Control of Diabrotica speciosa

Corn is one of the main crops in Brazil and the world, as in addition to being a great source of nutrients, it is also a source of raw material in the manufacture of by-products in large areas such as chemistry, pharmaceuticals, food, beverages and fuels.

The most significant part of corn cultivation is found in the area of ​​animal nutrition, with a share of 70% of all world production. In Brazil this number varies from 60 to 80%. The remainder is divided between human consumption, fuels and pharmaceuticals.

At the beginning of its cultivation, corn was only used for human subsistence, over the years it gained great importance and strength for poultry and pork production as a nutritional implementation.

Corn is attacked by several pests, approximately 20 species, including the fall armyworm, some species of hemiptera, screwworm and Diabrotica, better known as cowworm, all of which have great potential to cause enormous damage.

Knowing Diabrotica speciosa

Diabrotica speciosa, also known as vaquinha, green vaquinha, patriotic vaquinha or pin larva (whose name arose from the association of its damage to potatoes being similar to pin holes) is a species of beetle (coleoptera) with a polyphagous habit, and can feed of different crops such as corn, tomatoes, potatoes, beans, soybeans, sunflowers, eggplants, cabbage, pumpkins, strawberries, peppers, among others.

The adult is around 4,5 to 6 mm. There is sexual dimorphism: the male is smaller than the female. They are green in color with three yellow spots on each elytra, the basal spot being longer and reddish. They have dark antennae and a head ranging from brown to black. Females generally oviposit around the roots of plants, preferring soils with high drainage and generally dark in color, due to the amount of organic matter on top, maintaining ideal conditions for the survival of eggs and larvae at temperatures around 25°C. degrees and 65% humidity. They can lay up to 2000 eggs in their life cycle.

The eggs are yellow and measure around 0,5mm in diameter and the incubation period is approximately seven days.

The larvae measure around 10 mm in length and are whitish to yellowish in color, with a black head, thorax and legs. They have three larval instars, low mobility and do not have the habit of excavating galleries, hence their preference for well-drained and loose soils. They live around 10cm above the soil surface, around the roots and go a few centimeters deeper in times of extreme frost.

The pupae are around 5 mm long, white and are protected in a pupal chamber below the surface of the soil.

Diabrotica specicosa It has a cycle of 24 to 40 days, and this insect is very susceptible to climate changes and temperature variations, which can alter its cycle. There can be five to six generations per year and they do not have diapause in winter.

The quality and quantity of food consumed also affects the insect's cycle in the larval phase in relation to growth rate, development time, body weight, survival, fecundity, longevity, movement, competition capacity and when it does not consume adequate food when transforming. in pupae it forms fragile adults, with restricted movement and food. In adulthood, the availability of nutrients available in the food consumed influences behavior, survival and reproduction, directly affecting its biological cycle.

Due to the female's egg laying efficiency, an uncontrolled infestation can occur quickly when not monitored effectively.

Diabrotica Damage

This insect pest has great economic importance, since from the larval stage to the adult stage, it is capable of causing damage and losses to crops, from germination to harvest. They are capable of attacking seeds, roots, shoots, leaves, fruits, pollen and can even serve as vectors of bacterial diseases and virologies. According to some studies, an infestation of two individuals per plant can cause crop losses of 50% to 70%.

Adults feed on the leaves causing scraping, damage that often resembles fall armyworm damage and is easily confused. They cause extensive defoliation in plants, damaging the active photosynthetic area, significantly reducing the production of photoassimilates for the plant, influencing leaf growth and development, resulting in loss of productivity and profitability.

The larvae generally have the habit of causing damage to reboleiras, feeding on the roots, causing nutritional and water deficiency, as well as support problems, causing lodging and “gooseneck”, so called due to the curved appearance that the crop has, also decreasing the plant's performance, making it weak and susceptible to diseases. They can also feed on the seeds, making them unviable, leading to planting failures.

chemical control

There are several insecticides registered with the Ministry of Agriculture to control Diabrotica sp. in the larval and adult insect stages. However, to have good efficiency in controlling this pest in the larval stage, the product must have active ingredients with high persistence in the soil for between 6 and 10 weeks.

Granulated or sprayed insecticides in the planting furrow have shown great promise in controlling this pest in the larval stage, especially in direct planting techniques.

Despite being very promising, granulated insecticides have less availability of suitable equipment for their application, greater risks of poisoning and higher costs.

Seed treatment techniques in corn for this pest are not very effective, as the larvae can cause damage to this crop within two months after sowing and the insecticides do not have sufficient residuals to protect the root system during this period.

Cultural control

Proper management of the area is always the best alternative, as is effective and constant monitoring and it is always important to also carry out an analysis of the area's history and incidence of pests.

The use of resistant cultivars is rarely recommended and used for this pest in corn crops. There are cultivars resistant to other diabrotic species in culture, but none specifically to specious. Resistant cultivars have a more developed root system or emit new roots that better withstand the attack, preventing the death of the seedling.

For the cultural control of this pest, a technique called “trap culture” is widely used, where lines of other crops considered more “attractive” than corn in terms of nutrition are planted (e.g.: beans, pumpkin) so that they do not attack the focus crop, in this case corn.

Biological control

When biological control is used, as the name suggests, beneficial insects are used and preserved in the crop, as biological agents are specific to the host.

The biological control tactic is very promising for controlling this pest, as there are several natural enemies in nature, such as some species of spiders and cell flies. Other used and promising techniques to control this insect are fungi, Beauveria basiana e  Metarhikum anisopliae. However, when Diabrotica sp. It ingests some species of plants from the curcubitaceae family (melon, zucchini, strawberry, watermelon, cucumber), and is not parasitized. In these cultures there is a substance called curubitacin, ingested by the coleoptera, which is toxic to many of these natural predators.

Another technique used is pheromone traps, which attract males to pet bottles spread across the field, containing water and detergent.

Due to the habit of this pest to be polyphagous and the great viability and oviposition capacity of the female during its lifetime, good monitoring of the culture is extremely important, with monitoring and use of effective techniques to control infestations, as they can spread. easily in any culture.

By Karen Helena de Andrade Rodrigues, pest management specialist

Article published in issue 292 of Cultivar Grandes Culturas Magazine