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Crop Protection 23 (2004) 6163
Short communication
Economic evaluation of the integrated management of the oriental
fruit fly Bactrocera dorsalis (Diptera: Tephritidae) in mango in India
Abraham Verghesea,*, P.L. Tandona, John M. Stonehouseb
a Division of Entomology and Nematology, Indian Institute of Horticultural Research, Hesseraghatta Lake P.O., Bangalore 560 089, Indiab Imperial College London, Royal School of Mines, London SW7 2BP, UK
Received 2 January 2002; received in revised form 27 February 2003; accepted 4 April 2003
Abstract
Bactrocera dorsalis is a serious pest of mangoes in India. Between 1985 and 1996 assessments of the effectiveness of a locally
recommended IPM package, in comparison with no control, on a susceptible variety were carried out near Bangalore. The IPM
package was applied over the 45 days before harvest and comprised (1) weekly removals of fallen fruit, (2) 3-weekly inter-tree
ploughing and raking and (3) three fortnightly cover sprays of insecticide. Infestation reductions attributable to the package were
between 77% and 100% in different years. Cost-benefit returns were dependent on the level of pest pressure, and in years of low
pressure the package may not recover its costs, necessitating a threshold approach.
r 2003 Elsevier Ltd. All rights reserved.
Keywords: Bactrocera dorsalis; Fruit fly; IPM; Mango; India; Cost-benefit analysis
1. Introduction
The Oriental Fruit Fly, Bactrocera dorsalis (Hendel)(Diptera: Tephritidae), is a major pest of mangoes in
India, particularly the more commercially valuable
varieties (Verghese et al., 2003). The insect is distributed
throughout India; in the North it overwinters in pupal
dormancy but in the South it is active throughout the
year (Butani, 1979) and as a consequence damage in the
South is particularly severe.
Attack can be reduced by the collection and destruc-
tion of infested fruits, by sprays of contact insecticides
(Narayanan and Batra, 1960) and by the destruction
of pupae in the soil by inter-tree ploughing and
raking, by physical destruction or enhanced vulnerabil-ity to ant, staphylinid and carabid predators (Sivinski,
1996). In India the collection of fallen fruits for pickl-
ing is a common practice, though infrequently suffi-
ciently thorough to affect fly populations, and there are
hopes for the extension of the practice for orchard
sanitation. As adult fruit flies can reinvade an orchard
practising sanitation from unclean areas outside,
attempts to quantify the benefit of sanitation have been
unsuccessful.
The Fruit Entomology Laboratory of IIHR has
developed an Integrated Pest Management (IPM)
package for the management of B. dorsalis on mangoin South India. It comprises (1) orchard sanitation by
weekly removal of fallen fruit, (2) 3-weekly inter-tree
ploughing and raking and (3) fortnightly cover sprays of
insecticide (Verghese et al., 2003). This study aimed to
assess the economic performance of this package.
Like many crop pests, fruit flies vary between years in
the severity of their attacks. In such cases, control by the
application of a threshold rule may be the economic
optimum (Mumford and Norton, 1984). Threshold
controls are uneconomic, if the returns to controls are
less than their costs, when pest attack is light. Thus, an
important question is whether these returns are positivein years of light attackif so, controls may be applied
routinely and prophylactically; if not, then a programme
of supervised control to thresholds may be the better
course.
2. Materials and methods
The study was carried out in the research orchards of
IIHR outside Bangalore (12580N; 77350E). An initial
study of 11 unprotected mango varieties, carried out in
ARTICLE IN PRESS
*Corresponding author.
E-mail address: [email protected] (A. Verghese).
0261-2194/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0261-2194(03)00087-5
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1985 and 1986, found that the two most attacked
varieties were Banganpalliand Totapuri, with respective
mean infestations of 46% and 59%, and the two least
attacked were Dushehari and Langra, with respective
mean infestations of 2.5% and 4% (Verghese et al.,
2003). Subsequently, the IPM package was assessed in a
15-year old orchard ofBanganpalli. Ten trees at one endof the orchard were untreated, and 10 at the opposite
end treated with the IPM package; these areas were
separated by three rows of untreated buffer trees. The
comparison was repeated nine times between 1987 and
1996. Fly pressure was generally strong, as the protected
trees were surrounded by unprotected onesa realistic
situation in India where mango trees in backyards and
kitchen gardens are never sprayed.
All control practices were begun 45 days prior to
harvest. Orchard sanitation comprised the removal and
destruction of fallen fruits at 7-day intervals (six times).
Ploughing between trees, with raking in the basin below
each tree, was at 21-day intervals (twice). Insecticide
sprays were with a foot-operated high volume sprayer,
mixed with a neutral soap (Sandovit) at 0.5 ml/l at 15-
day intervals (three times). Sprays were directed onto
fruits and not the whole canopy, which reduced the
spray volume to 56 L from about 20 L for a whole-
canopy spray of a 15-year old tree. As the experimental
programme progressed, the principle was established of
using three different insecticides for each spray to
minimise the risk of the development of resistance. In
1987, all sprays were of fenthion 0.05% (subsequently
declared an insecticide for restricted use); from 1988
until 1991 all sprays were of deltamethrin 0.0028%;from 1992 until 1996 sprays were of carbaryl 0.2%,
followed by deltamethrin 0.0028% and dimethoate
0.06% based on an earlier IIHR recommendation
(Tandon et al., 1974), in accordance with persistence
of, respectively, 7, 13 and 3 days (Awasthi, 2001).
At maturity, 50 fruits were selected at random from
each of the 20 trees500 treated and 500 untreated
fruitand dissected in the laboratory for the counting
of fly larvae.
3. Results
Table 1 shows the infestation level and the number
of larvae per infested fruit in each plot and each
year. Infestation levels (assessed by two-way analysis
of variance after arcsine transformation to normalise
percentages) varied significantly between treatments
(F 62:01701; 8 ) though not among years
(F 1:16528; 8 ns). The mean number of larvae per
infested fruit varied significantly among years
(F 6:59717; 7) though not between treatments
(F 3:03391; 8 ns). The number of larvae per infested
fruit was not significantly associated with the fly attack
pressure, as given by the percentage infestation in the
untreated plot (for treated fruit Spearman rs 0:0174ns,
for untreated fruit rs 0:0952 ns). The protection
inferred to be provided by the IPM package was as a
reduction of between 76.7% and 100% of fruit infested.
Fly attack pressure was not significantly associated with
the inferred level of protection (rs 0:3 ns) but was with
net benefits (rs 0:96667 ). This relationship was
quantified by least-squares regression and fitted a straight
line better than with either or both values converted to
natural logarithms; the relationship was used to estimate
the minimum level of fly attack pressure at which the
IPM package repaid its costs, calculated using a range ofhypothetical prices.
Profitability depended on the ratio of the value of the
mango harvest to the cost of the control package, both
expressed in abstract monetary units per abstract field
area. When this ratio was 15 to one net returns to
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Table 1
Outcomes of the implementation of the IPM package for protection of mango against fruit flies, Bangalore
Year Per cent infestation Larvae/infested fruit % Inferred reduction Economic return
IPM Untreated IPM Untreated
1987 6.0 42.9 19.7 21.9 86.0 2685
1988 5.6 31.3 42.5 43.4 82.1 15731989 1.2 11.1 33.3 34.0 89.2 10
1990 0.4 31.6 9.1 16.7 98.6 2111
1991 6.0 26.0 11.7 20.9 76.9 1000
1992 2.0 22.0 2.0 20.0 90.9 1000
1993 0.0 38.0 23.4 100.0 2800
1994 7.0 30.0 18.4 33.0 76.7 1300
1996 3.0 16.0 18.3 8.6 81.3 300
Mean 3.5 27.6 17.2 24.7 86.9 14178
Variance 7.3 102.1 191.6 109.5 73.7 958996
Note: Given for each year are the percentage infestation and the mean number of larvae per infested fruit, for both unprotected and IPM treated
plots, the inferred percentage reduction in fly attack attributed to the IPM package, and the net economic returns to controls, assuming control costs
of 1000 and a value of an entire unattacked mango crop of 10,000.
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control averaged 8.8, and in none of the years did the
package show a negative return. When the ratio was 10,
the average control return was 7.1 and the package
showed a loss in 1 year (1989); however, when the ratio
was five the average return was 2.1 and the package
showed a loss in 2 years (1989, 1996). Net returns over
years did not significantly depart from a normaldistribution (KolmogorovSmirnov g 0:068 ns).
4. Discussion
The IPM package obtained good fly control at many
levels of fly attack pressure. Below a certain level,
however, control may not show a net return, so there is
scope for the application of controls according to a
threshold rule. In future the IPM package may be
further developed by the incorporation of male annihi-
lation through methyl eugenol trapping, food baits and/
or the replacement of synthetic pesticides with neem and
other botanical ingredients with economic and environ-
mental advantages (Verghese, 1998).
Acknowledgements
Thanks are due to the Director of IIHR for the
provision of facilities, Mr. B.B. Bopaiah and Mr. S.
Hanumantharayappa for orchard maintenance and
experimentation assistance and two anonymous referees
at Crop Protection for advice.
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