|Protein Bait Spraying|
|Thursday, 31 January 2013 14:19|
The use of bait sprays comprising an attractant and a toxicant dates back to 1889 in Australia. The bait or attractant then was usually a molasses or sugar solution and the toxicant was usually a stomach poison such as lead arsenate or Paris green. Subsequent developments tended to focus on the insecticide component of bait sprays and the bait component was nearly always sugar and molasses. This approach changed with Steiner's work on the use of protein hydrolysate as an attractant for bait sprays in Hawaii in the early 1950s. These bait sprays were based on acid hydrolysates of a plant protein (usually derived from maize). They were used in Australia in this basic form for about 15 years, until the mid-1980s, when the acid hydrolysate component of bait sprays was replaced with a yeast autolysate.
The protein bait acts as a food attractant and its effectiveness relies on the fact that immature females need a protein meal for developing mature eggs. The bait spray residue on the foliage is ingested by the flies and kills them. Because the bait spray relies on its attractant properties for its mode of action, overall coverage of the tree canopy is unnecessary and a 'spot spraying technique' is adequate. Experiments and experience indicate that bait spraying is most effective in 'area' treatment programs. It is ideal for medium to large orchards or where adjacent properties use the technique. The method has been used to control fruit fly in the major citrus growing areas in Queensland for over 25 years and has proven very successful. This technique is now being used as one component of quality assurance schemes for export produce. For example, it is being used as a field control method for mangoes grown in Fiji Islands for the Japanese market. Similarly, protein bait sprays have been included in quarantine protocols developed between Fiji Islands, Tonga and Cook Islands and New Zealand for the export of eggplant, some chillies, watermelons and breadfruit.
Most bait sprays used in other parts of the world still rely on acid hydrolysates for their protein source, but in Pacific Island Countries and Territories (PICTs), Australia and South-east Asia, a different protein formulation has been produced in recent years. The most commonly used protein now is a yeast autolysate produced by enzymatic autolysis. The protein hydrolysate used previously was manufactured by hydrolyzing a plant protein with hydrochloric acid. This resulted in a protein bait with a low pH. Excess acid was neutralised with sodium hydroxide leaving a salt residue in the bait. Application of this type of bait spray often caused burning of fruit and foliage. There is minimal salt in the yeast autolysate used now so problems of phytotoxicity do not normally arise.
The yeast autolysate produced in Queensland is a light brown liquid, containing 420 g per litre of protein. It is marketed under the name Mauri's Pinnacle Protein Insect Lure (MPPIL), and can be stored at ambient temperature provided it is kept in a cool dark place. Refrigeration or air-conditioning will extend storage life and is recommended if possible. In Malaysia, the protein source used in bait sprays is a yeast autolysate produced as a by-product of the brewing process in the production of stout. It is marketed under the name of 'Promar'. It has proven to be an excellent attractant for local species of fruit flies. The implementation of a bait spraying program for fruit fly control with carambola using the new protein formulation has been very successful, resulting in a doubling of carambola production in Malaysia.
A plant to convert waste yeast from the Royal Brewery in Tonga into yeast autolysate was established. This plant converts waste yeast into protein autolysate through a process of heating and the addition of the enzyme papain and the food preservative potassium sorbate. The product, known as ‘Royal Tongalure’, was officially launched in early 1998 and is available to Tongan farmers at a much lower price than imported MPPIL. A similar plant was established in early 2001 in Vanuatu, run by Vanuatu Tusker Brewery.
Mauri's Pinnacle Protein Insect Lure (Australia) Promar (Malaysia) Royal Tongalure (Tonga)
Available sources of protein for bait spraying
The major disadvantage of protein bait sprays is that control may not be totally adequate at times of extreme pest pressure, especially if re-invasion of the treated area is continuous, and where the treated area is small in relation to untreated, surrounding areas. Control may also be less effective as the season progresses and populations with females at all stages of sexual maturity develop. Studies have shown that gravid female Queensland fruit flies are less interested in food than in finding suitable egg-laying sites. Additionally, in areas or during periods of high rainfall, significant amounts of bait solution may be washed off tree leaves.
On the other hand, the advantages of protein bait sprays far outweigh the disadvantages. Protein bait sprays are less harmful to beneficial insects, making them suitable for use in IPM programs. Because of the spot spraying technique, there is less insecticide applied to the crop or tree and non-target species have more refuges. Costs are considerably lower as less material is used per tree or per hectare. In addition, spot spraying is less time consuming than for cover spraying and therefore less demanding of labour. Farmers may also be able to use simple, inexpensive spraying equipment. Bait sprays are more environmentally sound because of reduced pesticide usage and less risk of spray drift. Spray applications can be directed on to foliage and away from fruit to minimise fruit residue problems. Reduced pesticide usage and use of coarse sprays at low pressure result in fewer hazards to the spray operator.
If Royal Tongalure is used, 100 ml of Royal Tongalure per litre is recommended, because protein is less concentrated than MPPIL. About 50 ml of bait solution is sprayed on the undersurface of 1m² of leaves on each tree. Every tree in and surrounding the orchard or village is sprayed. In vegetable gardens, such as capsicum and chillies, or cucurbit crops, 20-25 litres per hectare are sprayed as a band of coarse spray on the foliage of every third row. Sprays are repeated every seven days, starting one month before fruits mature. In some situations, protein bait spraying should be commenced soon after fruit set (e.g. capsicums and chillies in Tonga) or as soon as fruits become susceptible (e.g. carambola in Papua New Guinea or Palau). In very rainy areas, the spray interval should be decreased to every five days.
To overcome the problem of bait being washed off leaves and to improve the effectiveness of bait sprays, Aventis CropScience (Australia) developed a new formulation, with fipronil instead of malathion and an additive that forms a gel that sticks to tree leaves and resists rain. The new product, known as BactrogelTM has been used since late 1998 in the fruit fly eradication programme in Nauru and is available to countries that have registered fipronil insecticide.