Knowledge and management of the root spittlebug Mahanarva fimbriolata

Sugarcane is the most important crop in Brazil, being responsible for the greatest development of agribusiness in the country involving ethanol and energy, with around 8,6 million hectares of harvested area, however its development and potential is threatened by several pests that cause great commercial losses.

The root spittlebug (Mahanarva fimbriolata) is one of the pests that threaten this crop, causing reductions in the quality of raw materials, which can reach up to 30%, can cause contamination in industrial processes and result in losses in productivity, which vary from 15% to 85%. Therefore, it is extremely important to know about the insect pest, pay attention and be careful with monitoring so that assertive decisions can be made in combating and controlling it in the crop.

Getting to know the pest insect

The root spittlebug (Mahanarva fimbriolata) belongs to the order of Hemiptera (as well as cicadas, bedbugs and aphids). It is a sucking insect.

Its biological cycle varies from 63 to 79 days, and is strongly affected by climatic factors that directly interfere with the insect's population dynamics, hindering their survival and affecting the females' reproductive cycle. The beginning of its cycle is closely associated with the "rainy season" where the humid climate favors the hatching of eggs and protection of nymphs with "foam".

The leafhopper goes through three biological stages during its development: egg, nymph and adult.

Females lay their eggs at the base of clumps or among plant debris left on the ground. The ban on burning sugarcane encouraged infestation due to the overlapping of straw in the field and the increase in unwanted weeds. The use of fire techniques in sugarcane fields controlled the pest's population growth by destroying all biological forms of the insect.

Each female lays an average of 340 eggs during her life cycle, with an incubation period of approximately 15 to 20 days. However, with the decrease in rainfall, the eggs undergo diapause, where they enter a period of dormancy, ensuring their survival for hatching in favorable conditions, giving rise to first-stage nymphs (ecdysis).

Nymphs are considered radiculoids because they spend their entire development period feeding on the root system. They attach themselves to the roots of the cane or rootlets and remain for around 30-40 days covered by a whitish foam similar to soap foam, which they produce as a form of protection against exposure to the environment, predators and climate, also making it difficult for control products to come into contact with the insect. During this period, the nymphs go through 5 changes of ecdysis until they mature into the adult phase.

The female lives on average 22 days and the male around 17 days. They are between 11 and 13 mm long, with females being larger than males. Males are reddish in color with spots on their wings and have longitudinal black stripes on their bodies, with the female having a more brownish color.

In the adult phase, insects have more developed legs and are adapted for jumping, which facilitates their movement. They also have wings, but they are less adapted and are more common for dispersion over short distances. Thus, they are able to move from the roots to the aerial parts of the plants, where they begin to feed and cause economic losses to the crop.

Economic damage

The economic damage caused by this pest to the crop can be direct or indirect. Direct damage occurs when the stalk withers, tiller death, shortening of internodes and non-viability of lateral buds result in a loss in the percentage of tons per hectare (T/H). Indirect damage affects the quality of the final product, interfering with the purity of the juice, color of the sugar, contaminants in the process, increased fiber and sucrose content (quality of the raw material).

The attack of this insect causes significant losses in the sugarcane field itself, but its greatest economic loss is in productivity, since with the addition of plant fiber and dead dry stalks, the industry demands greater costs and difficulty in milling. The increase in contaminants and phenolic compounds interferes with the consumption of yeast in fermentation, impacting the production of ethanol, and can also affect the characteristics and purity of the final sugar.

The first economic damage caused by the leafhopper begins in the nymph phase when they feed and introduce their mouthparts through the sugarcane epidermis where they reach the woody vessels. The insect's saliva contains enzymes that aid in its digestion, but when inserted into the plant it causes necrosis of the root tissues, which hinders or prevents the flow of water and nutrients from the conducting vessels (phloem and xylem) to the aerial part of the plant, causing its death due to nutrient imbalance and dehydration.

This fact is noticeable because it causes the characteristic effect of “sagging” and thinning of the stalks, subsequently causing cracks and wrinkles, opening the door for more pathogens to enter; the stalks often end up becoming hollow inside.

In the adult phase, the insect feeds on the leaves and causes “sugar cane burning” due to the toxin injected when feeding, causing yellowish spots that turn red over time, significantly reducing the photosynthetic capacity of the plant until they become opaque and die, also causing yellowish streaks on the leaf blade.

Identifying the pest in the field

Identifying leafhoppers in the field is simple. Visually, the most common symptoms that can be noticed are: yellowish streaks on the leaf blade, curled edges and wilting of the stem. However, it is still necessary to monitor the crop, as these symptoms can easily be confused with symptoms of other pests, diseases or even nutritional deficiencies.

To confirm the presence of a leafhopper infestation, monitoring is carried out along the sugarcane lines, under the straw and at the base of the clumps in order to identify the presence of the whitish foam produced by the nymphs.

control methods

The main means of control is knowledge of the insect pest and careful monitoring to assess the stage of the infestation, monitoring the evolution of the pest.

Sugarcane field monitoring should occur mainly during rainy periods, when the insect begins to develop, and action must be taken when the “control level” (CL) is reached, with 5 nymphs/meter and 0,5 to 0,75 adults/cane being identified.

When it reaches 10/nymphs/Linear Meter it is called (NDE) where the pest has reached an “economic level” damage potential.

These calculations are based on the monitoring area, not the total area planted with the crop.

Sugarcane species with a high sugar content are more likely to be infested by leafhoppers, and monitoring care should be redoubled in the initial phase.

As with any crop and for any pest, integrated pest management is always the best solution because when you integrate several types of control you increase your treatment effectiveness rate.

For effective control of leafhoppers, physical, chemical and biological methods are known in order to find the most effective method for control.

physical control

The physical cultural method is extremely important in combating leafhoppers due to the pest's exposure to unfavorable environments.

One of the most commonly used techniques is to remove residual straw, leaving the soil exposed, increasing the temperature of the area and reducing humidity, thus making it difficult for eggs and nymphs to survive and hatch. This technique is around 70% effective in the initial phase and is not recommended as the only form of control for severely affected areas. However, a disadvantage of using this technique is that it reduces soil humidity due to sun exposure without the use of cover, which can influence and harm the development of early sprouting of ratoons. This is an important point to be evaluated when choosing this technique between cost and benefit.

Other widely used methods include investing in planting species genetically modified to the gene of this pest, not carrying out direct planting and keeping the soil exposed during planting, investing in crop nutrition with liming, fertilization and phosphating processes, favoring root growth, making it less fragile and improving its resistance to lack of water and pest control.

chemical control

The chemical method is highly effective in controlling leafhoppers, especially systemic ones. However, in some cases, reapplication is necessary, requiring two or three passes due to insect mutation and resistance to some insecticides.

Chemical control should be applied at the beginning of the pest infestation because the population density of the insect pest is lower and its distribution is localized, thus increasing the efficiency of the product in controlling the disease and minimizing the difficulty of application when carried out in early-stage sugarcane. When the infestation reaches the level of damage, it is recommended to start application as soon as possible, as the product will respond better to the effectiveness of the treatment.

In some cases, nymph and adult control require different products to be controlled. To control nymphs, granulated spray products should be used, and in the adult phase, it is recommended to apply more selective insecticides so that they do not also kill natural enemies present in the area.

Chemical control, like any method, has some disadvantages such as: high application cost, adequate atmospheric conditions required for application, resurgence of biological phases of the insect as it does not reach all phases at once, imbalance in the ecosystem with the death of natural enemies, resurgence of the pest resistant to the compound used.

There are numerous products registered on the market today for controlling leafhoppers and new products are emerging every day. Therefore, the tendency is that the greater the number of products with different compounds and active ingredients that appear on the market, the greater the effectiveness of the action to control the pest.

Due to the diversity of products on the market, it is possible to rotate products and larger compounds, meaning that old products can once again have great results in terms of effectiveness due to the low resistance of insects to them.

Products are appearing on the market that promise shock-based effects with low solubility and that act immediately on the insect through ingestion and contact with a lasting effect, controlling all living phases of the insect and still being selective.

Biological control

Biological control has been growing more and more in the market as a way of protecting the environment without excessive use of pesticides, damaging the ecosystem and without grace periods.

One of the techniques for biological control of the leafhopper is the introduction of natural enemies into the field, where there are several species that perform this role, especially egg parasitoids. Anagrus urichi e Acmopolynema hervali, the nymph predator fly Salpingogaster nigra, the fungi Metarhikum anisopliae (being effective for all living forms of the pest) and Batkoa apiculata normally used for adult control.

The parasitoid Anagrus urichi is an egg parasite, the technique is already widely used and has significant effectiveness for controlling the leafhopper in pastures, and is currently being studied extensively for sugarcane leafhoppers, where it shows very favorable results. Another leafhopper egg parasite is the Acmopolynema hervali It is a microhymenopteran with registered control efficacy for sugarcane leafhoppers.

The fly S. Nigra It acts as a predator of nymphs; the larvae of this fly penetrate the whitish foam and feed on the leafhopper nymphs at the base of the clumps. Its production is very advantageous, as it has a high rate of reproduction and fertilization, with short cycles that can have two to three generations of the predator per cycle of the insect pest. Its predation rate is very high, and it can feed on the nymphs that grow along the radicchio roots or that are deeper in the soil, which products would not be able to reach.

the fungus Batkoa apiculata It usually acts on adult insects. Its infestation in the insect pest occurs through the joints of the legs, cracks in their shells or gaps in their tissues, where the spores penetrate and begin to multiply. As soon as the fungus colonizes and the spores begin to multiply, the insect becomes paralyzed, losing its motor ability, ability to move or feed. The spores cover the entire body of the insect, occasionally leading to its death, known as “powder death”.

Studies report that this fungus is capable of controlling even enzootic-level infestations, which are infestations that, even in low quantities, are always present in that area and are recurrent.

Finally, the best-known and most widely used method today is the application of entomopathogenic fungus. Metarhikum anisopliae Because the use of the technique is economical and sustainable, it has great potential for effective control. Also known as green fungus, the fungus, when in contact with the insect pest, germinates the conidia, which penetrate the insect's tegument through mechanical-enzymatic action in a period of two to three days. The colonization period lasts from two to four days. At this stage, the insect no longer causes damage to the crop and becomes completely paralyzed. Sporulation occurs in two to three days, depending on environmental conditions, so the fungus begins to attack more insects. The total disease cycle is eight to ten days for the death of the insect and infestation of the fungus.

When the insect pest is affected, it begins to show white mycelial growth on its body, followed by green sporulations, thus called green fungus.

When this method with the fungus Metarhikum anisopliae When applied correctly, considering ideal environmental conditions, the quality of the fungus and the dosage, the method becomes very efficient, reducing infestation in the field by up to 75%. It is generally applied at the beginning of the infestation when only one live form of the insect is found per linear meter, and is reapplied if necessary. The fungus can be applied using ground-based mechanisms with tractor-mounted or aerial equipment.

Using integrated pest management to effectively control insects in your crop is always the best option, adopting control measures according to your monitoring and current reality, being extremely assertive in decision-making.

By Karen Helena Rodrigues, specialist in agricultural pest management

Article published in issue 298 of Cultivar Grandes Culturas Magazine