To achieve more environmentally friendly and sustainable agriculture, the use of synthetic pesticides needs to be reduced, and one of the strategies used is biological control. Biological control, based on the prey-predator concept, aims to reduce or control pest populations in farms without or with minimal reliance on chemical insecticides, thus preventing detrimental effects on humans, flora, fauna and plants.
Various types of biological control agents exist, including microbes, natural substances, insects, mites, nematodes, semiochemicals, parasitoids, predators, bacteria, fungi, viruses and pathogens. Biological control employs three techniques: the classical method, which involves introducing natural enemies to combat pests; the inductive (enhancement) method, which introduces large populations of natural enemies; and the inoculative (preservation) method, which is used, especially for predators that have been established in a habitat for an extended period.
One promising biological control agent is ladybird beetles or coccinellids. These beetles are a subfamily of the family Coccinellidae and can be found on every continent in the world, except Antarctica. This family comprises 6,000 species worldwide, of which 90% are considered beneficial predators. In Malaysia, approximately 2,000 species of this family have been recorded. Coccinellids are found inhabiting various environments, whether on land or in trees. Some species can even thrive in extreme conditions, including mountainous regions, arid deserts and cold climates.
Their life cycle, like that of other insects, comprises four stages: egg, larva, pupa, and finally the adult. The duration of the life cycle varies depending on factors such as temperature, relative humidity, rainfall and food sources. Adult female beetles can lay 200 to 1,000 eggs, typically near their primary food source, often in colonies of aphids and other plant pests. Newly hatched eggs are grey or black with yellow, orange and red stripes on their dorsal sides. The colour of the larvae varies among species.
Most of these beetles, both larvae and adults, are carnivorous predators, primarily targeting barnacle insects and aphids. Some also include fungi in their diets. Consequently, upon hatching, the larvae immediately seek out food. In cases of food scarcity, cannibalism may occur, with eggs, larvae or pupae serving as substitutes for survival. Some other species rely on nectar as a food source. Other than aphids, they prey on various insects, such as flour lice, thrips, mites and psyllidae. Moreover, they also consume small larvae, insect eggs and phytophagous ticks. This versatility makes them valuable predatory insects, especially in the agricultural sector.
Coccinellids are highly valued as primary biological control agents in agriculture due to their ability to prey on crop pests. One notable example is Cryptolaemus montrouzieri, which was introduced to California by Albert Koebele in 1891 to control citrus mealybug, Planococcus citri (Bartlett, 1978). It was subsequently widely adopted as a biological control agent and has been introduced in up to 64 countries to combat 16 or more species of pests. In India, C. montrouzieri was employed in coffee plantations, vineyards and orchards, whereas in places like New Delhi, Azerbaijan and Italy, it is used for pest control because of its ease of maintenance. Another success story was the introduction of the multicoloured Asian ladybeetle, Harmonia axyridis, into Western Europe in the late 1990s to control aphid populations in apple orchards (Axel et al., 2013).
Coccinellids are drawn to crops such as wheat, sorghum, sweet corn, alfalfa, soybeans, beans, cotton, potatoes, mustard crops, tomatoes, asparagus and apples because these provide habitats for aphids which are their primary food source. During cold conditions in winter, coccinellids seek refuge beneath the leaves. The larvae exhibit positive phototropism and negative geotropism, which means that they are naturally inclined to move towards light and away from gravity. This behaviour encourages the larvae to ascend to the tops of plants where aphids are typically found.
Coccinellids are also used in paddy fields where they are prevalent at every stage of rice growth, with some specialising in preying on rice pests such as brown planthoppers and rice stem borers. Coccinellids also target other pests like whiteflies, with over 50 coccinellid species consuming whitefly eggs. Scale insects are another food source for coccinellids, and several coccinellids, including Rhyzobius forestieri, Nephus reunion, Chilocorus nigritus and Chilocorus kuwanae, are employed as biological control agents to combat scale insects.
The use of coccinellids in Malaysia has received limited attention, primarily because coccinellids are perceived as pests. Many farmers still rely on chemical pesticides for pest control, and there is a lack of research on the potential of coccinellids as biological control agents. Therefore, the Malaysian Agricultural Research and Development Institute (MARDI), through the Biological Control Programme, the Agrobiodiversity and Environment Research Centre is actively conducting studies on the use of biological control agents through an Integrated Pest Management (IPM) and ecological engineering approach. In Thailand, the use of coccinellids has seen greater adoption. These beneficial insects are bred on a large scale to combat aphids and other pests. The Department of Agricultural Extension (DOAE) in Thailand has developed breeding facilities and provides ladybirds to farmers for release on their farms.
Unfortunately, the in-situ conservation of coccinellids is not emphasised in agricultural areas. Although these species are not currently listed as endangered on the IUCN Red List, early preventive measures should be prioritised. Environmental activists have suggested several strategies for insect conservation, including educational programmes, habitat preservation and preventing the spread of invasive species. To specifically preserve coccinellids, actions such as providing winter shelter and protecting them from pesticides in and around crop areas are crucial, as these insects are highly vulnerable to insecticides. Diversifying food sources, including aphids and nectar, can also increase the coccinellid population.
In conclusion, the diversity of insect species is a blessing from nature. Some are pests, while others help balance insect populations. It is our responsibility as humans to conserve this natural treasure so that it continues to be sustainable and used in the best possible way.
