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

Appendix II. Scientific Research on Fruit Flies in India
Summary
Much is known about the taxonomy, biology, damage and management of Tephritids in India,
and over 100 papers have been published in the last decade. Three areas can be identified where there
remains a requirement for further studies:-
1 - A synthetic study to bring together in a standardised and comparative assessment the effectiveness
of food baits and parapheromone lures, alone and in different combinations, for optimum cost-effective
on-farm control, and whether and how the optimum may differ between fly species, areas and crops.
2 - Social and economic studies of the real and actual usefulness of control recommendations to
farmers.
3 - Evaluation of the advantages accrued by wide-area controls, in terms of cost-effective benefits
from farm cooperation to gain scale-economies of control.
Incidence and Infestation
Fruit flies have been recorded as pests in India since the nineteenth century (Maxwell-Lefroy,
1905) and much is known about their incidence and distribution throughout South Asia (Kapoor, 1989,
1993; Kapoor et al., 1976, 1977; Agarwal, 1984, 1985, 1987; Agarwal and Kapoor, 1985, 1986, 1988).
Trap catches have been particularly widely studied and documented, and vary between zones,
predominant hosts and fly species (Gupta et al., 1992; Murthy and Regupathy, 1992; Mann, 1996; Patil
et al., 1996; Kumar et al., 1997; Verghese, 1998; Agarwal and Kumar, 1999). However, while trap
catches well indicate fluctuations of a single species in time such as seasonally or annually, they poorly
represent actual infestation losses, due to the extreme differential susceptibility of different species to
different lures, with some being attracted to none. Also, trap catches often correlate poorly with
infestation level at field level (Nasir Uddin et al., 2000b, Stonehouse et al., in prep.), perhaps because
lure traps attract males from great distances, as can be shown by trap catches in fields empty of hosts,
implying attraction from outside the farm (Nasir Uddin et al., 2000d). As a result, the relative role of
various species in economic damage is less well understood than their geographical distribution.
Biology and Pest Status
The main pests such as Bactrocera dorsalis, zonata and cucurbitae are well-studied.
Shukla and Prasad (1985) found that the key determinants of fly abundance were (1) host availability
(2) median temperature and (3) relative humidity. Similar studies have allowed the development of
ecological models, allowing accuracy in prediction of up to 74% for the judicious deployment of
controls (Verghese, 1998).
The study of the developmental biology, ecology and host preferences of fly species have shed
light on their propensity to cause damage to different crops. Infestation rates, and therefore crop
losses, as introduction risks as well as field estimates, may be illuminated by comparative assays of the
success of species in hosts, such as in speed of development or percentage survival, when reared in
the laboratory. For example, Dacus ciliatus in Gujarat is most severe in little gourd (GAU,
pers.comm.) and in laboratory choice experiments it also preferred little gourd to, in order, cucumber
and bitter, bottle, smooth and ridge gourds (Patel and Patel, 1998c); it also developed in little gourd
faster than five other cucurbits (Patel 1994). Similarly, Gupta and Verma (1995) found that melon fly
both had lower survival and slower development on sponge gourd than on bitter gourd and cucumber.
Table II.1 shows some “growth indices” for laboratory cultures in India.
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