The banded pine weevil, Pissodes castaneus (De Geer, 1775) (Coleoptera, Curculionidae), is an important pest of Pinus (Pinaceae) in South America (Iede et al. 2004). It was detected in Brazil in 2001 in the county of São José dos Ausentes, Rio Grande do Sul, on Pinus taeda L and later it was detected in the states of Santa Catarina and Paraná (Iede et al. 2004). In 2002, 7.6% of the trees of a plantation of P. taeda grown in Cambará do Sul, Rio Grande do Sul, were attacked by P. castaneus while in São Joaquim, Santa Catarina, 16.5% of the trees were attacked (Iede et al. 2004).
This insect represents a threat to Brazilian forest production, as it has the potential to cause economic losses, such as those that occurred in Uruguay where there was a mortality rate higher than 10% (Grez et al. 2000). More than 50% of trees in a stand can be attacked in one year (Cadahia et al. 1992).
Conifers are long lived gymnosperms, which includes many species that successfully inhabit large areas of our planet. As raw material for many products (wood, paper, plastic, fuel, and many chemicals), their economic impact on our society is of great importance. In European countries such as Sweden, 83% of the forests consist of conifers, mainly Norway spruce (Picea abies L.) and Scots pine (Pinus sylvestris L.) (Alin and Sundberg 2003). In South America, specifically in Brazil, pine trees, mainly P. taeda and Pinus elliottii Engelm., have been planted on commercial scale for over 30 years (Ahrens 2000). Currently, there are about 2 million hectares of reforested pine plantations, in large continuous areas and generally in narrow genetic base stands, mainly in the South and Southeast regions (Iede et al. 2004). The product of these plantations is destined mostly to the timber and cellulose industries (Cardoso and Lázzari 2003).
Insects use volatiles as their major method to find food, mates or an appropriate site to lay their eggs (El-Shafie and Faleiro 2017). For plants, which cannot escape threats, chemical constituents play an important role in their defense system. Their response to feeding or oviposition of herbivorous insects can be direct, by feeding deterrents, impairing digestion or producing toxins (Kessler and Baldwin 2002), or indirect, by the release of volatiles which attract natural enemies of the herbivorous insects (Dicke and van Loon 2000; Arimura and Pearse 2017).
However, there are cases that the induced compounds may act as kairomones (Nordlund and Lewis 1976; Keeling Christopher et al. 2006; Lusebrink et al. 2016; McCormick et al. 2016), i.e. chemical compounds emitted by an organism that induce a benefic response to the receiving organism from another species, or have a synergistic effect with insect pheromones – compounds used in intraspecific communication –, as happens with Pinus ponderosa when damaged by Dendroctonus brevicomis Lec. (Bedard et al. 1969).
Conifers can use a large array of structurally diverse mono-, sesqui- and diterpenoids as a chemical defense against herbivores (Lewinsohn et al. 1991; Phillips and Croteau 1999; Trapp and Croteau 2001; Martin et al. 2002, 2003). Induction of volatiles terpenoids may result in a quantitative or qualitative difference in the chemical profile produced by a plant (Fitzgerald 2003). The herbivore-induced change in the plant volatiles can be specific for the plant and herbivore species, the plant age and the herbivore stage (Takabayashi et al. 1994; De Moraes et al. 1998).
Defense responses of induced terpenoid have been intensively studied using spruce (Picea spp.) as model plant. Anatomical defenses like traumatic resin duct formation or polyphenolic parenchyma cell activation are induced by wounding or by attacking insects and pathogens (Tomlin et al. 1998; Nagy et al. 2000; Franceschi et al. 2002; McKay et al. 2003). Besides, induction of terpenoids have been observed in spruce after mechanical wounding or treatment with methyl jasmonate, a plant hormone known to upregulate plant defenses (Nault and Alfaro 2001; Martin et al. 2002; Faldt et al. 2003).
These terpenoids can act as repellents or toxins against those herbivores, defending conifers directly, or mimic juvenile hormones (Lewinsohn et al. 1991; Langenheim 2003; Mumm et al. 2004). Likewise, conifer volatiles can also attract predatory and parasitic insects, consequently defending conifers indirectly against herbivores (Nadir and Raffa 2001; Mumm et al. 2003; Sullivan and Berisford 2004; Hilker et al. 2005).
In previously studies it was described that P. castaneus adults were attracted to the volatiles emitted by P. taeda (Marques et al. 2012) and previously stressed plants showed a higher infestation (Iede et al. 2004). In the present study, we conducted detailed GC–MS analyses of volatiles emitted by twigs of P. taeda, both healthy and attacked. We analyzed how the attack by P. castaneus males and females affects the volatile pattern emitted by P. taeda twigs. We also carried out laboratory and field assays to evaluate the attraction of P. castaneus to healthy and stressed host plants.