Effect of Predator Exclusion on Cassava Infested with Tetranychid Mites (Acari: Tetranychidae) A. R. BRAUN, A. C. BELLOTTI, J. M. GUERRERO, AND L. T. WILSON’ Cassava Program, Centro Internacional de Agricultura Tropical, Cali, Colombia Environ. Entomol. 18(4): 711- 714 (1989) ABSTRACT Chemical exclusion of predators with permethrin was used to test the effec- tiveness of the phytoseiid predator Amblyseius limonicus Garman and McGregor and a complex of minor predators in the biological control of tetranychid (Mononychellus spp., Tetranychus spp., and Oligonychus peruvianus McGregor) pests of cassava, Manihot es- culenta Crantz. Mononychellus spp. and Tetrunychus spp. populations were significantly higher and predator populations significantly lower in permethrin-treated plots than in control plots. Numbers of 0. peruviunus were not affected by permethrin. Yield of fresh commercial roots and of dry matter was significantly higher in plots with predators than in plots where permethrin was applied every 2 wk for predator exclusion. Yields of neither fresh nor dry matter in control plots were significantly different from yields in plots that had been protected with acaricide, suggesting that predation kept spider mite populations below economically damaging levels. KEY WORDS Arachnida, cassava, permethrin, predator exclusion CASSAVA, Manihot esculenta Crantz, is the most important starchy root crop in the tropics. Al- though considered to be relatively pest tolerant, recent research has shown that pests that are pres- ent throughout the growing cycle (e.g., spider mites) can depress cassava yield (Cock 1985). The tetranychid, Monon ychellus tanajoa (Bon- dar), was accidentally introduced to Africa from tropical America and has spread to 21 of the 34 African cassava-growing countries (IITA 1985).The absence of natural enemies is thought to be a major factor limiting the control of M. tanajoa in Africa. The objective of our study was to determine the effect of natural enemies in control Monony- chellus spp. and a related complex of tetranychids in their area of origin. One method of evaluating natural enemies is through the use of selective pesticides. Braun et al. (1987a) showed that permethrin could be used to eliminate Amblyseius limonicus Garman and McGregor, the most common phytoseiid predator in cassava in tropical America (Bellotti et al. 1987). The minor predators Oligota minuta Cameron (Coleoptera: Staphylinidae), Stethorus spp. (Co- leoptera: Coccinellidae), and spiders also are sus- ceptible to permethrin (Braun et al. 198713). Non- lethal side effects of permethrin in the cassava- tetranychid mite ecosystem such as phytostimu- lation and enhancement of phytophagous mite fe- Any opinions, findings, conclusions, or recommendations ex- pressed in this publication are those of the authors and do not necessarily reflect the views of the National Science Foundation. ‘ Department of Entomology, University of California, Davis, Calif. 95616. cundity were found to be of negligible importance (Braun et al. 198713). An advantage of selective pesticides over other techniques of predator exclusion, such as caging, is that they can be applied in large-scale field stud- ies, permitting the use of yield as a criterion for evaluating predator efficacy. Although yield data are generally reported in studies of biological con- trol with microbial agents, yield differences found in experiments with natural enemies of insects and mites are rarely published. Materials and Methods A predator-exclusion experiment was designed to measure the effect of mite predators on cassava mite abundance and on commercial fresh-root and dry-matter yield. Four cassava clones-MCol 22, CG5-79, ‘Montero,’ and ‘Venezo1ana’-were plant- ed at a density of 10,000 plants/ha in October 1984 on a farm in the arid northern coastal region of Colombia. The design was a split plot with four blocks, with clone as the main factor and pesticide treatment as the subplot factor. Each subplot con- tained 48 plants. The between-plot distance was 1 m. The pesticide treatments were permethrin ap- plication every 2 wk (6 g [AI]/100 liters Ambush 50; BASF, Federal Republic of Germany) for elim- ination of predators; acaricide treatment every 2 wk (Tedion V- 18; 2,000 g [AI]/100 liters tetradifon; N. V. Phillips Duphar, Amsterdam); and an un- sprayed control with natural populations of pred- ators and phytophagous mites. A gasoline-powered oO46-2%x/89 /0711-0714$02.oO/O Q 1989 Entomological Society of America This article is the copyright property of the Entomological Society of America and may not be used for any commercial or other private purpose without specific written permission of the Entomological Society of America.