Protein is a very important component of the diet of tropical fruit flies.
After the young flies emerge from the soil, the females in particular seek out and feed on protein on leaf and fruit surfaces, especially in host fruit plants.
Protein promotes growth to sexual maturity and after the female flies develop eggs, they lose interest in this food source and begin to lay eggs.
Protein as an attractant has been researched for more than five decades. It has proven to be a poor attractant in traps, but highly effective when sprayed on to foliage, particularly for the immature females.
With the withdrawal of effective systemic cover sprays for fruit fly control in Australia, there is a genuine need to develop alternative technologies and revisit old ones.
One option is protein bait sprays. In this article I review the historical development of protein bait spray formulations, recent research, their applications and efficacy.
Historical development
The use of poison baits to control fruit flies has its origins in the 1880s.
At this time in Queensland, Henry Tyson was recommending mixtures including treacle or molasses with quassia for poison. The mix was to be smeared on plates and left in orchards near ripening fruit.
By the early 1900s the distribution of ‘poisoned sweets’ before egg laying was being recommended for the control Mediterranean fruit flies in South Africa. This mixture, consisting of sugar, arsenate of lead and water, was developed by entomologist C.W. Malley.
In following years, in Hawaii, South Africa and Queensland, various entomologists used slight variations of this formula with variable success, some replacing sugar with molasses and others including glycerine for more adhesion.
In 1916, Maxwell-Lefroy published the ‘ideal’ fruit fly bait in the Queensland Agricultural Journal. It was a mixture of casein, brown sugar and water in equal parts. This appears to be the first record of protein being included in fruit fly baits.
Greatest advance in bait spray technology
By far the greatest advance in bait spray technology for fruit fly control was the incorporation of protein hydrolysate by Loren Steiner in Hawaii in the 1950s.
His mixture of protein hydrolysate, malathion and water was used as an aerial spray to eradicate Medfly from Florida in 1956 and 1957.
This bait spray was considered more effective when applied regularly and over large areas of fruit trees.
At the same time as Steiner was developing his protein hydrolysate bait spray, another worker in Hawaii, Paul Gow, concluded that the attraction of protein-based baits was due to microbial action and that the addition of certain bacteria to the bait mixtures markedly increased their attractancy.
More recent research
We looked into this concept further in the 1980s using bacteria isolated from Queensland fruit fly.
While the addition of certain bacteria markedly increased the attractancy of protein baits, commercial formulations could not be successfully developed.
I began my research into fruit fly bait spray technologies in the early 1970s and have since conducted bait spray research in northern and eastern Australia, countries in South-East Asia and the South Pacific, covering a wide range of crops, fruit fly species and formulations.
The research has been aimed at developing the most attractive and effective formulations and improving the spray application technology.
Two basic strategies
The research has involved two basic strategies:
- Ground sheet trials in which 2m x 2m white sheets are placed beneath trees in orchards to collect fruit flies knocked down by bait sprays that include a rapid-kill toxicant. The sheets can be arranged throughout an orchard based on a sound experimental design to compare different formulations. The numbers of female and male flies collected provide data for analyses.
- Field control trials in orchards where an entire crop was treated with one formulation.
These have been conducted on a wide range of crops such as citrus in Bhutan, guava in Vietnam, mangoes in Fiji, and stone fruit in Queensland.
First available protein baits in Australia
The first available protein baits in Australia were acid hydrolysates. These were so salty and acidic that they were phototoxic to plants.
Autolysed yeast protein baits became available in the 1980s and are still around today. These yeast based proteins are highly attractive to fruit flies, particularly immature females that require protein for egg production.
Gelatinised protein bait formulations
In the mid-1980s, while researching certain bacteria associated with fruit flies and their host plants, I developed the concept of gelatinised protein bait formulations, with the aim of providing a longer lasting substrate on the plant surface for bacteria to survive and metabolise the protein bait more effectively.
After a series of ground sheet trials, we demonstrated that gelatinised yeast proteins, with or without bacteria inoculum, were more attractive than water-based formulations.
Recent research has confirmed that gel formulations attract and kill significantly more fruit flies over a longer time period than water based formulations.
The insecticide used in the bait formulation also can influence the fly feeding activity and resulting kill rate. However, only those registered for each jurisdiction must be used.
Advice for using bait sprays
I recommend these steps to obtain the highest level of efficacy from the protein bait technology:
- Use a gelatinised yeast based bait
- Spray host fruit trees when fruit is mature green before fruit flies begin to attack fruit
- Spray early in the morning
- Spray bait in the upper canopy, rather than in the lower foliage
- Apply at five to seven day intervals, as there is little attractive bait remaining on the plant surface after five days.
I do not recommend these practices as they are not effective and waste resources:
- Do not spray on posts, fences, tree trunks and branches
- Do not spray on host fruit trees that are not bearing fruit
- Similarly, bait spraying vegetation surrounding an orchard has little impact.
Remember that protein baits and protein-based systems primarily attract and kill immature flies.
Older females that have laid eggs and are seeking protein for another egg cycle can also be attracted. Mature egg-laying flies that fly in are not attracted and killed.
No situation is the same
I have worked in orchards with a number of different fruit fly susceptible crops, each maturing at a different time, and in contrast monocultures.
In the former, long-term applications of protein bait and farm hygiene are important strategies.
Protein baits are most effective on fruit fly populations that are attracted to fruiting host plants. In these habitats, the fly populations often build up to a large level, and then become easy targets.
For more information contact AgNova phone 03 9899 8100
email
web www.agnova.com.au
See this article in Tree Fruit July 2016
