Basil oil has potential to control caterpillars

The traditional broadleaf basil (Ocimum basilicum L.), also known as basilicão or alfavaca, can become the basis of a natural product for controlling important crop pests. By applying the essential oil of this plant to bean leaves, scientists from Embrapa Environment (SP) recorded the death of around half of the caterpillars of the species Helicoverpa armigera and a case fatality rate of 30% for Anticarsia gemmatalis. The first was introduced in Brazil in 2013 and is known for its great voracity and A. gemmatalis it is called the soybean caterpillar because it is the main pest of the legume. Both attack several crops and, therefore, are considered important agricultural pests.

Basilicão was the most effective among the nine plants whose essential oils were tested in controlling the two caterpillars in the research (look picture). One of the motivations for using oils is their low, or even no, toxicity to the environment and agricultural crops. The scientists carried out biological and behavioral assessments of the insects and identified the main compounds present in the oils. Part of the results were published in a research bulletin.

The researchers consider this study promising, and it complements scientific work carried out with other essential oils, such as Neen oil (azadiract indica), widely used in pest control. Another important factor is the possibility of reducing the use of chemical pesticides, which can be done through substitution or the use of integrated pest management (IPM). Reducing the use of chemical insecticides also helps reduce insect resistance to these pesticides, a problem that has been growing in crops. “These oils can also become another insect control tool in organic agriculture, in which these compounds are permitted, expanding the range of pest management possibilities”, says the Embrapa researcher Jeanne Marinho Prado.

A voracious caterpillar With great dispersal capacity and a larval stage with a highly polyphagous habit (capable of feeding on more than 60 families of plants), the Helicoverpa armigera It is now widely distributed throughout the country and mainly attacks soybean, corn, beans and cotton crops.

A voracious caterpillar

With great dispersal capacity and a larval stage with a highly polyphagous habit (capable of feeding on more than 60 families of plants), the Helicoverpa armigera It is now widely distributed throughout the country and mainly attacks soybean, corn, beans and cotton crops. 

Prado explains that the use of insecticides can promote the resistance of pest insect populations. The lack of new insecticide molecules and the repeated use of products with a similar mode of action in the same season can favor the resistance of the insect population, reducing the effectiveness of the applications.

In addition, there is a growing concern of consumers and producers with the health of workers and with the contamination of food and the environment, generally highlighting the demand for more natural ways to offer protection to plants against insect attack. 

The researcher reports that the essential oils of basilicon and thyme were the ones that showed the greatest bioactivity on caterpillars and pupae of A. gemmatalis, in biological and behavioral aspects. In the adult stage, A. gemmatalis was most affected by the essential oils of sweet orange, tea tree and oregano, accompanied by the essential oils of citronella and ginger, the latter being responsible for making all the eggs deposited unviable. Thyme and mint essential oils have not been evaluated in the reproductive phase. In the tests on caterpillars H. armigera the treatments with essential oils of basilica, cinnamon and tea tree stood out, but no treatment altered the foliar consumption of the caterpillars. 

50% lethality

In tests on caterpillars H. armigera treatments with essential oils of basilica, cinnamon and melaleuca promoted, in ten days, the death of half of the evaluated caterpillars. However, none of the oils harmed the feeding of the caterpillars.

Among the treatments evaluated on the species A. gemmatalis, basilicum and thyme essential oils caused the highest mortalities observed in caterpillars and pupae. The others caused mortality lower than 14%, and tea tree and ginger oils were equal to the control treatment, with no case of mortality among the evaluated insects.

With the exception of cinnamon, ginger and sweet orange essential oils, all others caused a reduction in larval weight gain of A. gemmatalis in relation to the control-treatment caterpillars, with the best results obtained with basilica, oregano and thyme. Thyme essential oil was the only one to cause a reduction in pupae weight. 

The tested oils Essential oils are complex mixtures of lipophilic volatile substances, generally odoriferous and liquid, with volatility being their main characteristic. They are natural substances from medicinal, aromatic and condiment plants, often easy to obtain at low cost and without residual toxicity, and can be a good option for pest control, as, for the most part, they are systemic, easily degraded and little or non-phytotoxic. Sweet orange oils (Citrus aurantium sweet), ginger (Zingiber officinaleRoscoe), melaleuca (Melaleuca alternifolia), cassia cinnamon (Cinnamommum cassia), citronella (Cymbopogon sp.), mint (Mentha arvensis), oregano (Origanum vulgare), thyme (Thymus vulgaris) and basilicon (Ocimum basilicum L.)

The tested oils

Essential oils are complex mixtures of lipophilic volatile substances, generally odoriferous and liquid, with volatility being their main characteristic. They are natural substances from medicinal, aromatic and condiment plants, often easy to obtain at low cost and without residual toxicity, and can be a good option for pest control, as, for the most part, they are systemic, easily degraded and little or non-phytotoxic.

Sweet orange oils (Citrus aurantium sweet), ginger (Zingiber officinaleRoscoe), melaleuca (Melaleuca alternifolia), cassia cinnamon (Cinnamommum cassia), citronella (Cymbopogon sp.), mint (Mentha arvensis), oregano (Origanum vulgare), thyme (Thymus vulgaris) and basilicon (Ocimum basilicum L.)

Of the essential oils evaluated for the reproductive phase, sweet orange, tea tree and oregano caused a reduction in the number of eggs per female. These same three essential oils also caused a reduction in the viability of eggs, accompanied by the essential oils of citronella and ginger, the latter being responsible for the unfeasibility of all deposited eggs. The lifespan of the caterpillars that reached the adult stage was not influenced by any of the treatments applied to the caterpillars of A. gemmatalis. 

Thyme essential oil caused mortality in the evaluated population of A. gemmatalis and reduction in the weights of caterpillars and pupae. The essential oils of ginger and citronella caused the unfeasibility of all eggs deposited by adults of A. gemmatalis, possibly due to the action of its major compounds. Scientists are now evaluating the lethality of each of the essential oils used in the research to define which ones should continue investing in to search for insecticidal molecules aimed at formulating phytosanitary products that can contribute to integrated pest management.

In addition to Jeanne Marinho Prado, researchers participated in the work Lilia de Morais,  Embrapa Agrobiology, and Ricardo Pazianotto, from Embrapa Environment.

The power of plants

Plants are a great source of molecules, many unknown, which can serve as models for chemical synthesis, generating low-cost, effective and environmentally safe products, which can be standardized, registered, with quality control, aiming at reproducibility and constancy of components. chemicals, and, above all, that meet the needs of producers. 

Compounds derived from plants are potential sources of protection against pests, as they can have a toxic action (which harms the development of insects, which can lead to their death), repellency (which keeps insects away) or deterrence (which harms feeding or reproduction). of insects).