Natural enemy activity following the introduction of Epidinocarsis lopezi (Hymenoptera: encyrtidae) against the cassava mealybug, Phenacoccus manihoti (Homoptera: psudococcidae), in southwestern Nigeria

Published online: 15 September 2014The effectiveness of the exotic South American hymenopterous parasitoid Epidinocarsis lopezi (De Santis) in controlling the cassava mealybug (CM), Phenacoccus manihoti Matile-Ferrero, in southwestern Nigeria, was assessed using emergence samples. Ten infested cassava tips were collected from each of 679 fields during four surveys over an area of 200,000 km2 in the 2 yr following establishment of the parasitoid. These samples were used to determine frequency and abundance of this and other insects associated with the CM. Survey results suggest that CM infestation levels as measured by frequency of plants showing CM damage symptoms declined as a result of the parasitoid's activity from 88% at the end of the first dry season (March 1983) to 23% in the same period the following year. E. lopezi numbers per field also declined during the same period, but parasitoid densities per infested cassava tip in both years remained the same. A sharp fall in numbers of indigenous polyphagous coccinellids on cassava, particularly of Hyperaspis spp. and to a lesser extent of Exochomus sp., was also associated with decline in CM infestation levels. By contrast, the infested tip densities of the cecidomyiid Dicrodiplosis manihoti Harris, which is specific on CM, were not affected. Other indigenous primary parasitoids of the genus Anagyrus were rare. Ten species of native hyperparasitoids were common from E. lopezi; most common were Prochiloneurus spp. and Chartocerus spp. As E. lopezi densities declined, percent hyperparasitism dropped significantly from 43.8% in March 1983 to 30.7% in March 1984, and from 35.7% in December 1983 to 17.5% in December 1984. In the last two surveys, CM densities, as determined from dissected cassava tips, were low throughout southwestern Nigeria. It is concluded that E. lopezi is responsible for declines in CM densities and damage symptoms, for reduction of coccinellid abundance via competition for a common food source, and that hyperparasitism does not prevent E. lopezi from being an efficient parasitoid

Sustained biological control of the cassava mealybug Phenacoccus manihoti (Hom: Pseudococcidae) by Epidinocarsis lopezi (Hym.: Encyrtidae) in Nigeria

Following the successful introduction of Epidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM) Phenacoccus .manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids, demonstrating the long-term success of biological control by E. lopezi in the region. Indigenous polyphagous coccineilids were found only during peak host densities, whereas the specific E. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89 % of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated for individual infested tips (N = 4,878). Parasitism increased slightly with host density on tips having between I and 10 CM of the 3 rd and 4 th instars, indicating positive density dependence. Such tips comprised 64 % of all infested tips. At higher host densities, parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological control agents

Impact of the exotic parasitoid Epidinocarsis lopezi on cassava mealybug (Phenacoccus manihoti) populations

Published online: 01 Dec 1987Epidinocarsis lopezi an exotic parasitoid to Africa, was first released to control the cassava mealybug (CM), Phenacoccus manihoti, at IITA (Ibadan) in November 1981, and a year later at Abeokuta, both in southwestern Nigeria. Population dynamics study of CM and its natural enemies was conducted for 4 years. CM population peaks usually occurred during the second half of the dry season (January-April). E. lopezi was the only natural enemy that was found during the whole year and in high densities. Parasitization rates of E. lopezi alternated with CM densities, thus suggesting a regulatory effect on CM populations by this parasitoid. CM populations were drastically reduced in release fields when compared with control fields. Subsequently CM populations have been maintained below injury levels for 4 years. E. lopezi is considered an efficient parasitoid of the CM

Lutte biologique contre la cochenille du manioc (Phenacoccus manihoti) avec le parasitoïde exotique, Epidinocarsis lopezi

Dans IDL-1152

Changes in the composition of the fauna associated with the cassava mealybug, Phenacoccus manihoti, following the introduction of the parasitoid Epidinocarsis lopezi

Published online: 01 Dec 1987Over 130 species of insects were found in association with the cassava mealybug (CM), Phenacoccus manihoti, and its newly introduced parasitoid Epidinocarsis lopezi in Africa. As the CM in SW Nigeria declined under the influence of E. lopezi, this introduced wasp maintained densities of 2.8-3 per CM-infested tip early in the dry season and 1.3-1.6 per infested tip late in the dry season, but declined overall from 1.3 to 0.2 per randomly collected tip within 1 year. The decline of CM led to a sharp reduction in numbers of indigenous coccinellids, particularly of Hyperaspis spp. and to a lesser extent of Exochomus sp., due to competition with E. lopezi for the common food source. Numerous species of other polyphagous predators and parasitoids of coccinellids were found in low numbers. Indigenous primary parasitoids, Anagyrus spp., were rare, but their 10 spp. of hyperparasitoids were often reared from E. lopezi, with Prochiloneurus spp. and Chartocerus spp. being the most common. Hyperparasitism declined from 41.3% in March 1983 to 16.9% in Dec 1984 and proved to be positively density-dependent. The effects of hyperparasitoids on this biological control programme are discussed

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

Published online: 27 Jun 2003In 1981 the South American parasitoid Epidinocarsis lopezi (DeSantis) was imported into Nigeria for control of the cassava mealybug, Phenacoccus manihoti Mat.-Ferr. It was multiplied in an insectary at the International Institute of Tropical Agriculture (IITA), Ibadan, and first released in 1981/82. Within 3 years it dispersed over 200 000 km2 in southwestern Nigeria, occupying between 70 and 98% of all fields. By December 1985, a total of over 50 releases in 34 regions had been made in 12 African countries. E. lopezi was already established in 28 regions, and in some cases E. lopezi spread across international borders. It now occupies 650 000 km2 in 13 countries: 420 000 km2 in West Africa, 210 000 km2 in Central Africa and several small disjunct territories, covering a range of ecological zones (Sudan Savannah, Guinea Savannah, Equatorial Rainforest, Highlands)

The role of kairomones in prey finding by Diomus sp. and Exochomus sp. two coccinellid predators of the cassava mealybug, Phenacoccus manihoti.

We studied searching behaviour of Diomus sp., a coccinellid predator introduced into Africa as a natural enemy of the cassava mealybug, when searching on cassava leaves, and compared its behaviour with the searching behaviour of Exochomus sp., an African predator of mealybugs (MB's). Female adults of Diomus and Exochomus spent more lime searching on cassava leaves previously infested with cassava MB than on clean cassava leaves, in response to substances produced by MB's (wax and/or honeydew) still present on these leaves as kairomones after removal of the MB's. Both species were also arrested by wax and/or honeydew of the citrus mealybug, Planococcus citri. When offered a choice between kairomones of both MB species only experienced Diomus (reared on cassava MB) showed a clear preference for kairomone of cassava MB. Separate influences of wax and honeydew were tested. Wax from cassava MB was an arrestment stimulus for both coccinellid species. Honeydew produced by cassava MB arrested Exochomus and inexperienced Diomus

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

1. In cassava fields in Africa, population sex ratios of Epidinocarsis fopezi vaned from 0.44 (males to total parasitoids) at low host densities to highly male-biased ratios of 0.70 at high host densities. 2. This variability is caused by the difference in allocation of sons and daughters to hosts of different sizes, through the following mechanisms: (a) small, i.e. second instar, hosts are mainly used for the production of male offspring, whereas in large, i.e. third instar, hosts a variable, female-biased sex ratio is produced; (b) E.fopezi does not selectively oviposit into large hosts but always accepts both small and large hosts for oviposition upon encountering; (c) in the field, this parasitoid is time-limited, and not egg-limited. On the basis of an optimal diet model, such general host acceptance is shown to be the best strategy. 3. Thus, sex ratio increases with host density for three reasons: the proportion of small hosts encountered in the field increases with increasing host density, small hosts are used for male production, and hosts are always accepted when encountered