PAPER SESSION III: BIOLOGY AND DIVERSITY OF THE ACARI

CHAIRPERSON: Prof. P.D. Theron

PAPER 10

Dietary influence on life history and predation of the phytoseiid mite, Amblyseius zaheri (Acarina: Phytoseiidae)

A.H. Rasmy, F.M. Momen & G.M. Abou-Elella

National Research Centre, Dokki, Cairo, Egypt, E-mail: aly_rasmy@hotmail.com

Laboratory experiments were conducted to study the biology and predation capacity of the phytoseiid mite Amblyseius zaheri Yousef & El-Borolessy as affected by feeding on different diets. The predatory mite was able to develop and reproduce when fed on nymphs of the two-spotted spider mite Tetranychus urticae Koch, nymphs of the citrus brown mite Eutetranychus orientalis Klein, motile stages of the eriophyid mite Eriophyes dioscoridis Soliman & Abou-Awad, eggs of the scale insect Parlatoria ziziphus Lucas, nymphs of the white fly Bemisia tabaci (Genn.) and pollen grains of date palm. The present study revealed that the type of food significantly affected development, female longevity, sex ratio, fecundity and predation capacity of A. zaheri.

PAPER 11

Within-plant distribution of tetranychid mites (Tetranychus sp.) on tomato plants (Lycopersicon esculentum Mill).

I. Sarr¹, M. Knapp¹, J. Baumgärtner¹, C.P.K.O. Ogol²

¹International Centre of Insect Physiology and Ecology (ICIPE), P.O. Box 30772, Nairobi, Kenya, E-mail: isarr@icipe.org

² Kenyatta University, Department of Zoology, P.O. Box 43844, Nairobi, Kenya

The within-plant distribution of the different stages of tetranychid mites on tomato was investigated in field conditions at Kibwezi, Kenya. There was a significant difference (p≤0.05) between the subpopulations of mites (eggs, immatures, females and males) found in the different canopy layers. However, there was no significant difference between the mites density on different parts of the leaves (the three terminal leaflets and the rest of the leaf) except for the eggs whose density was higher on the three terminal leaflets. All the mite life stages showed within plant aggregative patterns and were more abundant on the lower part of the tomato canopy throughout the growing season in field conditions with up to 43% of the mite population per plant. 34% and 23% of the mite population per plant colonised the uppermost and the medium parts respectively. This study suggests the leaves located in the basal shoot of tomatoes as the optimal sampling zone for tetranychid mites.

PAPER 12

Do generalist phytoseiid mites have interactions with their host plants?

S. Kreiter, M.-S. Tixier & T. Bourgeois

Ecole Nationale Supérieure Agronomique de Montpellier (ENSA-M)/Institut National de la Recherche Agronomique (INRA), Animal Ecology & Agricultural Zoology Unit, Laboratory of Acarology, 2 Place Pierre Viala, 34060 Montpellier cedex 01, France. E-mail: kreiter@ensam.inra.fr, garcin@ensam.inra.fr

In order to study factors affecting phytoseiid mite occurrence in uncultivated areas, we sampled phytoseiid mites (densities, diversity and age structure) on several plants located in 4 uncultivated areas surrounding vineyards over 3 years to determine how plants and mainly their leaf structure affect mite communities. The plant composition of these areas greatly influenced phytoseiids density and diversity. The relationships between leaf structure (trichomes, pollen densities, number and structure of domatia, leaf surface) and Kampimodromus aberrans (Oudemans) densities were also studied. The frequency of occurrence and the abundance of K. aberrans per cm² were correlated to high trichome densities. A complex phylloplane (many hairs and shelters or domatia) could confer a competitive advantage to K. aberrans over other phytoseiid mite species. The number and the rating of domatia were important to K. aberrans development; high proportions of immatures were observed only on plants with these structures. Pollen densities were significantly correlated to trichome densities; domatia structure had only a somewhat lesser effect. Furthermore, we demonstrated that K. aberrans does take up plant fluids. Our study shows how dense trichome and pollen levels could affect the development of K. aberrans populations and add perspective on the influence of domatia on this important predaceous mite populations.

PAPER 13

Native phytoseiid fauna in cassava agro-ecosystems in southern Africa before and after the introduction of exotic phytoseiids

I. Zannou¹, R. Hanna¹, G. de Moraes², & S. Kreiter³

¹Biological Control Centre for Africa, International Institute of Tropical Agriculture (IITA), 08 BP 0932, Cotonou, Benin, E-mail: i.zannou@cgiar.org

²Depto. Entomol., Fitopatol. e Zool. Agrícola, ESALQ- Univ. São Paulo, Piracicaba-SP, Brazil

³Ecole Nationale Supérieure Agronomique de Montpellier, Montpellier, France.

The cassava green mite Mononychellus tanajoa (Bondar), an introduced pest of cassava in Africa, has been the target of a major classical biological control campaign by the International Institute of Tropical Agriculture (IITA). After numerous introduction attempts, three predatory mite species of the family Phytoseiidae were established in several countries, but only Typhlodromalus aripo has shown the ability to readily establish and quickly spread on a continental scale. In an effort to determine the impact of T. aripo introduction on native phytoseiids, detailed food web surveys were conducted before and after its introduction in southern Africa (Malawi and Mozambique). Two pre-introduction surveys were conducted in each of the two countries- June 1999 and April 2000 in Mozambique, and July 1999 and May 2000 in Malawi; and one post-introduction survey was conducted in each country- April 2001 and May 2001 in Mozambique and Malawi, respectively. In each of the surveys, all phytoseiids were collected from the apex and from one leaf from each of the top, middle and bottom strata of each of 30 randomly selected cassava plants per field; and from the five most common associated plant species in each field. In addition to cassava, more than 100 associated plants were sampled in both surveys during which more than 40 phytoseiid species were collected. Species composition differed substantially between the two countries. In Mozambique, Euseius baetae, Euseius bwende and Typhlodromalus saltus were the dominant phytoseiid species on cassava, whereas E. baetae, Amblyseius sundi and Paraphytoseius horrifer were the common species on associated plants. In contrast, Iphiseius degenerans, Euseius fustis and T. saltus were the common species on cassava, while, I. degenerans, Euseius magucii and Euseius dossei were the dominant species on associated plants in Malawi. With only one year of post-introduction data, no significant differences were found in the abundance and species composition of common phytoseiid species recorded on cassava prior and after the introduction of T. aripo.