Hypsipyla grandella (Lepidoptera: Pyralidae) is found throughout Central and South America, except in Chile. Damage caused by this pest in native trees of the subfamily Swietenoideae (Meliaceae) is so intense and severe that it makes industrial forestry with those species unfeasible. It also may damage fruits and seeds of those trees. Damage to reproductive structures may compromise natural regeneration and impair seedling production. Management tactics for this pest include the use of resistant exotic Meliaceae, such as the Australian red cedar (Toona ciliata M. Roem.) and the African mahogany (Khaya ivorensis). The objective of this work was to report, for the first time, damage to K. ivorensis fruits and seeds by H. grandella in Brazil. The study was carried out in a plantation for sawwood production, with about 73,000 trees of K. ivorensis in 175 ha in Corinto, Minas Gerais, Brazil. Ripe and almost ripe bored fruits were collected from the soil beneath 8-yr-old trees in May 2018. The total number of fruits and seeds damaged, the numbers of larvae, pupae, and adults of H. grandella per fruit, the presence of other species, and behavior of this pest were observed. Ten fruits bored by H. grandella were collected. The fruits were damaged internally by larvae of this pest, and half of them had exit holes. Each fruit had, on average, 33.6 seeds, with 99.4% of the seeds damaged, plus 4.2 H. grandella at different development stages. Some fruits did not have the borer, but they were damaged and had the characteristic exit holes of this species. The average number of larvae per fruit was 3.4, with up to 13 larvae in a single fruit. The damage in African mahogany shoots reported in 2016, and the current damage on fruits and seeds show that resistance of K. ivorensis to H. grandella has been broken, probably due to selective pressure over the large area planted with this tree in Brazil. African mahogany plantation viability in Brazil will be affected.
The genus Hypsipyla (Lepidoptera: Pyralidae) is found throughout the tropics, and its larvae, which are specialized borers of trees in the family Meliaceae, may damage twigs, branches, leaves, bark, flowers, fruits, and seeds (Taveras et al. 2004; Cunningham et al. 2005; Castro et al. 2016). The mahogany shoot borer, Hypsipyla grandella Zeller, is found throughout Central and South America, except in Chile (Perez et al. 2010a). Damage caused by this pest on trees of the subfamily Swietenoideae (Meliaceae), such as mahogany (Swietenia macrophylla G. King) and cedar (Cedrela spp.), is so intense and severe that they can make commercial plantations of these species unfeasible (Pérez-Salicrup & Esquivel 2008; Jesus-Barros et al. 2015; Castro et al. 2016).
The principal damage occurs when H. grandella larvae feed on meristematic shoot tissues, causing loss of apical dominance, bifurcations, and deformations, and resulting in reduction in the economic value of the trees (Zaché et al. 2013; Barradas-Juanz et al. 2016a). There are no effective techniques to control this pest, and integrated management has failed to reduce damage to acceptable levels (Barradas-Juanz et al. 2016b; Castro et al. 2017). The principal strategies to reduce damage by H. grandella larvae, with different success rates, are biological and chemical control, and plant resistance (Perez et al. 2010b; Ruiz et al. 2016; Castro et al. 2017).
Exotic Meliaceae, from similar edaphoclimatic regions to those of Brazil (Alves-Júnior et al. 2017) are less susceptible to H. grandella than native species (Cunningham et al. 2005; Perez et al. 2010a). African mahogany (Khaya ivorensis A. Chev.) (Meliaceae) plantations began in the mid-1970s in the northern region of Brazil and spread during the late 80s, with seedlings originating from seeds (Ribeiro et al. 2016). Restrictions in the market of native Meliaceae (usually endangered species), the high wood quality, and the high resistance of K. ivorensis to H. grandella encouraged expansion of mahogany plantations using this tree in Brazil (Alves-Júnior et al. 2017; Ribeiro et al. 2017, 2018). However, H. grandella has started damaging K. ivorensis shoots in Brazil (Zanetti et al. 2017).
The mahogany shoot borer damages native Meliaceae fruits and seeds in Brazil (Pinto et al. 2013; Castro et al. 2017). These reproductive structures are a good source of protein and minerals for insect nutrition (Pinto et al. 2013), and are used to culture H. grandella in the laboratory (Barradas-Juanz et al. 2016a; Castro et al. 2016). Damage to reproductive structures may compromise natural forest regeneration (Jesus-Barros et al. 2015), and reduce available material for seedling production (Pinto et al. 2013)
The objective of this study was to report, for the first time, damage on K. ivorensis fruits and seeds by H. grandella in Brazil. The study was carried out in a K. ivorensis plantation for sawn wood production, with about 73,000 trees in 175 ha, spaced 5 × 5 m, in the municipality of Corinto, Minas Gerais, Brazil (18.427500°S, 44.431389°W, 672 masl). Planting was done from Nov 2009 to Nov 2011. Seven-yr-old eucalyptus plantation, pasture, and regenerated “Cerrado” (Brazilian savannah) areas surrounded the K. ivorensis plantation. The predominant vegetation in the region is Cerrado, with tropical climate, dry season (Köppen-Geiger climatic classification: Aw), average annual precipitation and temperature of 1,157 mm and 22.4 °C, respectively. Clay-rich yellow latosol predominates, and the topography varies from flat to smooth wavy.
Ripe or almost ripe bored fruits were collected in May 2018 from the soil beneath K. ivorensis trees in an 8-yr-old stand. These fruits were taken to the Laboratory of Applied Forest Entomology of the Federal University of Minas Gerais in Montes Claros, Minas Gerais, Brazil, where each fruit was analyzed. The total number of damaged fruits and seeds, total number of H. grandella larvae, pupae, and adults per fruit, presence of other organisms, and behavioral aspects of this pest were observed. The identification of H. grandella was based on external morphological characteristics of all stages of this insect.
Ten K. ivorensis fruits bored by H. grandella were collected (Fig. 1-A). These fruits were internally damaged by larvae of this pest (Fig. 1-B), and half of them had exit holes (Fig. 1-A). Each fruit had, on average, 33.6 seeds, with 99.4% of the seeds damaged (Fig. 1-C), and 4.2 H. grandella individuals at different development stages. Some fruits did not contain the insect, but they had characteristic H. grandella injuries and external exit holes. The mean number of larvae per fruit was 3.4, with up to 13 larvae in a single fruit (Fig. 1-D). Two fruits had 1 and 4 pupae (Fig. 1-E), respectively, and another fruit had 3 H. grandella adults (Fig. 1-F). Other insects were found in half of the fruits evaluated, including Diptera larvae in 3 fruits, and 3 Dermaptera adults in 1 fruit.
This is the first record of H. grandella damaging K. ivorensis fruits and seeds, an exotic plant in Brazil. This is important because this plant was introduced due to the damage caused by this insect in native Meliaceae, such as Carapa guianensis Aubl., Carapa procera DC., Cedrela fissilis Vell., and S. macrophylla (Pinto et al. 2013; Castro et al. 2018). The report of damage by this pest in African mahogany shoots in 2016 (Zanetti et al. 2017), and this report on fruits and seeds, show that the resistance of K. ivorensis to H. grandella was broken by selective pressure acting over the large area cultivated with this plant in Brazil (Zanetti et al. 2017). In addition, a major concern is the fact that approximately 200 km separates the region where the damage was reported in shoots of K. ivorensis with damage to fruits and seeds, suggesting that this problem might be occurring in an extensive area of Brazil.
The total of 13 larvae in a single K. ivorensis fruit is higher than that reported for this species occurring in C. fissilis, where only 1 larva occurred on average, with a maximum of up to 4 per fruit (Castro et al. 2018). This may be due to the cannibalism of smaller larvae by larger and older ones in C. fissilis fruits with many larvae. In addition, the survival of a larger number of larvae per K. ivorensis fruit may indicate a better quality of this host for the larvae of this pest. Up to 4 pupae of H. grandella were found in a single fruit of K. ivorensis, but only 1 pupa was reported in C. fissilis fruits (Castro et al. 2018).
The K. ivorensis seeds were mostly damaged by H. grandella, with greater damage than that reported for Carapa spp. injured by Hypsipyla ferrealis Hampson (Lepidoptera: Pyralidae) and H. grandella, and of C. fissilis by H. grandella (Pinto et al. 2013; Castro et al. 2018). A diet based on S. macrophylla seeds may contain the essential nutrients for development of this insect (Castro et al. 2016). Adults of H. grandella from larvae feeding on seeds of K. ivorensis developed regularly, but H. grandella larvae, when reared on leaves of Khaya senegalensis (Desv.) A. Juss. (Meliaceae), have produced malformed adults (Perez et al. 2010a). Seeds of K. ivorensis may contain the essential elements for the development of this pest, and those damaged may lose germination potential (Pinto et al. 2013). Even seeds that are partially eaten may have their germination capabilities affected, and production of seedlings in nurseries may suffer, or generate less vigorous seedlings that are more susceptible to the attack by this pest in the field.
The viability of K. ivorensis plantations in Brazil should be reevaluated due to recent evidence of the resistance breakdown of this species by H. grandella. Damage to fruits and seeds impairs seedling production of K. ivorensis and may be a source of inoculum for healthy trees.
We thank the Brazilian institutions “Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq),” “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Superior (CAPES/PELD),” “Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG),” and “Programa Cooperativo sobre Proteção Florestal/PROTEF” of the “Instituto de Pesquisas e Estudos Florestais/IPEF” for financial support, and “União Empreendimentos Rurais Ltda.” for general assistance during this project.