Laboratory and screenhouse experiments were conducted to identify antibiosis and tolerance in four wild accessions of cowpea, Vigna unguiculata subsp. dekindtiana, to Clavigralla tomentosicollis Stål, the most damaging pod-sucking bug on cultivated Vigna genotypes in West Africa. The wild accession TVnu 151 showed antibiosis resistance, causing >50% mortality of the nymphs within 3 d of placing them on pods. Nymphs died more quickly on TVnu 151 than on TVnu 72, the wild and resistant control of the V. vexillata species which affected the weights of surviving insects to a much greater degree than TVnu 151. The three other accessions of the subspecies dekindtiana (TVnu 369, TVnu 517, and TVnu 707) did not cause significant mortality to the bugs, but rather extended their developmental time, with surviving adults showing lower weights and slower oviposition rates than those on the susceptible control IT84S-2246. Wild accessions affected male and female bugs differently, resulting in differential survival. This was reflected by the sex ratio which was male biased on the wild accessions (1:0.3-1:0.9), and female biased on IT84S-2246 (1:1.5). No evidence of tolerance was found in the four accessions of V. unguiculata subsp. dekindtiana. Overall, seed traits seemed to be the major resistance component in these wild accessions.

Several Vigna species were used to determine the role of pod trichomes and pod toughness in the resistance of cowpea to feeding damage by the coreid bug Clavigralla tomentosicollis Stal. The scanning electron microscopy study revealed the presence of glandular and non-glandular trichomes on the pod wall of all test genotypes. The cultivated genotypes TVu 1890, TVu 3354 and IT84S-2246 of the V. unguiculata ssp. unguiculata showed significantly lower (P<0.05) densities of glandular trichomes than accessions of the wild Vigna species (TVnu 72, TVnu 151, and TVnu 707). All pods were similar with respect to the density and length of non-glandular trichomes. The two wild accessions TVnu 151 and TVnu 707 of the V. unguiculata ssp. dekindtiana had low pod strength similar to that of the susceptible genotype IT84S-2246, and also showed high seed damage levels comparable to that of this susceptible genotype. These accessions of the subspecies dekindtiana contrasted with the wild and resistant accession TVnu 72 of the V. vexillata species which suffered minor seed damage in

A comparative account is given of the rate of infestation of seedlings of Triplochiton scleroxylon Schum. by Diclidophlebia sp. under three regimes of ‘shade’. Population increase in relation to leaf production under the different regimes, and insect activity in ‘Deep shade’ is also discussed. Shade decreased the rate of infestation of the host plant and the build‐up of populations of the insect. Under ‘Deep shade’ practically no infestation occurred, probably because the adult insects were less active there. Shading is recommended as a method of silvicultural control of this pest in nursery and transplant beds. Résumé EFFET DE L'OMBRE SUR LE TAUX D'INFESTATION DE TRIPLOCHITON SCLEROXYLON PAR LE PSYLLE DICLIDOPHLEBIA SP. On a étudié l'influence de l'ombre sur le taux d'infestation d'une plante (Triplochiton scleroxylon) par un Psylle, Diclidophlebia sp. en utilisant trois degrés différents d'éclairement, correspondant à ce qu'on a nommé «ombre foncée» «ombre claire» et «ombre nulle». L'éclairement et la température ont été mesurées et chacune des expériences a été répétée quatre fois. On a enregistré chaque semaine: (a) le nombre total de feuilles (b) le nombre de feuilles infestées et (c) le nombre de psylles adultes présents sur les jeunes plantes. Une rectification a été faite pour les feuilles endommagées par d'autres espèces d'insectes. On a donc calculé le pourcentage de feuilles infestées par des larves et le nombre des insectes adultes pour cent feuilles. On a trouvé une différence significative du taux d'infestation, entre les trois expériences correspondant à des éclairements variés. On a observé que l'ombre diminue l'intensité des attaques de Diclidophlebia sp. sur sa plante‐hôte. Le taux d'infestation des feuilles et l'ensemble de la population d'insectes furent fort réduits chez les plantes soumises aux régimes d'éclairement «ombre foncée» et «ombre claire». Il n'y avait pratiquement pas d'infestation des plantes en «ombre foncée». La rareté des insectes dans ce cas fut considérée en rapport avec (1) le taux de protéines et/ou des hydrates de carbone dans les feuilles des jeunes plantes qui sont ombragées et (2) l'incidence d'un éclairement réduit du type «ombre foncée». On a conclu que l'élément le plus important est le niveau bas de l'éclairement dû à l'ombrage, qui réduit l'activité des insectes adultes. L'ombrage ayant peu d'influence sur la croissance des jeunes plantes de Triplochiton scleroxylon, on a recommandé ce moyen pour protéger semis et pépinières contre les attaques de Diclidophlebia.

Diclidophlebia eastopiVondracek and D. harrisoni Osisanya are pests of the timber tree Triplochiton scleroxylon in Nigeria. The egg and five nymphal instars are described and illustrated. Under laboratory conditions the life-cycle (egg-egg) of D. eastopi was completed in 18-J-days, and mated fed females had a life span of IS days. The sex ratio in the field was 1:1. Nymphs feed near the veins of mature leaves, causing premature leaf fall; adults feed on leaves of any age and cause no symptoms. Fecundity averaged 502 eggs, with a daily oviposition rate of 38; most eggs are laid in batches along the veins of mature leaves. The life-cycle of D. harrisoni was 16 days; mated and fed females lived 10 days. The feeding of firstinstar nymphs near the margins of young leaves causes leaf tunnels to form, inside which the nymphs complete their development; adults feed only from young leaves. In the field the female:male ratio was 2:3. Fecundity averaged 131, with a daily oviposition rate of 31. Fertility improved with multiple matings. The eggs are laid singly, partially embedded in the epidermis, and only on young leaves.

The effects of secondary metabolites in different Vigna species on the development of Clavigralla tomentosicollis were investigated in an artificial seed system using different fractions of crude pod extracts, while the orientation response of this pod‐bug to volatile extracts was studied using a dual‐choice olfactometer. Feeding on the neutral fraction extracts, in contrast to the basic and acidic fractions, resulted in significantly higher mortalities, longer total developmental time, and lower growth index of the insects in comparison with controls. All volatile extracts elicited an avoidance reaction by C. tomentosicollis, except the volatile from the susceptible genotype IT84S‐2246 which generally attracted as many insects as controls. Extracts from wild Vigna species showed higher activity than those from their cultivated relatives. The present study which has established that most secondary metabolites in cowpea pods were localized in the neutral fraction of the crude extract, could facilitate experiments on the separation and characterization of the toxic factors involved.