Unesp researchers find new pest in Pine production

The plantings of Pinus in Brazil they occupy an area of ​​1,9 million hectares, according to the 2023 report by Ibá (Brazilian Tree Industry), the association responsible for the institutional representation of the planted tree production chain. It is the second most planted forest species in the country, behind eucalyptus.

Due to the great economic relevance of Pinus, the recent discovery of a new pest that has been attacking plantations in the State of São Paulo, generating significant losses and with a real risk of spreading to other areas, raised a warning signal in the forestry sector.

Denominated Sirex obesus, the new pest is a species of wood wasp originating from the southern United States and Mexico, and was detected and identified in Brazil by the team led by professor Carlos Frederico Wilcken, from the Department of Plant Protection at the Faculty of Agricultural Sciences (FCA ) from Unesp, Botucatu campus.

The new wood wasp has the potential to cause various damages to Pinus trees, including death, which results from the action of the pathogenic fungus Amylostereum areolatum, inoculated when the female insect lays her eggs on the tree trunk. The fungus grows inside the trunk, killing the tree's cells and blocking the tracheids, the channels through which the sap circulates. The tree dies after 3 or 4 months of the insect attack.

While the fungus acts, the pest larvae feed on the wood, creating channels or galleries that reach both the heartwood (the innermost part of the trunk) and the sapwood (the outer, youngest and most functional part of woody plants). When the adult insects emerge, they make exit holes in the wood. Attacked trees may also present stains on the wood, caused by the main fungus or other secondary fungi. Therefore, even if the affected tree does not die, the damage caused by the pest makes commercial use of the wood unviable.

The presence of the pest has already been confirmed in 16 municipalities in São Paulo, including Itararé, on the border with Paraná, the main pine producing state in Brazil. The researchers consider the risk of this new species of wood wasp to disperse to the neighboring state and to the southern region in general, where more than 80% of the species' plantations are concentrated, to be very high. And there is still the risk of Sirex obesus reach other Mercosur countries, such as Argentina, Chile and Uruguay, which are also important Pine producers.

The Ministry of Agriculture and Livestock has already been notified of the existence of the pest and the Forest Protection Program (Protef), a nationwide program related to forest pests and linked to IPEF (Institute of Forest Research and Studies), an entity that integrates companies, universities and research institutions focused on the forestry sector, has already issued a statement written by Professor Wilcken, warning about the identification of the insect.

knowing the enemy

Companies and producers in the forestry sector are already quite familiar with another species of wood wasp, related to the Sirex obesus. Named sirex noctilio It is considered the main pest to attack Pinus. The insect originates from the Mediterranean region (southern Europe, Middle East and North Africa) and its presence in the states of São Paulo and Minas Gerais and the southern region of the country has been known since 1988.

The pest has already caused many losses to Brazilian production, especially in southern Brazil during the 1990s, notably with the mortality of trees of the P.taeda species, widely used in cellulose manufacturing and the furniture industry. “Today, there are already well-defined monitoring and biological control procedures for its occurrence. There are currently records of its presence in nine countries as an exotic or invasive pest. And until now, there was no record of other species of Sirex occurring in Pine plantations around the world”, reports Professor Wilcken.

In November 2023, during a field visit to a Pinus production farm in Buri/SP, the professor found trees with resin splashes on the trunk, which indicate that eggs had been laid there, and with circular holes typical of the emergence of adult insects. The property houses plantations of Pinus hybrids used in resin production. There were plantations with high wood wasp infestation and mortality reached approximately 50% of trees. During this visit, live larvae of different sizes, pupae, newly formed adult males and females were collected and unequivocal morphological differences were found in relation to the already known sirex noctilio.

The adult individuals were taken to the Biological Control Laboratory of Forest Pests at FCA/Unesp. Subjected to mitochondrial DNA analysis, samples were also sent to the team of taxonomist Nathan Schiff, from the United States Forest Service (Forest Service), an agency of the United States Department of Agriculture (USDA) who confirmed, using morphological and molecular characters, are of the species Sirex obesus.

According to Professor Wilcken, identification was difficult because, as it is a natural species in the southern United States and Mexico, it is controlled there by its natural predators, not causing major problems for the trees. “Because it does not attract attention or cause any problems, the species is little studied. Therefore, there is no complete information about its cycle and which species of eucalyptus it attacks, but apparently the insect has more than one generation per year, while with S. noctilio it is already known that new adults emerge only once a year. ”.

Another distinction between wasp species is that the S. obesus seems to have no preference for pinus taeda. “In the areas we looked at, S. obesus It attacked tropical species and hybrids developed for resin production with greater intensity. At the detection location, there is a small batch of P. taeda where the insect is present, but the infestation is lower than in hybrid areas”, says Wilcken. “However, if the plague reaches the southern region, the tendency is for it to adapt over time and attack more and more pinus taeda, the most planted species in the region.” To date, only one species of pine, called Pinus elliottiis did not suffer from infestations, appearing to have some type of resistance to the pest.

Plague impacts

In addition to the southern region, Pinus is widely planted in the states of São Paulo and Minas Gerais. Production in the South is mainly focused on the manufacture of furniture, taking advantage of the lightness and resistance of wood. Part of the production is also used in the cellulose industry.

In São Paulo, the largest production is focused on the production of resin, which will be used in the chemical industry. Solvents in the paint industries use Pine resin as a raw material. The best quality resin is also used in the pharmaceutical and cosmetics industry. All of these segments can suffer from the consequences of the pest and resin production is the one that is most immediately at risk.

Resin extraction increases the predisposition for attack by S. obesus. Resin is the tree's defense. It emerges from the trunk when the insect oviposites, thus expelling the eggs and the pathogenic fungus. The resining activity stresses the trees which, in this case, produce less resin, which makes them more susceptible to wasp oviposition. “From what we estimate so far, there can be 200 to 300 insects in a single Pine trunk. Any factor that stresses the tree helps make it more susceptible. Climate change, with more heat and lower-than-expected rainfall in the state of São Paulo, may have contributed to stressing the trees, creating a favorable scenario for the insect.”

Pine wood is also the most used in the production of "pallets", used for crates when transporting products. “This is an area that could be affected if there is a restriction on the use of Pine pallets in products exported by Brazil. Changing treatment methods or replacing the wood in pallets with eucalyptus can increase the cost of exports and make Brazilian products less competitive.”

Pest management

With the science from the Ministry of Agriculture and the alert issued to the entire forestry sector, research must advance and determine the real extent of the problem in the country, as well as the best strategies for managing and controlling the pest. But there is already certainty that monitoring of plantations must be intensified, since the damage caused by S. obesus appear to be more intense and the adult emergence period longer than S. noctilio.

As in the case of S. noctilio Chemical control does not work to combat this species of wood wasp. Insects grow and develop inside the trunk, which makes insecticide applications harmless. Researchers start from what is done with S. noctilio to determine possible forms of management for S. obesus.

Silvicultural control, with thinning in plantations, is a first measure. Thinning consists of removing specific trees from a plantation with the aim of generating greater growth in the remaining trees. Thinning, therefore, tends to make trees more resistant and healthy and, in theory, less susceptible to insect attacks. However, this technique loses efficiency in Pine plantations for resin production, since the resin itself will already stress the trees.

The other form of management is biological control, with the application of the parasitic nematode Deladenus siricidicola, a microscopic worm created in the laboratory released every year by companies and forestry producers in the southern region of Brazil to combat S. noctilio. “The nematode feeds on the phytopathogenic fungus Amylostereum areolatum inside the wood and, when it finds the insect larvae, it passes into the parasitic phase, penetrating the larvae and causing the sterilization of the adult females. From then on, the nematodes lodge in the eggs and are dispersed in the Pine plantations by the females themselves, through the eggs.”

However, there are doubts whether the nematode will be able to parasitize larvae of S. obesus how do you do with S. noctilio. Research on nematodes is being conducted by professor Silvia Renata Siciliano Wilcken, from the Department of Plant Protection at FCA/Unesp. The results, although still preliminary, are worrying. “To date, the presence of the nematode D. siricidicola in larvae, pupae and adults of S. obesus, with more than 500 dissected individuals”, says Professor Wilcken. “If these nematodes are not in fact effective, we will have to try to use other nematodes, but to do this we will have to prospect, probably among the Pine forests in the United States, the area where the pest originates.”

Likewise, Professor Edson Luiz Furtado's team, from the Department of Plant Protection at FCA, has already discovered that the fungal pathogen transmitted by S. obesus is different from that transmitted by S. noctilio. It is Amylostereum chaeilletii and it is not yet known whether the nematode can feed on it.

There is also another form of biological control that occurs through the action of microwasps Ibalia leucospoides, which parasitizes eggs and young larvae, and Megarrhysa nortoni, which parasitizes larger larvae. “They are naturally occurring insects, difficult to create in the laboratory so that we can release them on crops. We are working with them, but it still takes time for them to be efficient alternatives.”

For Professor Wilcken, the possible consequences for the damage caused by this new species of wood wasp are many and the only path to be taken now is to develop public policies on the topic, with integration of actions. “It’s a problem that can affect more than one sector of the economy. It is now necessary to involve the ministry and state agricultural defense agencies, in addition to companies in the forestry sector, to have a complete survey, at a national level, of the size of the problem. It will be necessary to carry out clarification campaigns, while scientists seek to provide the necessary support in terms of research.”