Damage Caused by Tribolium castaneum (Coleoptera: Tenebrionidae) in Stored Brazil nut

. Tribolium castaneum is an insect that occurs worldwide and it is a pest that attacks stored products, in particular, grains and seeds. The adult and immature forms are categorized as secondary pests which feed on grains or seeds previously damage in storage conditions. The objective of this study was to describe the type of damage caused by adults and immature of T. castaneum in Brazil nuts and identify the type of damage caused by Coleoptera. It was also verified whether the shell can protect the almond from the attack of this pest. The lesions inflicted by this insect starts as a scratched surface, which evolves into galleries and even injuries capable of modifying the original shape of the almond. Due to its capacity to promote considerable damage with consequent losses in the value of the nuts, T. castaneum may be listed among pests of Brazil nut categorized as


Introduction
The genus Tribolium includes pests commonly found in storage facilities of grains and seeds and they cause substantial losses in products like cereals, brans, animal's food, flours and others (Trematerra & Sciarretta, 2004;Daglish, 2006).
The species Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) are the most commonly representatives of this genus found in Brazil. Morphologically, they have great similarities, and the separation is basically done by the differences in their antennae and head structures. The last three antennal segments in T. castaneum are distinctly wider and the lateral edge of the head extends to 1/3 of the distance of the eye when laterally observed. On the other hand, T. confusum does not have such pronounced last three antennal segments and the lateral edge of the head extends to 2/3 of the distance of the eye in the lateral view (Pereira & Almeida, 2001).
Tribolium castaneum is popularly known as the beetle of the flour and it is considered a cosmopolitan insect, mainly prevalent in the tropics (Rees, 1996;Faroni & Sousa, 2006). This beetle is categorized as a secondary pest because the adult and immature forms feed on pre-cracked or broken grains, which were damaged by primary pests; however, reports in the literature describe the ability of this insect to survive even in the undamaged grains (White, 1982).
Brazil nut, compared with other products used in human food, has not stood out in the international scientific literature. It may be partly explained due to the regions of its production, restricted mainly to the Amazon Biome (Thomas et al., 2015). However, despite of being produced only in certain areas of South America, its consumption is observed across all the continents (ITC, 2015), and it is an important income source for innumerable families that live by extractive activities (Homma, 2012;Moll-Rocek et al., 2014). The greatest scientific efforts related to Brazil nuts are studied from the perspective of this product as an influence on human health (Gonzales and Salas. 2006;Berno et al., 2010;Colpo et al., 2013).
There are even efforts to understand the relationship of these nuts with the aflatoxigenic fungi (Arrus et al., 2005;Pacheco et al., 2010;Martins et al., 2012). Studies conducted to comprehend the behavior of the Bertholletia excelsa seeds during the pre-processing and industrialization steps are still incipient (Ribeiro et al., 1993;Nogueira et al., 2014;Kluczovski et al., 2015), however, such types of research have emerged due to the current demand for export of a product that fits the laws of importing countries (Álvares et al., 2012).
The efforts of these researchers are raising people involved in the Brazil nut chain awareness, from the forest to the market, and attempt to promote better storage conditions for this product. Storage facilities are being built with the intention of promoting a rapid removal of this product from the forest and its proper storage until processing.
Among several problems related to storage of agricultural products, the pests of stored grains are responsible for huge losses in rice, corn, soybean, sorghum, and others (Martins et al., 1985;Santos et al., 2002;Caneppele et al., 2003;Silva et al. 2003;Alves et al. 2008;Faroni & Silva, 2008;Alencar et al., 2011). Few species have been reported attacking stored Brazil nut, among them, the larvae of Plodia interpunctella (Lepidoptera: Pyralidae) were observed damaging this product causing galleries damage in almonds (Gomes et al., 2015). Another report was the occurrence of larvae of Curculionidae in chestnuts, damaging the bast and promoting the appearance of grooves in the mesocarp (Castrillón & Purchio, 1988), however, this search does not specify the type(s) of species found, nor refers that the attack occurs in the almond, since the mesocarp of Brazil nut is constituting part of the chestnut and not of the nut. "Broca-do-café" beetle, Hypothenemus hampei (Coleoptera: Scolytidae) was reported attacking the almond of Bertholletia excels (Gumier-Costa, 2009). There is also the report of association of Tribolium confusum and Tribolium ferrugineum in warehouses of Brazil nut, which in this work is referred as Pará nut, but without characterizing or describing the attack and possible damage (Bondar, 1942). It is also reported on the Technical Bulletin of the North Agronomic Institute that T. castaneum attacks Pará nut (Sefer, 1961), however, there are no reports of damage characterization, it is only mentioned that this species may be considered a little harmful to this Amazon product.
The objective of this study was to describe the type of damage caused by adults and immature of T. castaneum in Brazil nuts and verify whether the shell protects the almonds from attack by this pest.

Methods
This work was carried out in the Laboratory of Energy and Pests of Stored Grains (LEPGA) of the Federal University of Mato Grosso, Campus of Sinop, in Sinop, State of Mato Grosso, Brazil. Intact unshelled almonds of the Brazil nut (almonds with fully brown skin) were offered to Tribolium castaneum (adults and immature forms) in order to assess damage. Two experiments were performed. In the experiment 1 -only the adults of this Coleoptera were used, and in the experiment 2, newly hatched larvae.
In the experiment 1, damage caused by T. castaneum adults were assessed in 24-hour periods, for 30 days and 90 days of exposure. Groups of 10 individuals were put in covered plastics pots of 250 ml volume (9.5 cm in diameter and 7.5 cm in height), in a total of 20 repetitions for each evaluation period. In the experiment 2, damage caused by the newly hatched larvae in Brazil nut was evaluated after 24 hours after exposure and in the end of the larval stage evidenced by the emergence of the pupae. Almonds exposed to the adults and immature forms were visually evaluated using a stereoscopic microscope to enable the characterization and description of damage caused by this insect.
Some aspects related to T. castaneum penetration into shelled Brazil nut were also investigated. To perform this bioassay, 60 shelled Brazil nuts were used. From this total, the shells of 30 almonds had been pre-damaged (cracked) using a hammer (Figs. 1 A-D), while the other 30 almonds shells remained intact. Each almond was placed in a plastic pot of 200 ml volume and 10 adults of T. castaneum were introduced. After 30 days, the almonds were removed, opened and checked the occurrence of the pest attack.

Results
Both adult and immature forms of T. castaneum were able to feed on intact Brazil nuts. After 24 hours of exposure of intact unshelled Brazil nuts to the T. castaneum adults, spall was observed, accompanied by fine nut powder on the almond surfaces. The first signs of damage caused by adults are the lesions in the form of scratched surface, it was observed under the stereoscopic microscope (Fig. 2 A  and B). The greatest damage was observed in the nuts exposed to the adults of T. castaneum for 30 days. This damage evolved into galleries on the almond surface (Fig. 2 C and D). Large lesions were observed in the almonds after exposure to T. castaneum for 90 days. These lesions evolved from the galleries to the fully injured portions, which nuts can be distinguishable by changing the original shape ( Fig. 2 E and F). Considering the ability of the T. castaneum to penetrate into the intact shelled Brazil nut and access the interior of the almonds, it was confirmed that the beetles lack this capacity. On the other hand, this pest attacked the almonds with cracked shells (Fig. 3 A  and B). resistance of the Brazil nut surface to penetration by this insect's chewing mouthparts, when compared to the resistance of the surfaces of grains or seeds like corn, rice, soybean and others. Thus, T. castaneum may be classified as a primary pest for Brazil nut.
Damage caused by adults and immature in almonds of Bertholletia excelsa distinguish this insect as a builder of galleries which may evolve into larger lesions. Based on the type of destruction caused by T. castaneum in Brazil nut, this insect may be classified, for this product, as a pest capable of generating quantitative and qualitative damage. In the first one, the attack of T. castaneum caused evident loss of dry matter resulting in losses of bulk, mass, concurring with problems associated with pest attack in other stored grains (Venkatrao et al., 1958;Caneppele et al., 2003). In the second one, the damage may affect seed germination, depreciating the almond and causing nutritional losses, which are the main features of the pest attack in stored products.
The access of the pest to the interior of the Brazil nut is only via cracks in the shell. Besides they were manually made in this study, cracks may occur in the post-harvest and processing steps of this product, especially due to the thermal processes, like drying, for instance. Thus, any type of injury in the shell that allows the insect passage into the interior of the nut will be the only way for the insect to access the almond. However, whether the shell is intact, it prevents the access and attack by the pest due to the resistance and protection that it offers to the almond.
Thus, it may be concluded, from this work, that T. castaneum must be included in the list of pests that attack and have great potential to inflict significant losses in the stored Brazil nut, and may even be considered the primary pest for this product. The damage observed as shallow scrapings, which may develop into galleries and even lesions that modify the original shape of the nut. Finally, the intact shell of Brazil nut ensures the integrity of the almonds, in the event of attack by the beetle T. castaneum.

Discussion
The capacity of the adult and immature forms of Tribolium castaneum to feed on intact unshelled Brazil nut may be explained by the lower degree of resistance of the Brazil nut surface to penetration by