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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: avergis@iihr.kar.nic.in (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

ARTICLE IN PRESS

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.

References

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