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 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.

Insect pests are major constraints in cowpea production. Breeding for insect resistance is a major objective of cowpea improvement programme at IITA. Resistance to leafhoppers and aphids has been incorporated in advanced breeding lines thus eliminating the need for other control measures. Similarly, a moderate level of resistance to thrips and cowpea storage weevil has also been incorporated thus reducing the damage due to these two pests. A moderate level of resistance to legume pod-borer and pod sucking bugs has also been identified and is being incorporated in advanced breeding lines. The long term strategy is to develop cowpea cultivars with multiple resistance to insect and diseases with superior agronomic characters and local adaptability.

The studies show that the population of Maruca testulalis fluctuates greatly between the long and short rainy season and is significantly lower during the short and dry season, even when the cowpea crop is maintained under irrigation conditions. Studies on larval and pupal populations at Mbita Point, in Western Kenya and related farmers' plots showed lower populations under pure cowpea than under cowpea-maize intercrop, especially at 50% cowpea flowering stage (i.e. the second sampling stage). Although this difference was consistently manifested in the three seasons of experimentation there was no significant difference in larval population and extent of flower damage. Studies using three susceptible cowpea varieties (Ex-Lwanda, TVX 66-2H, and TVX 1193-059D) showed no significant difference in larval, pupal and adult populations when unsprayed. However, when sprayed with dimethoate (Rogor E 40) a systemic insecticide, significantly higher larval population was obtained in TVX 1193-059D, which shows the most vegetative growth of the three varieties. The borer damage on the flowers was not significantly different in all varieties under both the sprayed and unsprayed conditions. Studies using assessment of the different larval instars of M. testulalis in both sprayed and unsprayed conditions showed a continuous infestation of the crop throughout the season unless pod and flower production ceased. The fourth and fifth instar larvae were more abundant in pods than in flowers of the cowpea plant.

A model for mass-rearing of tropical crop-borers has been developed using Maruca testulalis as a case study. Maruca testulalis (Geyer) (Lepidoptera: Pyralidae) has been reared from egg to adult for three generations on artificial diet at laboratory room temperature ranging between 25−30°C with a 12-hr photoperiod. The total life cycle was completed in 23 days. Average life data from the three generations reared on diet are larval period (13.35 days), pupal period (6.67 days); pupal weight (52.69 mg) for female and (49.68 mg) for male; survival to adult 60.3%; fecundity (257.1) eggs per female.

The development of a mass-rearing technique of Mantea testulalis by the ICIPE has allowed us to start extensive work on cowpea resistance to the legume pod-borer. A preliminary field observation showed that the cowpea resistance is on the low level. Therefore, our effort initially concentrated on the development of new methods and techniques which were sufficiently sensitive to separate lines possessing small differences of resistance. Eight different treatments were used to develop the methodology of cowpea screening under artificial infestation with Maruca larvae and eggs in the screenhouses and seven treatments in the field.

Plant growing stage has modified the expression of cowpea resistance to Maruca larvae. Five-seven shoots stage (not younger) was found to be most suitable for screening for resistance in pre-flowering period. By using five eggs/plant in pre-flowering stage on cowpea plants grown on the ground, it was possible to differentiate between the resistant and susceptible lines. The standard error between plants treated with 10 eggs/plant treatment was lower than those with five eggs/plant treatment. Therefore, if laboratory colony allows the higher infestation of 10 eggs/plant, it is recommended. Using 10 or 20 eggs/plant in flowering stage correctly segregated cowpea lines for resistance and susceptibility based on larval survival and damage level of flower buds, flowers and pods.

Preliminary studies on the population of the legume pod-borer Maruca testulalis Geyer, using a pheromone trap at Mbita Point on the shores of Lake Victoria, showed that female moths produce a pheromone which attracts males. It was found that the peak catch of males occurred on the third night of female emergence, but after the fifth night the females were not attractive to males. This finding is regarded as significant in terms of studies on the population dynamics of M. testulalis.

A procedure has been developed which allows production of 75,000 eggs per month of the legume pod-borer, Maruca testulalis (Geyer). More than 170 eggs per moth were obtained. The optimal number of moths placed in the mass oviposition cage having potted cowpea plants was 30. The average life-span of the moths was 7.7 and 9.5 days for females and males, respectively. The optimal number of larvae in the rearing box was 50: larval survival declined sharply above a density of 50 per box.

Preliminary studies on the life history and behaviour of the legume podborer, Maruca testulalis (Geyer), at Mbita Point on the shores of Lake Victoria have shown that most of the eggs (86%) of M. testulalis are laid on the leaf. Over 90% of such eggs laid on the leaf are oviposited on the lower leaf surface. Most adults were found to emerge between 2000 and 2300 hr. The number of eggs laid per female varied between 6 and 194, and over 72% of these were fertile. No larval or pupal diapause was observed.

Larval duration was 8–14 days and the pre-pupal stage lasted only 12–24 hr. The whole life cycle at Mbita Point was found to be about 20–57 days.

An important factor that previously discouraged detailed studies on the biology of M. testulalis is the fact that the eggs are translucent and extremely difficult to see against the background of the oviposition site. The discovery of these eggs was a major step in beginning to work on this important pest.