No abstract

Rastrococcus invadensWilliams has been the most important polyphagous pest of horticultural crops since 1982 in some West African countries. It originated in South-East Asia and was probably introduced on infested plant material. The pest has been reported up to 150 km north of the coast of Benin and 500 km north from the coast in Togo. Although the species is polyphagous, mango, citrus, breadfruit, banana, frangipani (Plumeria alba) and species of Ficus are among the most attacked hosts. Several indigenous natural enemies were identified, but their ability to regulate the populations of R. invadens is very low. The most important among the predators were the coccinellids Chilocorus nigrita (F.), Exochomus promtus Weise and E. troberti Mulsant and the lycaenids Spalgis spp. In Togo, an indigenous parasitoid, Anagyrus sp. ?nr aurantifrons Compere, has become adapted to the pest.

Twenty-five villages of Northern Benin were surveyed to identify the constraints of yam chips production, assess the diversity of storage insects on yam chips, and document farmers' perception of their impacts on the stocks and their traditional management practices. Damages due to storage insects (63.9% of responses) and insufficiency of insect-resistant varieties (16.7% of responses) were the major constraints of yam chips production. Twelve insect pest species were identified among which Dinoderus porcellus Lesne (Coleoptera, Bostrichidae) was by far the most important and the most distributed (97.44% of the samples). Three predators (Teretrius nigrescens Lewis, Xylocoris flavipes Reuter, and Alloeocranum biannulipes Montrouzier & Signoret) and one parasitoid (Dinarmus basalis Rondani) all Coleoptera, Bostrichidae were also identified. The most important traditional practices used to control or prevent insect attack in yam chips were documented and the producers' preference criteria for yam cultivars used to produce chips were identified and prioritized. To further promote the production of yam chips, diversification of insect-resistant yam varieties, conception, and use of health-protective natural insecticides and popularization of modern storage structures were proposed.

The biology of Epidinocarsis (=Apoanagyrus) lopezi (DeSantis) was studied under fluctuating laboratory conditions of 24 -3 I~ and 79 -90 96 R.H. It is a solitary internal parasite. There are 4 tailed larval instars. The total developmental time from egg to adult ranged from 11 -25 days, average 18 days. The duration of each developmental stage was : egg 2 days, 1st instar 1 day, 2nd instar 1 day, 3rd instar 2 days, 4th instar 2 days, prepupa 4 days and pupa 6 days. Males mated several times, females mated once. Mated females produced both males and females, unmated females produced only males. Mated ovipositing females lived for 13 days while non-ovipositing mated females lived for 25 days. Parasitization decreased with increasing host density from 30 % at a density of 10 hosts/plant/female to 11% at a density of 50. There was virtually no pre-oviposition period. Based on 10 females, the highest mean daffy progeny production was 10. Females have an average oviposition period of 11 days and an average of 67 aduIt progeny. The sex-ratio was 1:2.3 in favour of females.KEY-WORDS : Life-cycle, fecundity, sex-ratio, numerical response to host density, hyperparasitism.Epidinocarsis ( = Apoanagyrus) lopezi (DeSantis) a parasite of cassava mealbug Phenacoccus manihoti Matile-Ferrero., is native to South America. It was introduced into Nigeria by the International Institute of Tropical Agriculture (IITA) for the biological control of the cassava mealybug CMB. It has been released in 2 locations ; one at the IITA experimental field in Ibadan, Oyo State in 1981 and the other in a 3,000 hectare cassava farm in Abeokuta, Ogun State in 1982. From these 2 locations the parasite was reported to have spread throughout Ogun, Oyo, Ondo, kagos and Kwara States covering an area extending from the rainforest into the Guinea Savanna (IITA, 1984). Its performance was apparently so impressive that plans are now on at IITA for a large scale mass rearing and air-release of miUions of this parasite in Nigeria and other African countries. However, our own assessment of the parasite differed.The present study was therefore concerned with basic laboratory investigations on the biology and morphology ofE. lopezi. It is hoped that the data will serve as the basis for subsequent biological and ecological investigations for proper field assessment of the effectiveness of the parasite.

Mango mealybug, an exotic pest of mango, was first observed in Benin in 1986. In a biological control programme, natural enemies were successfully released in the following years. The present study is the first attempt to measure the impact of the biological control of mango mealybug over a large area, through a survey of mango producers. Most producers attributed the observed improvement of mango production to the success of biological control. Based on production estimates by producers, the negative impact of the pest on plant production and the positive impact of the introduced natural enemy were demonstrated. Interviewed mango producers gained on average US$ 328 per year by the biological control programme. Extrapolated to all producers of Benin, a yearly gain of US$ 50 million in mango production can be estimated. The present value of accrued benefits is estimated at US$ 531 million over a period of 20 years. The total cost of the biological control of mango mealybug is estimated at US$ 3.66 million, which includes initial costs in other African countries and the introduction of the natural enemy from India, resulting in a benefit-cost ratio of 145:1 for benefits in Benin alone.