Integrated control of citrus pests in China

• Guangdong Entomological Institute, China
• Queensland Department of Primary Industries, Australia

Citrus production is an important subsector of Chinese agriculture and has increased threefold (28% annually) since 1978. Commercial plantings are expected to reach 1 million hectares by the year 2000. Emphasis on the use of broad spectrum pesticides (e.g. carbamates, organophosphates) since the 1940s has led to almost complete dependence on their use. The current annual cost of applying pesticides in southern China is very high up to 20% of the gross value of production per hectare.

In contrast, the 32 000 hectare, $250 million, Australian industry has successfully used integrated pest management (IPM) programs, based on the use of introduced natural enemies and C21C23 petroleum spray oils. In the late 1980s IPM programs were estimated to be reducing spray costs by $4001000 per hectare annually, particularly for the control of citrus red scale and white wax scale.

The success of these IPM programs, however, and their wider adoption, are currently threatened by changes in the distribution and relative importance of the prevalent pests in Australia. Pink wax scale, Chinese wax scale, citrophilus mealybug, and citrus leaf miner are all becoming markedly more widespread inland. Other pests have also increased their distribution. Several strategies are currently being pursued to minimise the impact of these threats and improve IPM programs.

Citrus red scale research in NSW and in China in the 1970s and 1980s indicated that the introduction and establishment in Australian orchards of the thrips Aleurodothrips fasciapennis (Franklin) will significantly enhance citrus red scale IPM programs by increasing mortality of immature stages. Although this thrips occurs in Australia it has not been recorded on citrus since 1927 indicting the existence of different biotypes even though specimens collected from around the world are indistinguishable.

This project will build on the existing collaboration between the Biological and Chemical Research Institute (BCRI), New South Wales, Australia, and the Guangdong Entomological Institute (GEI), China. The main objectives of the research are to reduce the use of broad spectrum pesticides in China by implementing IPM programs and to improve Australian IPM programs through a greater understanding of the relative effectiveness of the natural enemies of citrus red scale and factors that influence their effectiveness, and through the introduction and release of a predatory thrips, Aleurodothrips fasciapennis (Franklin).

Scientists at BCRI and GEI will analyse existing citrus red scale data sets in Australia and China and construct life tables. At BCRI the scientists will use molecular biology techniques to determine the the levels of genetic variation in the different populations of A. fasciapennis using live organisms collected in Queensland and southern China. They will also use the polymerase chain reaction to selectively amplify DNA sequences and polyacrylamide gel electrophoresis (PAGE) to compare proteins.

Based on existing technology at GEI, researchers will rear A. fasciapennis in thawed rice moth eggs and on citrus red scale infested butternut squash or other cucurbits. They will use the cultures for laboratory studies on the biology of the thrips and on its response to prey; the effect of predation on the reproductive capacity of the hosts; and population growth statistics.

Field studies will be carried out in Guangzhou or Shaoguan in southern China to study the phenology of fruit trees in relation to pest populations and the role of nitrogen on the reproductive capacities of the scales. The scientists will construct life tables to determine the relative importance of natural enemies.

Current citrus research funded by the Horticultural Research and Development Corporation in collaboration with two petroleum companies will form the basis for tests in China on imported C23, C21, and C19 oils and comparison with locally produced oils and other commonly used pesticides for a variety of citrus pests. A novel citrus leaf miner spray oil (patented by NSW Agriculture in 1992) will also be tested .

A successful outcome to the project will benefit the Australian citrus industry with savings in spray costs estimated at $2 million per year as well as savings of up to $1 750 per hectare from reductions in downgraded fruit.

The Australian manufacturing industry also stands to benefit as the petroleum based oils are not produced in East Asia and Australian refineries are developing markets in the area. The project will also enable quarantine tests required for the release of A. fasciapennis in Australian orchards to be carried out in China at significantly lower costs than in Australia.

The benefits to China will include a reduction in the current unacceptably high pesticide spray costs, reduced pollution with pesticides and pesticide residues in fruit and reduction in health costs associated with the use of hazardous chemicals.