2010-tpff-07 Host of Bactrocera invadens in Africa: Determination of host records and the trade consequences of a newly introduced pest to Africa. Jh venter

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Host of Bactrocera invadens in Africa: Determination of host records and the trade consequences of a newly introduced pest to Africa.

JH Venter
1. Introduction.
A new undescribed fruit fly pest was detected in Africa in 2003 in Kenya. Almost at the same time it was also found in Tanzania and very soon thereafter it was detected in several African countries from East to West Africa. Several hosts were recorded from the very start and by 2005 this pest was described as Bactrocera invadens Drew Tsukura & White (Drew et al. 2005).

It was also described s a fruit fly species which is part of the Bactrocera dorsalis species complex (Dew et al. 2005). B. invadens probably originated from Sri Lanka, although it also occurs in India and Buthan.

2. Distribution records.
The detection of B. invadens in Africa set in motion new support for Africa for proper fruit fly surveillance. Several African countries were surveyed and the pest were detected all along the equator as far North as Sudan and Senegal and as far South as Angola and Tanzania by 2006 (De Meyer et al. 2010). By 2008 Zambia, Mozambique (Correia et al. 2008) and later on Namibia reported that the pest were detected in their countries. Mozambique and Namibia however reported that it only occurs in isolated areas in the northern parts of their territories.

Several southern African countries did not initiate surveillance for this pest and information regarding the spread lacking in countries like the Democratic Republic of the Congo, Malawi, Botswana and Zimbabwe.

South Africa started with pilot surveillance projects at port of entries to detect Methyl Eugenol and Cue lure respondent fruit flies already in 2000 and increased the activities after the detection of B. invadens in Kenya. By 2006 a national exotic fruit fly program was launched focussing on port of entries, urban areas in the major cities, production areas and road transects (Barnes & Venter, 2006).

After the detection of B. invadens in Mozambique, Swaziland also invested in surveillance program and Mozambique developed an intensified surveillance programme mostly to try and identify possible pest free areas.

3. Host Records.
With the identification of a new invader pest in Africa a new flurry of hosts were determined from mainly field records after fruit has been collected, partly because it was the only surveillance method in many of the remote areas in Africa (Ekesi et al. 2006; Ekesi & Billah, 2006). Host plant records are essential to develop proper control strategies. It also serves as a reference for importing partners to develop phytosanatary conditions and without it a pest risk analysis would not be possible.

Early indications is that B. invadens like the other species in the B. dorsalis complex has a preference for Mangoes. Other preferred fruit documented was mangoes , citrus , and bananas(Rwomushana et al. 2008). The pest also earned its name in that it was found in several indigenous fruit hosts very soon after the first time it was detected in fruit fly traps in 2003 (De Meyer et al. 2010). Many of the host records recorded initially was from fruit that has been collected in field conditions (Mwatawala et al. 2006) . Not much fruit collection took place in the southern African country detections which should be a priority as the plant growth patterns changes from equatorial Africa towards the drier African Savanna and the southern African lowland coastal regions. Most the host records published did not provide much details on the condition of the host fruit or the fruit varieties detected (Mwatawala et al. 2006; De Meyer et al. 2010).

Laboratory choice and non choice tests have been conducted which provided much more clarity on the preferred hosts of B. invadens (Rwomushana et al. 2008). It also created more questions, as several of the hosts in the study which was indicated may be conditional hosts and fruit varieties and cultivars was not always indicated. Bactrocera invadens can already be seen as a polyphagous pests (Rwomushana et al. 2008) and as part of the B. dorsalis species complex may then also oviposit as a result of egg pressure on several possible surface areas if put under stress situations in a laboratory or field cages (Anonymous, 2008). Several economically important hosts recorded are also hosts of several other species within the species complex. However some of those hosts like avocado pear, and bananas the susceptible cultivars and host condition most preferable for ovipositing has been recorded for some of the other B. dorsalis complex species but not yet for B. invadens, or has been recorded once or partly. A summery of some of the hosts recorded for B. invadens, B. dorsalis and other of the B. dorsalis species in the species complex is indicated in Table 1. Host records of several B. dorsalis complex species is difficult to determine, especially in areas where more than one species occurs as identification of the actual species is difficult to determine. Several hosts has been recorded under unidentified species of the complex. Those are often also very unusual hosts or the only recording of some of the hosts like Vitis sp. (White & Elson Harris, 1994). This can lead to assumptions by importing countries of the real host range of B. dorsalis and or other species in the complex when they conduct pest risk analysis or when they furnish detection records.
4. Phytosanitary consequences for several African countries after initial host records of Bactrocera invadens was published.
Although most of Africa is still producing fruit for the local market and for subsistence use, several export initiatives has been set in motion for some African countries and the prospects of several African countries to be able to produce export quality fruit in a sustainable manner increased before B. invadens established and invaded the African continent. South Africa has been a major fruit exporting country form many years to countries across the globe. However most of South Africa’s trading partners does not have B. invadens in their respective territories. As no post harvest treatments has been developed yet for this fruit fly the risk to the economy is enormous. South Africa is also a major importer of fruit from several African countries and host material produced in countries where B. invadens occurs is a major risk. Subsequently South Africa had to take strict phytosanitary control measures for fruit entering from infested countries. For most fruit hosts no alternative mitigation option like a pest free area, or post harvest treatment, could be determined and it was prevented from entering South Africa. This included hosts like Musa sp., Persea sp. and Citrullus sp. Fruit imports from Northern Namibia came to a stop to South Africa as their only exporting country. Several other African countries like Senegal suffered major losses on Mango exports to the EU as a result of import interceptions. The United States Department of Agriculture also issued a Federal Order to control imports of host material from infested African countries.

A further consequence for Southern African fruit producers are that several of the hosts recorded is not traditionally fruit fly hosts in the area. Hosts like Lycopersicon, Capsicum, Musa and Persea spp. does not normally suffer from fruit fly damage. Not even Ceratitis capitata creates problems on avocado in South Africa (De Graaf, 2009) and there is therefore no production control systems in place (cultural or chemical) for fruit flies, or any pesticide registered on these crops against these pests, like a pesticide and protein lure mixture for bait application control.

In an African situation where there is predominantly small holder farmers, chemical control in any form is expensive and difficult to maintain. Production areas are often scattered over the large areas and to do proper host determination provides challenges both in terms of financial backup as well as logistical support. Repetitions of specific trials are difficult to execute and collection of fruit and transport to laboratories can result in physiological changes in fruit which makes them more susceptible to ovipositing. Avocado’s for example which is harvested in a rock hard state is not a susceptible host to many fruit flies, but ripening starts after harvesting and conveying to a laboratory for host tests may take several days. Although Avocado has been used in host determination trails, the cultivar was not indicated and specific results were also not indicated. However in field collections avocado was indicated in a previous publication as a host. South Africa developed their import regulations therefore according to the available information, which lead to a point where there is still no proper mitigation agreement accepted between Kenya and South Africa.

Proper cultivar selection may be the only solution to manage B. invadens together with other cultural control methods. Several examples already exists for Bactrocera dorsalis for host selection for fresh fruit to be exported from Mexico and Hawaii to mainland USA (Aluja et al. 2004; Liquide et al. 1995).

Host determination is a scientific process that can alter the course of trade very dramatically, but if done correctly can assist NPPO’s or RPPO’s to conduct proper pest risk analysis if data is documented comprehensively and systematically in laboratory and field conditions as not host is at all time susceptible to fruit fly attack and it may differ between cultivars (Pena et al. 2006). Several systems as been developed and can be followed but may be difficult to implement while fruit is collected in general surveys, but it is important as it is in specific host studies to ensure that cultivar, status of fruit development is recorded (Anonymous, 2008). Repetitions of studies may also reveal a better indication of when and under which conditions fruit flies will oviposit on different fruit hosts (Follett & Hennessey, 2007). Polyphagous fruit flies like B. dorsalis may oviposit on fruit depending on the availability of fruit or any surface suitable for ovipositing in the absence of preferred fruit hosts. This can be an indication that these fruit flies may utilise any available hosts in an area when preferred hosts are not available, or it means that even in choice tests unusual hosts may be utilised for ovipositing (Anonymous, 2008). It is therefore important that NPPO’s collaborate with research organisations and other role players in a newly effected territory to ensure host determination is conducted as complete as possible, where variety, cultivar and state or condition of fruit is documented when collected or in case of laboratory tests, what the condition of fruit was at ovipositing in field cages.

A proper standard to determine host status is essential, especially for developing countries that must rely on their existing limited resources and to make the most out of that.

6. Selected references.
Aluja, M., F. Diaz-Fleischer, and J. Arredondo. 2004. Nonhost status of commercial Persea americana ‘Hass’ to Anastrepha ludensAnastrepha obliqua, Anastrepha serpentina, and Anastrepha striata (Diptera: Tephritidae) in Mexico. J. Econ. Entomol. 97:293–309.
Anonymous.2008. NAPPO regional standards for phytosanitary measures No. 30, 06/11/2008 draft: guidelines for the determination and designation of host status of a commodity for fruit flies (Diptera: Tephritidae). The Secretariat of the North American Plant Protection Organization, Ottawa, ON, Canada.

Barnes, B., Venter, J.H. 2006. The South African fruit fly action plan. Area wide suppression and exotic species surveillance.(In: Fruit Flies of Economic Importance: From Basic to Applied Knowledge Proceedings of the 7th International Symposium on Fruit Flies of Economic Importance 10-15 September 2006, Salvador, Brazil. p 271-283.

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