Operations
Sanitation & host plants
Sanitation
SIT is an integrated strategy; sterile fruit flies cannot do the job alone. Success with an SIT programme is dependent on being able to maintain a high ratio of sterile males to wild males in the field, to minimise the chance of a wild male mating with a wild female.
Good orchard/vineyard hygiene is essential in any fruit fly programme. Fallen fruit often contains fruit fly eggs or larvae, which will help sustain infestation in orchards and vineyards. In vineyards, fruit fly larvae can complete their development in fruit that ripens after the harvest, commonly referred to as na-trossies, as they dry out and become raisins. Green fruit that is stripped from trees early in the season cannot later serve as fruit fly hosts. Good hygiene in home gardens is no less important, as home gardens serve as the main reservoir of the fruit fly breeding population throughout the year.
All fruit fly-infested and fallen fruit must be removed and destroyed, for instance by pulping, placing infested material in black plastic bags and left in the sun, or burying infested material at least one meter deep. In vineyards, na-trossies are a major source of re-infestation and should be removed. Particular attention should be paid to home gardens. Where fruit trees have fruit that will not or cannot be used, this fruit should be completely stripped from the trees before it ripens and becomes attractive to fruit flies.
Host plant management
The greatest source of fruit fly populations is from infestation of fruit in gardens, neglected orchards and vineyards, and in alternate hosts such as municipal areas and in the veld. Unless these host plants and their localities are known and properly managed, fruit fly populations will never be reduced adequately. Fruit flies can even breed in small berries – it is critical that all potential breeding hosts and sites be identified and eliminated as far as possible.
Remove, bait or strip fruit from all identified fruit fly host plants. Fruit on domestic fruit trees that is entirely unusable due to fruit fly infestation should ideally be cut down.
Fruit collected from any of these host plants should be treated as described above in sanitation.
Effective host plant management and sanitation must be continued after the releases of sterile fruit flies has started. Any fruit, wild, domestic, or commercial, in which fruit flies can breed will be a severe threat to the success of the SIT programme.
Host Plants
OF MEDITERRANEAN FRUIT FLY AND CAPE FRUIT FLY
Medfly fruit fly and Cape fruit fly will infest all deciduous fruits, table grapes, citrus fruits, and a great many other fruits of trees or shrubs, wild or domestic, but to differing degrees. At the one end of the scale, guava, loquat, peach, and wild plum (Harpephyllum caffrum) are examples of fruits that are very readily infested fruit fly, while at the other end of the scale, lemon, avocado and olive are examples of fruit with very low infestation potential.
The list below is not a complete list. There are many, many wild host plants not mentioned here.
| Host name | Species |
|---|---|
| Apricot | capitata, quilicii |
| Apple | capitata, quilicii |
| Peach | capitata, quilicii |
| Nectarine | capitata, quilicii |
| Pear | capitata, quilicii |
| Plum | capitata, quilicii |
| Prune | capitata |
| Table grape | capitata, quilicii |
| Wine grape | capitata, quilicii |
| Guava | capitata, quilicii |
| Loquat | capitata, quilicii |
| Quince | capitata, quilicii |
| Orange | capitata, quilicii |
| Lemon | capitata |
| Grapefruit | capitata, quilicii |
| Pompelmousse | capitata, quilicii |
| Naartjie | capitata, quilicii |
| Mandarin | capitata, quilicii |
| Tangerine | capitata, quilicii |
| Bitter orange | capitata, quilicii |
| Sweet orange | capitata, quilicii |
| Kumquat | capitata |
| Wild orange | capitata |
| Kiwi fruit | capitata |
| Olive | capitata |
| Fig | capitata, quilicii |
| Persimmon | capitata |
| Cherry | capitata |
| Mango | capitata, quilicii |
| Avocado | capitata, quilicii |
| Pomegranate | capitata |
| Mulberry | capitata |
| Passion fruit | capitata |
| Coffee | capitata |
| Granadilla | capitata |
| Banana | capitata |
| Host name | Species |
|---|---|
| Lychee | capitata, quilicii |
| Youngberry | capitata |
| Blackberry | quilicii |
| Bramble | quilicii |
| Bug-tree | quilicii |
| Cherry solanum | capitata |
| Wild plum(Harpephyllum) | capitata |
| Date palm | capitata |
| Bell pepper | capitata |
| Medlar | capitata |
| Wild medlar | capitata |
| Tropical almond | capitata |
| Cashew | capitata |
| Kei-apple | capitata, quilicii |
| Monkey apple | capitata |
| Breadfruit | capitata |
| Cape gooseberry | capitata |
| Cherry Guava | capitata, quilicii |
| Tree tomato | capitata |
| Black nightshade | capitata |
| Natal plum | capitata |
| Rose-apple | quilicii |
| Wild waterlemon | capitata |
| Tomato | capitata, quilicii |
| Cucumber | capitata |
| Cucurbitaceae | capitata |
| Eggplant | capitata |
| Sapodilla | quilicii |
| Custard apple | capitata, quilicii |
| Wild asparagus | capitata |
| Pawpaw | quilicii |
| Papaya | capitata, quilicii |
| Sapotaceae | capitata |
| Un-Tongaans | quilicii |
| Coffee berries | capitata |
It will serve little purpose to list here every single host species documented by these various authors, as many either do not occur in South Africa, are only occasional or rare hosts, and/or are species that the average person using this manual is unlikely to encounter. The selected list given in this Annexure is therefore intended mainly to illustrate the wide variety of fruits infested by Medfly and Cape fruit fly but including all the more common host fruits as well as some fewer common examples. Fruit flies have been recorded from many wild species of indigenous and exotic plants from a large number of families. For the purposes of an SIT program, it would probably be best to consider any unknown fruit or berry as a potential fruit fly host unless proven otherwise.
Fruit does not necessarily have to be large to serve as a fruit fly host fruit. For example, the author of this manual, Brian Barnes, has collected fruit flies from milkwood berries, which are only about 5 mm in diameter.
The host plants listed below have been taken from the above references and are divided into four categories – major commercial fruit hosts; other fruit trees, ornamentals, and domestic hosts; other trees; and wild hosts. No attempt is made to indicate the relative degrees of susceptibility to fruit flies of these hosts, as this differs according to species of fruit and fruit fly, the specific locality, and can be subjective. However, some of the most susceptible include stone fruit, guava, loquat, quince and wild plum, H. caffrum.
Selected list of fruit fly host plants
Major commercial fruit hosts
Apple, apricot, avocado, citrus, coffee, date palm, grape, kiwi fruit, litchi, mango, nectarine, papaya, peach, pear, persimmon, plum, prune,
Other fruit trees, ornamentals, and domestic hosts
African mangosteen, black nightshade, cherry solanum, crab apple, custard apple, fig, granadilla, guava, imbe, kei apple, loquat, medlar, mulberry, Natal plum (num-num), pomegranate, prickly pear, quince, rose-apple, rose hip, Rubus spp. (brambleberry, youngberry etc.), strawberry guava, strawberry tree, tree tomato, wild asparagus
Other trees
Box thorn, bugweed, Cape ash, forest peach, ironwood, milkwood, monkey apple, Natal orange, sandalwood, sapodilla, wild olive, wild orange, wild plum, yellowwood
Wild hosts
Either or both of the two fruit fly species have been recorded from wild hosts belonging to a large number of families, including: Anacardiaceae, Cecropiaceae, Chrysobalanaceae, Curcubitaceae, Ebenaceae, Euphorbiaceae, Flacourtiaceae, Longanaceae, Malpighiaceae, Meliaceae, Myrtaceae, Oleaceae, Podocarpaceae, Rosaceae, Rubiaceae, Sapotaceae, and Solanaceae.
While some of these families may be absent or not well represented in South Africa, they are included to illustrate the very wide host range of Medfly and Cape fruit fly. There are likely to be even more wild host plant families with species susceptible to fruit fly infestation.
References
Barnes, Brian. 2007. Sterile insect technique for management of Mediterranean fruit flies in fruit production. ARC Infruitec-Nietvoorbij Institute for Fruit, Vine & Wine. Stellenbosch, South Africa
Fruit flies of Economic Significance: Their Identification and Bionomics, by IM White and MM Elson-Harris, 1994
Bionomics and control of the fruit flies Ceratitis capitata (Wied.) and Pterandrus rosa (Ksh.) in the Western Cape Province. AC Myburgh, PhD Thesis, 1956