P. Neuenschwander

Economic impact of biological control of water hyacinth in Southern Benin

Abstract A biological control program of water hyacinth was undertaken in Southern Benin between 1991 and 1993. It consisted of the release of three natural enemies, two weevil species and one moth, that feed exclusively on water hyacinth. In 1999, a survey of 365 men and women from 192 households in 24 villages in the target area, using participatory and quantitative methods, revealed that water hyacinth, although not eliminated, was perceived by the villagers as having been reduced from a serious pest to one of minor or moderate importance. According to their estimates of the impacts they perceived, at the peak of the infestation water hyacinth had reduced the yearly income of this population of about 200 000 by approximately US

Interference by ants in biological control of the cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae) in Ghana.

84 million. Lost revenues for men were mostly in fishing, while women experienced lost revenues in trade, primarily food crops and fish. The reduction of water hyacinth cover through biological control was credited with an increase in income of US

Socio-economic impact of biological control of mango mealybug in Benin

30.5 million per year. The total cost of the control program is estimated at a present value of US

Introduction and dispersal of Epidinocarsis lopezi (Hym., Encyrtidae), an exotic parasitoid of the cassava mealybug, Phenacoccus manihoti (Hom., Pseudococcidae), in Africa

2.09 million. Assuming the benefits are to stay constant over the next 20 years, a most conservative assumption, the accumulated present value would be US

Factors affecting biological control of cassava mealybug by exotic parasitoids: a ratio-dependent supply-demand driven model

260 million, yielding a respectable benefit cost ratio of 124:1. This ratio is calculated for direct economic effects on the people of Southern Benin only, and does not take into account indirect benefits or the benefits of the project to other countries were the biological control agents were successfully introduced. Other effects mentioned, but not measured, included an increase of water quality and of human health.

Biological control of the cassava mealybug, Phenacoccus manihoti (Hom., Pseudococcidae) by Epidinocarsis lopezi (Hym., Encyrtidae) in West Africa, as influenced by climate and soil

In surveys of cassava fields in the coastal savanna and rain forest zones of Ghana, eight species of ants, mostly in the genera Camponotus, Crematogaster and Pheidole (Hymenoptera: Formicidae), were found attending cassava mealybug, Phenacoccus manihoti Matile-Ferrero. Ant densities were much higher in the rain forest than in the savanna and, in most zones, positively correlated to mealybug population densities. Pheidole megacephala (Fabricius) was the only species more abundant in the interior of fields, whereas the other species preferred the edges of fields or, like Camponotus spp., did not respond to edge effects. Weediness of the fields did not clearly influence the presence of ants. Crematogaster sp. and P. megacephala spent most of the time on cassava tips, where they built carton tents. Ants of the three genera reduced parasitism rates by the exotic Epidinocarsis lopezi (De Santis) (Hymenoptera: Encyrtidae) to half, compared to the rates observed on mealybug colonies of equal size that were not attended. Hyperparasitism by Prochiloneurus insolitus (Alam) (Hymenoptera: Encyrtidae) and Chartocerus hyalipennis Hayat (Hymenoptera: Signiphoridae) and predation by the indigenous Exochomus troberti Mulsant (Coleoptera: Coccinellidae) were similarly reduced. Where ants were excluded experimentally by insectcide barriers, parasitism was 32%, compared to only 10% in the control, and predator densities were reduced three-fold. In a 24 h experiment, Pheidole megacephala was observed to remove about half the E. troberti larvae; Crematogaster sp. and Camponotus spp. were less efficient. The results show the locally strong interference of ants with biological control of the cassava mealybug. Despite this interference, mealybug populations in the rain forest were judged to be below damaging levels.

Evaluating the efficacy of biological control of three exotic homopteran pests in tropical Africa.

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

Sex ratios in field populations of Epidinocarsis lopezi, an exotic parasitoid of the cassava mealybug, in Africa

328 per year by the biological control programme. Extrapolated to all producers of Benin, a yearly gain of US

Competition between Gyranusoidea tebygi and Anagyrus mangicola, parasitoids of the mango mealybug, Rastrococcus invadens: interspecific host discrimination and larval competition

50 million in mango production can be estimated. The present value of accrued benefits is estimated at US

Biological Control of Tropical Weeds Using Arthropods: Pistia stratiotes L. (Araceae)

531 million over a period of 20 years. The total cost of the biological control of mango mealybug is estimated at US