Introduction to fruit flies
Importance of fruit fly Bactrocera dorsalis
Distribution
Host range
Control measures
Lacunae
Part A: Introduction__________________________________ Soumya, C.B., 2 0 1 4 |_______ 1_
Fruit flies (Diptera: Tephritidae) are one o f the most economically important groups o f
insect pests world wide. There are about 4,500 species o f fruit flies (Drew and Roming,
1997) among which 2,000 are considered economically important and are widely
distributed in the temperate, tropical and sub tropical regions o f the world (Christenson
and Foote, 1960). O f which 5% o f these occur in India (Ramani, 1998). The first detailed
report on fruit flies from the Indian sub-continent was made by Bezzi (1913) who enlisted
the species from India, Pakistan, Myanmar, Sri Lanka and Nepal. Superior mobility, great
dispersive powers, high reproductive rates, movement through market chain and extreme
polyphagy are among the common traits o f Bactrocera species. Several Bactrocera
species are well-documented invaders o f horticultural crops and also rank high on
quarantine lists worldwide (Clarke et a l, 2005). Since these are o f quarantine importance
they are o f great concern to fruit producing countries where these species occur, requiring
them to re-evaluate and revise their control strategies. In countries where these species
have not been recorded, quarantine measures have been considerably strengthened to
minimise the risk o f their entry, establishment
and spread.
Among Bactrocera species the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)
(Tephritidae: Diptera), is a serious pest on a wide range o f fruit crops. Bactrocera
dorsalis is a highly mobile insect, although many aspects remain unclear, migration is
known to be a common event (Steiner, 1957; Iwahashi, 1972; Fletcher, 1987). Immature
adults can disperse over 60 km to find fresh food resources and breeding substrates
(Fletcher, 1987; Liu, et al., 2007; Steiner, 1957). However, dispersal into the area alone is
sufficient to ensure that the population o f the species gets will established. Bactrocera
dorsalis is considered a major pest around the world (Vargas et a l, 2009). It was first
recorded in Taiwan in 1912 (Drew and Hancock 1994). Over the following years, it was
found in most countries o f the Asia-Pacific region, from China to Hawaii (Aketarawong
et al., 2007). Fruit flies are known to attack many fruit crops in Taiwan, southern Japan,
throughout Asia, including Bhutan, southern China, India and Thailand (Butani, 1979).
Clarke et al. (2005) reported it as a threat to agriculture across Asia-Pacific. Bactrocera
dorsalis is o f quarantine significance to EPPO (European Plant Protection Organization),
APPPC (Asia and Pacific Plant Protection Commission), COSAV (Comite de Sanidad
Ph.D. Thesis
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Plant-Insect Interaction in Selerted Hosts of Fruit Fly (Baarocers dorsilis) .... Reference to Selected Mango Varieties
Part A ; Introduction__________________________________ Soumya, C.B., 2 0 1 4 j_______^
Vegetal del Cone Sur), CPPC (Caribbean Plant Protection Commission), lAPSC (InterAfrican Phytosanitary Council) and OIRSA (Organismo Intemacional Regional de
Sanidad Agropecuaria) countries.
Bactrocera dorsalis is a highly polyphagous species (M etcalf and Metcalf, 1992) and can
disperse using mosaic o f host crops available and take advantage of human agricultural
trade. It infests plants o f 40 families including many commercial fruits (Smith, P. H.,
1989; Vargas et ah, 1984; Vargas and Carey, 1990). The attack o f B. dorsalis on 173
different varieties o f fruit and vegetables has been reported by M etcalf and Metcalf
(1992). It is a destructive pest on a wide range o f tropical and sub tropical fruits and
vegetables (Ye and Liu, 2005a). To name a few, mango {Mangifera indica L.), guava
(Psidium guajava L.), custard apple {Annona squamosa L.), apple (Malus pumila M.) star
fruit (Averrhoa carambola L.), banana {Musa paradisiacal L.), orange {Citrus sinensis
L.), pawpaw (Carica papaya L.), peach {Prunus persica L.), plum {Prunus domestica L.),
and tomatoes (Lycopersicum esculentum M.) (Clausen et a i, 1965, Koyama, 1989). In
India this species attacks mango and causes serious loss ranging from 5-80% (Kapoor,
1993, 2004; Verghese et a i, 2002, Verghese and Jayanthi, 2001) and damage caused on
guava is up to 44 percent (Stonehouse et a i, 1998, 2005).
Almost half o f the world's mangoes are cultivated in India alone, with the second-largest
source being China (Jedele et al., 2003). Mango is usually available in India from March
to mid-August. During off season B. dorsalis survives on its alternative host, guava
{Psidium guajava) thereby completing several generations within a year. Guava is an
important crop commonly called as the poor m an’s apple. In India, guava occupies 3.2%
o f the total area under fruits contributing about 3.3% o f the total fruit production in the
country (Indian Horticulture Database, 2011). India is the second largest producer of
banana after China. These three fruit crops are commercially important hosts which are
severely damaged by fruit flies. In India B. dorsalis attacks commercial varieties of
mango (Verghese et al., 2002). Fruit fly eggs are laid into unripe or ripening fruit where
the larvae develop and feed on the pulp o f the fruits. Infested fruits are spoiled quickly
and often fall to the ground before ripening. If that controlled, growers may lose the
entire crop. Generally, the Oriental fruit flies are able to reproduce in most envirormients
and climates. It has strong adaptability to various climates and hence has spread beyond
Ph.D. Thesis
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Plant-lnsect Interaction in Selerted Hosts of Fruit Fly (Bactrocera d o ra lis] .... Reference to Selected Mango Varieties
Part A; Introduction__________________________________ Soumya, C.B., 2 0 1 4 |_______^
tropical Asia where the fly likely originated (Clarke et al., 2005). The more the spread o f
the flies the more synthetic insecticides are used. The accumulation o f insecticides in
fruits crops and environment causes problem in agro-ecosystem which lead to health
hazards in living organisms.
In the past decade, extensive use o f synthetic insecticides has resulted in environmental
pollution and in the development o f physiological resistance. It is essential to search and
develop control measures which are o f low cost and safe to environment. The
environmental and socioeconomic impacts o f controlling pests are so wide and
potentially deleterious (Lewis et al., 1997) that solving the problem has become an issue
o f national interest in many countries. Pest related problems have not only increased but
also, due to globalization, now impinge on society in ways never envisioned previously.
Fruit flies are considered the major pests that crucially require effective management
tactics. In many countries, quarantine laws restrict or prevent spread o f the fly. However,
each preventive method affects quality, storage period and cost o f fruit production, as
well as farmer’s health and environment. Progress has been made in managing the pest
by integrating different methods (Verghese et al., 2004b) like MAT (Male armihilation
Technique), BAT (Bait Application Technique) and field sanitation (Verghese et al.,
2011a). Male Armihilation Technique uses methyl-eugenol traps (Ishtiaq et al., 1999)
which contains ply wood block which is impregnated with the parapheromone methyl
eugenol along with an insecticide and are tied to the trees in the orchard. As this
technique only reduces the number o f males within a population, female flies can still
cause damage by attacking fruit. Moreover, male annihilation is not effective in the
situation where there is even modest immigration from nearby populations. This control
option is best suited to isolated envirormients like islands. In Bait Application Technique
(BAT), proteinaceous food is mixed with an insecticide and sprayed along the trunk o f
trees (Cornelius et al., 2000b; Pinero et al., 2009), where in the effectiveness o f this
control method may be reduced by rain washing off bait spots and the effect o f pesticide
getting degraded over time. Field sanitation, which involves hand picking o f fallen fruits
and burying them deep into the soil, either prevents development o f fruit fly larvae or
Ph.D. Thesis
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Plant-lnsect Interaction in Selected Hosts of Fruit Fly (Bsctroceri dorsilis) .... Reference to Selected Mango Varieties
Part A: Introduction
Soumya, C.B., 2 0 1 4
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4
sequesters young emerging adult flies so that they cannot return to the crop to breed.
Again, this is more time consuming and labour intensive.
The classical biological control of fruit fly (Vargas et al., 2007), is unsuccessful, due to
the rapid breeding o f the insect pest in a highly perishable host. There is a risk with the
release o f each natural enemy species that some non-target species will also be attacked
(Hoddle, 2004). Classical releases o f parasitoids were shown to be cost-effective where
natural enemies were non-existent, but augmentative releases, although promising, are
not a proven technology and cannot be sustained without a rearing facility.
Sterile Insect Technique (SIT) is to release a large number o f sterilized males to mate
with wild females, resulting in the production o f infertile eggs (Knipling, 1959). Some
SIT programs in the past have failed due to continuous immigration o f fruit flies from
other areas into the areas being targeted (Meats et al., 2007) and are also not economical.
Apart from these there are many post harvest treatments to control fruit flies which are
non-chemical quarantine treatments. Hot water treatment involves immersion o f fruits in
hot water which is maintained at a particular temperature for a specific duration o f time.
This treatment has been widely adopted because o f its efficacy (Jacobi et a l, 1995) and
low cost. However, hot water immersion may damage the quality o f fmits (Yahia and
Campos, 2000). Small fruits are generally damaged more readily by heat compared to
large fruits, as they get heated more quickly.
Vapour, the oldest method o f quarantine heat treatment, involves heating the host fixiit by
moving hot air saturated with water vapor over the fruit surface. Vapor heat treatment
(VHT) is a high humidity air treatment. Forced hot-air, also known as high-temperature
forced air, is a modification o f the vapor heat treatment developed by Armstrong et al.
(1989) to kill Mediterranean fruit fly, Melon fly and Oriental fruit fly eggs and larvae in
papaya. Hot water immersion quarantine treatment is relatively easy to engineer whereas
forced hot-air and vapour heat treatment equipment requires more engineering and
require complex computer programs to operate and monitor the treatment parameters and
equipment. Apart from the techniques discussed so far there are still more treatments, but
Ph.D. Thesis
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Plant-lnsect Interaction in Selected Hosts of Fruit Fly lB3arocer3 dorafe).... Reference to Selected Mango Varieties
Part A: Introduction__________________________________ Soumya, C.B., 2 0 1 4
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are not o f commercial importance as each treatment has its own limitations or
disadvantages.
The post-harvest heat treatments can damage the fruits both externally and internally.
External damage includes peel brownin, pitting, tissue damage caused by heat will result
in increased decay development, the fruit can soften quickly or show abnormal softening
where some areas o f the flesh remain hard while others soften (Jacobi and Wong, 1992;
Lay and Rose, 1994, Jacobi and Gowanlock, 1995). Internal damage in fruits can lead to
poor colour development, abnormal softening, lack o f starch breakdown and development
o f internal cavities (Mitcham and McDonald, 1993).
Food irradiation is a process by which products are exposed to ionizing radiation to
sterilize or kill insects and microbial pests by damaging the DNA o f target species.
Different irradiation doses are applied for different fruit flies. The mangoes for export to,
the United States o f America are irradiated with a minimum absorbed dosage o f 400
Gray. This method is effective in extending shelf-life and reducing decay, by killing,
sterilizing or preventing ftarther development o f a wide variety o f insect pests o f
quarantine importance on perishable fruits and vegetables. But, the drawback is that
irradiation is more expensive, facilities are limited and consumer acceptance o f irradiated
produce is very less.
Control o f Oriental fruit flies through plant’s secondary metabolites has been an
important and growing area o f research in recent years. Especially, the interactions
among chemicals metabolized by plants, insect herbivores, parasitoids o f herbivores, and
plant pathogens. This area is attributed to the expanding awareness and need to prevail
upon environmentally safe control measures to keep plant pests in check. Phytochemicals
possess a wide spectrum o f biological properties. Among phytochemicals, secondary
metabolites act as insect antifeedants, repellents, growth inhibitors, attractants or
chemosterilants (Bennett and Wallsgrove, 1994; Mazid et al., 2011). In addition, they are
biodegradable. Therefore, phytochemicals are potentially safe and economic to replace
synthetic insecticides especially in case o f fruit flies. Primary metabolites are the
substances produced by plants that are directly involved in growth, development and
Ph.D. Thesis
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Plant-lnsect Interaction in Selected Hosts of Fruit Fly (Bsctrocers dorsilis) .... Reference to Selected Mango Varieties
Part A; Introduction__________________________________ Soumya, C.B., 2 0 1 4
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6
reproduction. Secondary metabolites are not directly involved in growth or production
but they are often involved with plant defense against pests (Benneett and Wallgrove,
1994).
These compounds usually belong to one o f three large chemical classes:
phenolics, terpenoids and alkaloids. Among these, phenolic compounds have been
repeatedly demonstrated to play a vital role in plant resistance and protect fruits and
vegetables against pests (Lattanzo et al., 2006).
Use o f resistant varieties is most economical, effective and ecologically safe method of
protecting crops against insect pests since there is no special technology to be adopted by
the farmer (Helbig, 1997). The expenses to the farmer are limited because he only has to
buy the seedlings and health hazards associated with insecticide application are also
avoided. The use o f resistant crop varieties for insect control is based on either antibiosis
or antixenosis (Helbig, 1997). It is well documented that the oviposition in fruit flies
depends upon their decision to select the proper host which must support the activities of
their off springs (Fontellas-Brandalha and Zucoloto, 2004; Joachim-Bravo et al., 2001).
Other factors that may affect the oviposition preference in fruit flies include odour,
colours and shape o f host fruits (Bell, 1990; Diaz-Fleischer et a l, 2000; Jolivet, 1992;
Panda and Khush, 1995). Not surprisingly, physiological changes during ripening also
influence fruit fly oviposition behaviour (Messina and Jones, 1990; Messina et al., 1991).
The perusal o f literature revealed that there are limited studies on the behavioral response
o f B. dorsalis to different hosts, and biochemical basis o f fruit fly infestation and a very
few prediction models are available for IPM (Integrated Pest Management) intervention
to save the crops. All these facts discussed above called for initiation o f present study and
the following objectives were framed taking into account the above lacunae.
1) To study the preference o f B. dorsalis to selected hosts.
2) To study the behavioural response o f B. dorsalis to major host.
3) To find the biochemical basis for variation in host susceptibility or resistance.
4) To find the relationship between fruit maturation and fi^lit fly infestation with
reference to size and biochemical changes.
5) To understand the impact o f biotic and abiotic factors on the population o f B. dorsalis
to develop suitable ecological population model.
Ph.D. Thesis
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Plant-lnsect Interaction in Selected Hosts of Fruit Fly (Bactrocera dorsafo).... Reference to Selected Mango Varieties