progress in acarology

Reprint from

PROGRESS IN ACAROLOGY

Volume 2

Editors

G.P. CHANNABASA VANNA C.A. VIRAKTAMATH

1986 - VII Int'l . Congr. Ac a rology

OXFORD & IBH PUBLISHING CO. PVf. LTD. N ew D elhi Bombay Cal cutta

1988

9

PLANT MITES

Technical Reviewers SWARAJ GHAI A.G.A. SALMAN

9.1 AGRICULTURAL ACAROLOGY IN THE TROPICS-BASIC NEEDS 1 Carlos H. W. F/echtmann Department of Zoology, University of Sao Paulo, ESALQ; 13400 Piracicaba, Sao Paulo, Brazil

SYSTEMATICS

Whilst there are researchers in the field of systematics of plant mites in the tropics, some restrict themselves solely to the study of mites of a single crop. There is also pressure to give priority to the study of biology and, first of all, the control of the mite species of economic importanc~. Therefore, sound and stable systematics of plant mites in the tropics is needed, especially concerning the Tetranychidae ·and Eriophyidae, as well as the Tenuipalpidae and, to a lesser degree, the Tarsonemidae. I quote here the words of Gerson (1979) "The great worldwide proliferation of strains or races, especially in the genus Tetranychus (and in Mononychellus as was recently found to occur on cassavas in Africa and South America), some of which, although of common ancestry, do not interbreed, suggest that we may be witnessing an evolutionary process. One may postulate that acute selection pressure exerted by the wide use of pesticides as well as by the introduction , . of diverse new crops and sophisticated cultivation methods, is accelerating the process of ~ ~- speciation in Tetranychus, with special emphasis on the te/arius complex. This is very hard on the taxonomist, who is not only expected to provide names, but, must alsp designate type specimens and type localities:- But the biologist and extension worker are also confused: the 'species' they thought they understood last year is behaving in a rather different pattern this year." PLANT/MITE INTERRELATIONSHIPS

Plant responses to phytophagous mites are quite different between annuals and perennials. Plants with continuous vegetative growth probably react to mite feeding in a way different from perennials, which have a limited growing season. Assessment of the economic level of damage caused by plant-feeding mites to perennial and semiperennial plants is urgently needed. This would include studies that provide answers to questions like: How many mites per leaf can the plant tolerate before production is affected? How many leaves (or how much foliar area) can a plant lose before its production is reduced? Our rather deficient understanding of these plant-mite interrelationships lead to overemphasized applications of chemicals, mainly in annual crops. In semipere~nial and perennial crops the situation is identical, and progress on biological control based mainly on the rearing and releasing of Phytoseiida~, and , of integrated control are being established, as in cassavas, roses and others. Diverse responses have also been obtained from v¢eties of a single host plant species, 1Supported by CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico), Brasil, and FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo), Brasil.

4

Progress in Acarology- Volume 2

whether annual or perennial. Quoting Gerson again: "Such variation, while cautioning us against all-sweeping statements, may also help to reconcile the quite different results sometimes obtained in studies of plant-mite interactions." Very little has been reported on plant disease/phytophagous mites interactions. Some observations have demonstrated that certain diseases tend to displace mites; would this be related to the effect of leaf microclimate? These considerations suggest that researchers on plant mites could benefit from closer · cooperation with plant physiologists and plant pathologists.

REFERENCE . Gerson, U. 1979. In: Piffi, E. (ed.) Proc. tlth Internat. Cong. Acarol. Akademiai Kiado, p. 235..

.

.