“Key Informant Survey” of Production, Value, Losses and ... - DfID

Appendix IV.C. Farm Field Assessments of Fruit Flies (Diptera: Tephritidae) in Pakistan:
Distribution, Damage and Control
John Stonehouse a *, Riaz Mahmood b , Ashraf Poswal b , John Mumford c , Karim Nawaz Baloch d , Zafar Mahmood
Chaudhary e , Arif Hamid Makhdum f , Ghulam Mustafa g and David Huggett c
a Department of Environmental Science and Technology, Imperial College of Science, Technology and
Medicine, University of London, Royal School of Mines, London SW7 2BP
b CABI Regional Bioscience Centre, PO Box 8, Rawalpindi, Punjab, Pakistan
c Imperial College of Science, Technology and Medicine, Silwood Park, Ascot SL5 7PY
d Agricultural Extension Service, Dera Ismail Khan, NWFP, Pakistan
e Agriculture Extension Department, Rahim Yar Khan, Punjab, Pakistan
f CABI Bioscience, Mardan, NWFP, Pakistan
g Ayub Agricultural Research Institute, Faisalabad, Punjab, Pakistan
*Corresponding author. Tel 020 7594 9311 fax 020 7589 5319 E-mail j.stonehouse@ic.ac.uk
Crop Protection – 21 (2002): 661-9
Abstract
The abundance and distribution of fruit fly infestation in melon, guava, jujube and mango were assessed in
farmers’ fields, under different control regimes, in four areas of Pakistan. Larval distribution was not clustered
among trees but was highly clustered among fruit. The mean number of larvae per infested fruit was not constant,
and was not significantly less variable than the infestation rate. In comparisons of Bait Application Technique
(BAT) with farmer controls, in melon, average season-end fruit infestation was 29% in unprotected fields and 5%
in those protected by BAT; in guava infestation was 44% in unprotected orchards and 12% in orchards
protected by BAT; in jujube, infestation was 16% in unprotected orchards and 4% in those protected by BAT.
Fifteen farmer-managed trials found BAT-treated melon fields yielded 37% more than unprotected and farmers
reported considerable satisfaction. Soaked-block Male Annihilation Technique (MAT) was compared with farmer
practices of no control: average infestation before harvest was 9% in unprotected plots and 0 in those protected.
Additional to differences in infestation rate, protected melon fields produced 17% higher yields of all fruit, and
protected guava orchards had 20% more fruit on trees, relative to those fallen, suggesting that fly attack
stimulated fruit drop, and loss estimates based on percentage infestation of sampled fruit may be underestimates.
If these reductions in infestation are extrapolated to loss estimates for Pakistan as a whole, the gross annual
saving inferred is 4915 million Pakistan Rupees or US$144.6 million.
Key words: Pakistan, fruit fly, on-farm controls, BAT, MAT, distribution
Introduction
Fruit flies are estimated to cause annual losses to fruit and vegetable farmers in Pakistan of over US$200
million (Stonehouse et al., 1998). This study aimed to evaluate aspects of their distribution, damage and control,
using realistic applications in farmers’ fields, and to develop for this a suite of assessment techniques sufficiently
accurate to quantify fly populations, and sufficiently robust to allow data to be gathered under difficult field
conditions.
The study looked at the presence and infestation levels of different species in different crops, and when
and how quickly infestation built up. The spatial distribution of infestation among trees and fruit was also
studied. If attack is clustered among trees in “hot spots” in the field, as opposed to randomly or evenly
distributed, more effort is required to assess infestation, and control efforts may need to be localised. The
distribution of larvae among fruits affects the relationship between the infestation rate, which is the frequency of
fruits containing one or more larvae (directly affecting economic because any infested fruit is largely
unmarketable), and the size of the larval population present, which is the product of the infestation rate and the
mean number of larvae per infested fruit. Changes in larval population size may result in changes in either or both
of these component quantities.
If the distribution of larvae among fruits is random, a change in the size of the total larval population
would involve changes in both the infestation rate and the number of larvae per infested fruit. If, however, the
number of larvae per infested fruit is relatively constant (that is, if infestation is clumped), then changes in the
total larval population would be a direct function of the infestation rate. The relationship between population size
and economic loss depends on which of these two patterns (or intermediates) occurs. If the mean number of
larvae per infested fruit remains constant, population control will be directly related to loss reduction. However, if
it does not remain constant, and the number of larvae per infested fruit is the major determinant of population size
(and infestation rate relatively constant), then changes in density of larvae overall will not correlate well with
changes in infestation rate (and therefore economic loss), especially when the mean larval population is above
one per fruit. In this case control efforts at high infestation levels will produce relatively poor returns, and the
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