PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL APPENDIX 10
Bionomics and
management of major
thrips species on
agricultural crops in Africa
R.T. Gahukar
Abstract: Several thrips species are known to cause serious damage to
agricultural crops in Africa. However, only five species of the family Thripidae are
considered as economic pests, namely, Frankliniella schultzei (Trybom),
Megalurothrips sjostedti (Trybom), Scirtothrips aurantii Faure, Sericothrips
adolfifriderici Karny and Thrips tabaci (Lindeman). Nymphs and adult thrips suck
the sap from leaf buds, leaves, flower buds, flowers and fruits, which become
deformed or remain underdeveloped, often showing scars. Sonic species act as major
vectors of viral plant diseases. Current pest-control practices include using
resistant plant varieties, biological agents, cultural operations and chemical
pesticides. However, more information is needed to formulate an effective, low-cost
and eco-friendly pest-management strategy that can be adopted sustainably in the
existing agricultural framework.
Keywords: thrips species; pest status and bionomics; control measures; IPM
The author is with Arag Biotech Pvt Ltd, Plot 220, Reshimbag Road, Nagpur 440009, India.
Tel: +91 0712 2747408. E-mail: gahukar_ngp@sancharnet.in.
Thrips form a small group comprising about 140 species of
over 70 genera among the insects attacking agricultural crops
in Africa (Faure, 1968; Bournier, 1971; Palmer, 1990). Most of
the crop pests belong to the family Thripidae within the suborder
Tenebrantia. Taxonomic reviews are available on
species found in central Africa (Priesner, 1952), west Africa
(Bournier, 1971; Okwakpam and Youdeowei, 1980; Pitkin and
Mound, 1973) and southern Africa (Faure, 1968) The familygroup
classification has been discussed by Mound, Fleming
and Palmer (1980); and genera, species and subspecies
relationships have been revised by Bournier (1971), Mound
and Palmer (1981) and Palmer (1990).
The economic importance of each species has not been
studied in different ecosystems where agricultural crops are
cultivated, either under sustainable or commercial
management, probably because thrips, being small in size, are
difficult to see with the naked eye. Pest damage is often
overlooked, as early symptoms of plant damage are not
clearly visible and late symptoms can be confused with those
of other sap-sucking insects such as aphids, jassids and
Outlook on AGRICULTURE Vol 33, No 3, 2004, pp 191-199
whiteflies, which occupy the same niche. In such cases, thrips
can be distinguished from other insects by the presence of
short, segmented antennae and narrow wings with greatly
reduced venation and marginal setae.
Thrips species are mainly plant feeders, although some of
them are casual visitors, gall makers or predators. Plant
injury during early pest attack is not easily detected, but late
attacks become progressively obvious and in severe cases,
plants wilt and die. For identification and overall estimation
of population density, thrips from shoots, flowers or leaves
are picked up with a fine brush, or plant parts are shaken or
beaten over a small plastic tray or a sheet of white cloth. The
collection can be safely preserved in a fresh mixture of 60%
ethyl alcohol (10 parts) + glycerin (1 part) + acetic acid (1
part). This mixture keeps the specimens soft and distended,
and facilitates slide preparation.
Limited studies of life history, damage potential, pest
ecology and control measures have been undertaken, mainly
in Nigeria, Senegal, South Africa and Kenya. This paper
reviews these works and identifies the lacunae in research
and development of the bionomics and
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