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Class |
Arachnida |
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Order |
Acarina |
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Family |
Tetranychidae |
Tetranychus marianae is a pest of several annual crops and perhaps
certain perennials. This mite could also become important in pasturelands and
rangeland.
Widespread in the Pacific islands, like the Marianas, from where it was first
discovered. It is also found in the West Indies, Bahamas, Southern Florida,
Nicaragua, Argentina, Brazil and Southeast Asia.
Adults and nymphs of spider mites suck the sap from the leaves, causing the
area around the feeding punctures to become chlorotic and appear as conspicuous
whitish to yellowish stippling on the upper surface of the leaf. Under heavy
infestation, photosynthesis is greatly reduced and the chlorotic areas may
coalesce forming mottled yellowish interveinal patches. The leaves eventually turn yellow and
may become brown and scorched
and drop prematurely.
Egg. The microscopic spherical egg is hyaline
turning translucent white when about to hatch.
Larva. The newly hatched larva is
small, round, pale yellow with three pairs of legs and distinct red eyes. Upon
feeding, its body turns yellowish green with black side to
side marks on its back.
Nymph. The protonymph
has four pairs of legs and a greenish oval body. The deutonymph
appears like the protonymph but is bigger.
Adult. The adult is similar in shape as
the deutonymph but bigger (about 0.5 mm) and has relatively longer legs. The
newly emerged adult is pale orange and becomes
carmine red with dark lateral markings as it grows older. Female adults
are ovoid while the male adults are tapered towards the abdominal tip and remain
yellowish green like the proto- and deutonymphs.
The eggs are deposited singly and scattered on the lower surface along or
near the midrib or veins. The incubation period lasts 3-5 days. Protonymphal and
deutonymphal periods range from 1-2 and 1-3 days, respectively. The total
developmental period takes about 7-10 days for both sexes. Females are capable
of parthenogenetic reproduction with unfertilised eggs developing into males
exclusively. Mated females lay more eggs than
the unmated ones. The former is capable of laying an average of 134 eggs and the
latter 61 eggs during their entire lifetime. The colony produces webbing
located on the undersurface of the leaf.
These mites may be found on the underside of leaves, with the help of a
magnifying glass. Close
inspection would also show tiny spider webs on stems and leaves. Applying mist on
the plants before inspection will make the webs more visible.
Sweetpotato spider mite is a polyphagous species (i.e. it feeds on a wide
range of plant species). Its common hosts are Maxima
cucurbita, Passiflora edulis, Centrosema pubescens, Ipomea triloba, Merremia
vitifolia, Acalyphaa wilkesiana, Ricinus communis, and many more.
Biological control
Several species of coccinellid beetles, and phytoseeid mites (Amblysieus
linearis Corpus and Amblysieus
longispinosus Evans) prey on all stages of development.
Chemical control
Several insecticides/acaricides available for mite
control.
Amalin, D.M. and Vasquez, E.A. 1993. A handbook on Philippine sweetpotato
pests and their natural enemies. International Potato Center (CIP), Los Baņos,
Philippines. 82 p.
Baker, E.W. 1975. Spider mites (Tetranychidae: Acarina) from Southeast Asia
and Japan. U.S. Dept. Agr. Coop. Econ. Inst. Rpt. 25(49-52): 911-921.
Mata, I.C. 1984. Biology of sweetpotato spider mite, Tetranychus mariannae
McGregor (Tetranychidae, Acarina). Unpublished BSA Thesis, Visayas State College
of Agriculture, Baybay, Leyte, Philippines.
Gapud, V.P. and Raros, L.C. 1986. Guide to Philippine Flora and Fauna -
Water Bugs and Mites. Vol. VII. Natural Resources Management Center , Ministry
of Natural Resources and University of the Philippines. 204 p.
Vasquez, E.A. and
Sajise, C.E. . 1990. Pests of sweetpotato: Insects, mites and diseases.
Philippine Root Crop Information Service, Philippine Root Crop Research &
Training Center. 65 p.
Contributed by: Erlinda
Vasquez and
Vilma Amante |
