significantly (P ≺ 0.05) smaller in IT82D-716, but cell and tissue arrangement were similar for both varieties.

Total sugar content in the pod wall and seed of TVNu 72 was higher (P ≺ 0.05) than in IT82D-716. Phenol content was lower (P ≺ 0.05) in the pod wall of TVNu 72 but the reverse was true for fresh and dry seeds. This suggests that neither phenol nor total sugar are involved in the resistance of TVNu 72 to M. testulalis. However, it seems that thick and compact collenchyma cells in the stems and Fibrous tissues on the petal surface contribute to the resistance in TVNu 72. The results are discussed in line with previous reports which indicate that trichomes are the principal factors in the resistance of TVNu 72 to M. testulalis.

The effects of plant growth habit (erect versus spreading and flowering pattern) on the resistance of cowpea Vigna unguiculata (L.) Walp., to the legume pod borer, Maruca testulalis Geyer, were studied in Nigeria. Five cowpea cultivars of known agronomic and architectural characteristics were selected for the study: TVu 946, IT82D-716, VITA-3, Oloka local and Kamboinse local. Seed and pod damage assessment values were better in profuse flowering than in non-profuse flowering cultivars and in erect cultivars than in spreading cultivars. Best performances were obtained from TVu 946 (profuse flowering and erect resistant), and worst results from Oloka local (spreading susceptible) and VITA-3 (susceptible non-profuse) respectively. Erect and profuse flowering cowpea cultivars are proposed as having good architectural components for reducing M. testulalis damage to cowpea. The implications of architectural variations in cowpea are discussed.

The possibility of the involvement of pod wall toughness in the resistance of cowpea, Vigna unguiculata (L.) Walp., to the legume pod borer, Maruca testulalis was studied. The toughness of non-intact and intact pod wall increased with age, but the rate varied at different growth stages of the pod as well as between cultivars. There was a positive and significant correlation (r = 0.82**) between pod age and pressure required to penetrate pod wall. No significant differences (P > 0.05) were observed in non-intact pod wall toughness between TVu 946 (resistant) and IT82D-716 (susceptible) at all the growth stages tested. However, significant differences (P < 0.05) were observed between these two cultivars for only 6-day-old intact pods where IT82D-716 recorded a higher value than TVu 946. Correlation between pod damage severity by M. testulalis and toughness of non-intact and intact pod wall of these cultivars at different growth stages were not significant.

While pod wall toughness would be a desirable trait, it is concluded from this study that pod walls of the cultivars studied did not play any appreciable role on cowpea resistance to the larvae of M. testulalis.

The effect of pod angle on the resistance of cowpea, Vigna unguiculata (L.) Walp. to the legume pod borer, Maruca testulalis Geyer, was investigated under field conditions at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, using two cowpea cultivars: IT82D-716 (susceptible to borer damage) and TVu 946 (resistant to borer damage). Three different pod angles were used In the study — a normal angle, a decreased angle and an increased angle. Negative and highly significant (P < 0.01) relationships were found between pod angle and per cent pod damage, as well as the seed damage Index In the two cowpea cultivars. Pods with wide angles (≥ 89°) were damaged on only one and rarely on both pods. Apart from biochemical and other bio-physical factors, selection and breeding for wide pod angle is suggested as a strategy for reducing M. testulalis damage to cowpea pods.

Data from regular field samples throughout the life cycle for five generations of the legume pod borer, Maruca testulalis on cowpea crops at one site, and three generations at another, were used to construct life tables and through key factor analysis to determine the key mortality factor. The total mortality from egg to adult was 98.4–98.6% at site 1 and 98.2–99.4% at site 2. At both sites the highest mortality occurred between the eggs and the third instar larvae, whilst the fourth instar larvae suffered the lowest mortality. The commonest cause of mortality was classified as disappearance, followed by disease. Parasitism contributed minimally to M. testulalis mortality. At site 1 disappearance at the egg stage was the key mortality factor and was significantly correlated with the total generation mortality. At site 2, disappearance operating at the larva 1 and 2 stage was tentatively identified as the key mortality factor. The data from site 1 showed no significant correlation between population density and mortality at the same stage. This study provides the first detailed analysis of M. testulalis populations and should contribute towards developing control strategies for this important pest of cowpea.

The effects of cowpea, Vigna unguiculata (L.) Walp. canopy structure and pod position in relation to infestation and damage by the legume pod borer, Maruca testulalis Geyer were investigated. Defoliated cultivars sustained significantly less infestation and damage (P < 0.05) than those undefoliated. Relative humidity measured under the canopy was lower in defoliated cultivars, while soil and ambient temperatures were higher. Percentage pod damage and larval infestation by M. testulalis in flowers were positively correlated with relative humidity, and negatively correlated with temperature. Both correlations were significant (P < 0.01).

Cultivars with pods held within the canopy suffered significantly more damage (P < 0.05) than cultivars whose pods were held in the normal position. Canopy structure and pod position acting together or independently, exerted profound effects on cowpea resistance to M. testulalis. Selection and breeding cowpea cultivars with less dense foliage (= open canopies) and long peduncles holding the reproductive structures above the canopy, should increase cowpea resistance to M. testulalis.

Anatomical features of cowpea (Vigna unguiculata) associated with stem and pod wall resistance to the legume pod borer, Manica testulalis, were studied. The anatomical microenvironment of the area immediately post the stem epidermis seems to impose severe limitation to larval movement and feeding within the tissue. Collenchyma cells in both 21-day old TVu 946 and IT82D-716 stems form a network of closely knit interlocking cells with a few intercellular spaces. Significant differences (P < 0.05) were observed in the distance between the epidermis and collenchyma cells of the slightly raised (convex) and concave portions of TVu 946 and IT82D-716 stems. TVu 946 had a smaller stem diameter than IT82D-716 stem. Distance between epicarp and mesocarp tissues of 7-day old TVu 946 and IT82D-716 pod wall did not show any significant difference. Similarity in cell and tissue arrangement and the absence of strengthening tissues in pod wall could be some of the most important constraints responsible for their vulnerability to larval damage.

Stem anatomy is considered to be an important factor in stem resistance to M. testulalis, but this does not appear to be the case in pod wall resistance.

Studies at ICIPE's Mbita Point Field Station (site 1) and a farmer's field in Lambwe Valley (site 2) in Western Kenya, revealed the presence of at least seven parasitoids, two predators, one nematode and several microorganic pathogens attacking Maruca testulalis on cowpea crop. Some parasitoids and pathogens were also recovered from M. testulalis cadavers collected on wild host plants of the pest. A pupal endoparasitoid, Antrocephalus sp. was the most predominant, while the pathogens Nosema sp. and Bacillus sp. caused the highest natural mortality on M. testulalis in this region.

Parasitoids and pathogens contributed 40.65 and 35.6% to the total generation mortality (K) at sites 1 and 2 respectively. Observed parasitism only contributed 3.25% at site 1 and 3.8% at site 2 of the generation mortality. Mortality due to disappearance which included predation accounted for 59.35 and 64.8% of K at the respective sites. Life table data and survival curves for the pest revealed high generation mortality (ca. 98%), most of which occurred in the early life stages of the pest. The results suggest a high potential for utilizing biocontrol agents in IPM of the pest.

Neem oil (NO), and different formulations of neem oil in a solution of Tetrapleura tetraptera as emulsifier, including neem oil emulsifiable concentrate (NOEC), neem oil slurry emulsifiable concentrate (NOSEC) and 5% NOEC obtained from the seeds of the neem plant, were tested for their efficacy in the control of Maruca testulalis Geyer, under laboratory conditions using flowers of Ife Brown, cowpea variety.

The different concentrations of NOEC (5, 10 and 20%) exhibited a high degree of insecticidal activity on M. testulalis larvae. All the treated flowers were protected from larval damage 2 days after treatment as compared to the 100% damage recorded on untreated flowers and on the flowers treated with T. tetraptera solution alone.

The NOSEC and the 5% NOEC prepared using different volumes of the emulsifier also exhibited some insecticidal activity which decreased with a decrease in concentration. NO/NOEC were superior to NOSEC and the 5% NOEC prepared in different volumes of the emulsifier.

Larvae of Maruca testulalis were found to be randomly dispersed on flowers of cowpea cultivar Vita 1. Three models based on Taylor's power law, Lloyd's mean crowding and the negative binomial were tested to find out the best fit for developing a sequential sampling plan for this pod borer. Taylor's power law model gave the best fit whilst the negative binomial gave the least. A sequential sampling plan and a table of optimum sample size for use in the field were therefore developed, based on the random distribution.

The anatomy of damaged and undamaged young stem, peduncle and young pods were examined from transverse sections in three varieties of cowpea in order to evaluate the anatomical basis of resistance to the pod borer Maruca testulalis.

While tissue development in the stem, peduncle and pods of the three varieties of cowpea were similar, the relative thickness of the various tissues were different in the order Vita-1>ICV-2>TVu 946. The smaller diameter and the relative abundance of strengthening tissues in the stem and peduncle of TVu 946, by limiting total ingestible biomass, might be restricting the damage to these organs by the pod borer.

Pod damage, on the other hand, was concentrated on the parenchymatous tissue of the pod wall lining and inter-seed spaces and the sizes of this tissue were also different among the varieties in the order Vita-1>ICV-2>TVu 946, the same order of susceptibility to attack by M. testulalis.

A schedule of insecticide spray combining two insecticides: Decis®(deltamethrin) and Systoate® (dimethoate) with four times of spray: 35, 45, 55 and 65 days after planting (DAP) was investigated in order to search for the most effective treatment against Maruca testulalis (Geyer) population on cowpea (Vigna unguiculata (L.) Walp). The local cowpea cultivar “Kpodjiguegue” was used to study the onset and fluctuation of M. testulalis larvae infestation on cowpea terminal shoots, flowers and pods. The trial was carried out during the 1985 early cropping season at Abomey-Cala vi. The treatments' effect on M. testulalis in the terminal shoots was not significant at the 5% level of probability because of the very low infestation of this part of the plant. In the flowers and pods, Decis® was better than Systoate® which failed in controlling this borer satisfactorily. In the unsprayed plots (i.e. control), the peak of the natural infestation occurred in the flowers towards 50 DAP and 65% of the flowers were injured. In the pods, up to 89% of infestation by M. testulalis larvae were observed 60 DAP. The lowest yield was recorded from the unprotected plots (322 kg/ha) whereas the treatment 0-Decis®Systoate®Decis® provided the highest yield (1367 kg/ha) and the highest returns.

The temporal evolution of the populations of Megalurothrips (=Taeniothrips) sjostedti (Trybom) (Thysanoptera, Thripidae) (larvae and adults) and of Maruca testulalis (Geyer) (Lepidoptera, Pyralidae) (larvae) as well as the rate of flower infestation by these insects was carried out under Held conditions using 10 cowpea varieties (IT 82D-889, IT 82D-287, IT 82D-716, IT 82D-789, IT 82D-703, IT 82D-713, IT 82D-890, IT 82D-709, TVu 57 and “Kpodjiguegue”).

The investigation was carried out during the 1984 early cropping season (from April to July) at Abomey-Calavi. In the research station the abundance of M. sjostedti populations was observed 47 days after planting (DAP) for one variety and 68 DAP for the nine other varieties (384–634 thrips/20 flowers according to the varieties). In addition, the decline of the insect population was recorded 40 DAP for four varieties and 75 DAP for the six other varieties (88–375 thrips per 20 flowers according to the varieties). But 90–100% of the sampled flowers were infested by M. sjostedti towards 40 DAP whereas 95–100% of flowers were injured 68 DAP.

Larval populations of M. testulalis reached their maximum value 40 DAP for four varieties and 47 DAP for the six other varieties (4–17 larvae/20 flowers according to the varieties). The population declined 61 DAP for two varieties, 68 DAP for seven varieties and 75 DAP for one variety (0–3 larvae/20 flowers according to the varieties). Regarding the rate of flower infestation by M. testulalis, the highest percentages (20–70% according to the varieties) were obtained among all varieties from the same sampling dates where the larval population peak was noted for the same varieties. In the same way, lowest percentages (0–15% according to the varieties) were recorded among all varieties on the same dates where the minimum value of larval populations of the pest was obtained.

M. sjostedti and M. testulalis fluctuate in opposed phase. The peak value of M. sjostedti generally coincides with the minimum value of M. testulalis and inversely. But the peak activity period of both insects occurs between 40 and 70 DAP. The average number of insects recorded all along the sampling period has shown significant differences (P=0.05) between the various cowpea varieties for M. sjostedti and M. testulalis. The biological and nutritional factors that contribute to such population fluctuations are discussed in the light of results obtained.

In a screen cage study, the pattern of flower and pod development at the various flowering nodes of three cowpea varieties with known susceptibility to the pod-borer Maruca testulalis, was mapped out. The period of flower opening over the whole plant spanned an average of 13 days in TVu946, 17 days in ICV-2 and 18 days in Vita-1 with 85–100° of the pods retained to maturity coming from flowers opening within 8 days of anthesis. The efficiency of pod production from open flowers was highest in TVu 946 (54°), lowest in Vita-1 (11°) and median in ICV-2 (31°). However, as a consequence of the individual pod size, the overall pod and seed characteristics in decreasing order were Vita-1, ICV-2 and TVu 946. The bulk of flowers and pods on the plants were produced at the basal plant nodes where primary branches were developed.

Pod elongation and enlargement were initially rapid in all varieties, but the TVu 946 pods reached physiological maturity 2 days before the other two varieties. The eventual pod size and rate of pod growth appear to be important factors in the susceptibility of cowpea to the pod-borer attack.

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.

The structure of hildecarpin, an insect antifeedant 6a-hydroxypterocarpan isolated from the roots of Tephrosia hildebrandtii has been confirmed by a combination of degradation reactions, NMR and mass spectra. Hildecarpin has been dehydrated to the corresponding pterocarpene 3-hydroxy-2-methoxy-8,9-methylenedioxypterocarpene. Hydrogenation and hydrogenolysis of the pterocarpene has afforded the isoflavan 2′, 7-dihydroxy-6-methoxy-4′,5′-methylenedioxyisoflavan, acetylation of which has led to 2′, 7-diacet6xy-6-methoxy-4′,5′-methylenedioxyisoflavan. The NMR and mass spectra of the degradation products confirm the structure previously assigned to hildecarpin.