PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

APPENDIX 10
PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL
Bionomics and management of thrips in Africa
or when sowing was done after maize (El-Mahal and Nasr,
1966). Transplanted cotton suffered less infestation than
normally sown cotton in Egypt (Radwan, Abdel-Hamid, El-
Sadaany and Romeilah, 2000). Late-sown onions (Dawood
and Haydar, 1996) and highly fertilized tomato (Omar,
Haydar and Afifi, 1993) suffered higher pest infestation.
Intercropping of onion with cotton planted in ridges (Sharaf,
Ismail, Ali and Hashem, 1993), or onion and garlic with
tomato (Afifi and Haydar, 1990) has been recommended.
Local onion cvs. Giza-6 and Behiri, currently cultivated by
farmers in Egypt, were found to be tolerant to thrips attack
(El-Gendi, 1998). However, further breeding to develop
resistant cultivars was not carried out.
Predaceous insects such as staphilinid, Paederus alfierii,
Chrysopid, Chrysoperla carnea Stephens, Coccinellids,
Coccinella undecimpunctata L., Scymnus spp., anthocorid, Orius
albidipennis (El-Gendi, 1998) and phytoseiid mite, Amblyseius
spp. are known to occur in fields when the thrips population
is high. Chyzik, Klein and Ben (1995) studied the biology of
O. albidipennis in the laboratory and found that thrips were
better prey than Ephestia cautella (Wlk.) eggs or Tetranychus
urticae Koch adults, on which up to 98% of the predators
survived.
Insecticides have been used extensively on agricultural
crops: eg carbofuran granules at 0.025 g a.i./onion plant or
0.24-0.53 kg a.i./ha, 1.08 kg a.i. malathion or phenthoate/ha
in Sudan (Kisha, 1979, 1983), and dieldrin at 70 g a.i./ha in
Kenya (Bullock, 1963). Other synthetic insecticides such as
quinalphos, dimethoate, fenvalerate, prothiophos, actellic
mixed with lannate, triazophos and cypermethrin gave >90%
kill a day after treatment on onion (Mourad, 1992; Dawood
and Haydar, 1996). Foliar sprays of phoxim, carbaryl,
pirimiphos-methyl, dicrotophos, chlorfenvinphos, methomyl,
mephosfolan, monocrotophos, dichlorvos and
methamidophos were also quite effective in reducing pest
numbers and plant-infestation levels (Halteren, 1970;
Swailem and Abul-Ela, 1975; Kisha, 1983). Two to five
applications at fortnightly intervals were necessary to control
the thrips populations in Ghana (Halteren, 1970), whereas
cypermethrin sprayed at 500 g a.i./ha on onion controlled the
pest in Ethiopia (Shimeles, 1998). Under South-African
conditions, Jacobs (1995) recommended the monitoring of
thrips with blue sticky traps at the ‘green tip’ stage of apple,
spraying of methamidophos between full bloom and 75%
petal fall, and again 1-2 weeks later.
In Egypt, when monocrotophos at 200 ml a.i./ha mixed
with a mineral oil (‘misrona’) or cotton-seed oil was sprayed
on cotton, there was an additive residual effect. On the other
hand, these mixtures proved to be toxic when monocrotophos
was sprayed at 400 ml a.i./ha. Popular insecticides (eg
acetamiprid, milbemictin or thiocyclam hydrogen oxalate)
proved to be inferior to monocrotophos in reducing pest
populations (Hamid and Korkor, 1999). In another trial,
monocrotophos gave a 70% kill 14 days after application,
although pirimiphos ethyl, furathiocarb, omethoate or
carbosulfan gave a better initial kill (Kandil, Barakat, Saleh
and Ibrahim, 1991). For increasing the bioactivity of a mixture
of dicofol + omethoate, an activator at 50% and an enhancer
or star oil at 25% was added (Moustafa, Abou-Seeda and El-
Attal, 1990). Among several insecticides tested for their
knock-down and residual effects, methamidophos, omethoate
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and monocrotophos were found to be promising, while
cyanophos and thiometon were the least effective (El-Dahan,
Kady, Khalil and Serig, 1990).
Pest management in cotton was studied in Egypt using
modern pesticides, where three sprays of methomyl at 3-
weekly intervals decreased the number of important
predators (Abou-El-Hagag, 1998a). Thus, safer pesticides
need to be identified and studied. For example, El-Hamady
and Sholoa (1999) recommended treatment of cotton seeds
with imidacloprid at 7 g/kg seeds. The residual effect of
imidacloprid lasted up to seven weeks after application and
later declined to 0.016 ppm. From this application, the activity
of catalase and invertase in the soil was significantly reduced
after 3-4 weeks, but the activity of dehydrogenase,
phosphatase and urease were least affected. As this technique
assures the safety of predators, a package comprising an early
sowing of imidacloprid-treated seeds, fertilizer management
and intercropping should be recommended to farmers.
Pulse thrips: Sericothrips adolfifriderici Karny
Synonyms of the species include S. occipitalis Hood and
Hydatothrips adolfifriderici Karny. This is a common thrips
species attacking pulses in Africa. It causes serious damage to
off-season (irrigated) cowpea (Taylor, 1974; Ezueh, 1981).
Thrips injury is initially responsible for scarring, yellowing
and silvering of leaves. Later, leaves become deformed and
brownish on the underside, and necrosis occurs. As the plant
grows, the pest attacks shoots and flowers, resulting in
stunted plant growth and flower drop. In Nigeria, plant
damage up to 42 days after planting did not affect cowpea
yield, but when 50% of the plants were damaged, a
significant loss in cowpea yield was observed (COPR, 1981).
An estimation of damage is done 25-30 days after planting on
a scale of 1-5, in which 1 = 0-1% of plants attacked, 2 = 2-5%, 3
= 6-25%, 4 = 26-50%, and 5 = 51-100% of plants attacked
(Taylor, 1964). Neither economic thresholds nor economicinjury
levels have been worked out in pulses.
Eggs are laid on aerial plant parts. After hatching, orange
or yellow nymphs gather on the underside of leaves.
Pupation occurs on the ground beneath the host plants.
Adults are 1 mm long with pale yellow antennae possessing
brown apical segments. The head is brown at the anterior
side up to the occipital ridge and pale yellow at the posterior
side. The wings are brown with a pale band on the base at the
rear; the legs are pale. Tergites IV and X of the abdomen are
pale yellow, whilst tergites VII-IX are dark brown. A
generation takes about two weeks, and several generations
may be completed depending upon the weather and the
availability of host plants. Dry weather is favourable for pest
development and heavy rains wash thrips off the plants
(Taylor, 1964; Ezueh, 1.981).
Insecticides have usually been used to control this pest in
cowpea. Four to five sprays at 7 to 10-day intervals of
deltamethrin at 25 g a.i./ha, monocrotophos at 200-400 g a.i.,
dicrotophos at 350-400 g a.i, dimethoate at 1.12 kg a.i.,
phosphamidon at 150-200 g a.i., or DDT at 1 kg a.i./ha
produced significant pest mortality (Nyiira, 1971; COPR,
1981). Similarly, granules of disulfoton, furadan and thimet at
1-1.5 kg a.i./ha, applied at planting or 20
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