Coconut trees of the cv. Green Dwarf of Jiqui in Bahia, northeastern Brazil, that displayed hartrot symptoms were cut and inspected for the presence of insect vectors in the leaf axils. Eggs, nymphs and adults of Lincus lobuliger Breddin (Hemiptera: Pentatomidae), vector of the protozoan causing hartrot, were collected together with an abundance of adults of the predatory beetle Hololepta (Leionata) quadridentada (Olivier) (Coleoptera: Histeridae). In the field, both were placed in a plastic container for transport, and the predation of L. lobuliger eggs by the histerid was observed. The predation was subsequently confirmed under controlled laboratory conditions. Here, we report for the first time H. quadridentada preying on L. lobuliger eggs, suggesting that the histerid contributes to the natural biological control of this vector. Moreover, our results could contribute to the development of biologically sound control strategies against L. lobuliger or other Lincus species.
In Brazil, hartrot of coconut was first described in the state of Bahia in 1982 (Bezerra & Figueiredo 1982). In 1987, yield losses from 26.5 to 34% caused by this disease were recorded in coconut plantations in the state of Pernambuco (Mariano et al. 1990). Outbreaks of hartrot also have been reported in the states of Alagoas, Sergipe, Paraíba and Mato Grosso (Souza 2005). The disease usually attacks productive coconut trees, and depending on the vector population, dissemination is rapid, resulting in an almost complete elimination of the plantation. The pathogenic microorganism Phytomonas staheli McGhee & McGhee (Protozoa: Trypanosomatidae) is associated with hartrot of coconut (Parthasarathy et al. 1976).
Lincus lobuliger Breddin (Hemiptera: Pentatomidae: Discocephalinae), which occurs only in northeastern Brazil, is one of the most threatening pests of palm trees because it is capable of transmitting trypanosomatids of the genus Phytomonas (Fig. 1) (Rolston 1983; Resende et al. 1986; Panizzi et al. 2000; Sgrillo et al. 2005; Campos & Grazia 2006). The stink bug L. lobuliger, one of 35 members of the genus, is a black pentatomid approximately 9.4 to 12.0 mm in length. The adults dwell in the petiole axils of coconut leaves, where they feed on the sap (Moura & Rezende 1995; Panizzi et al. 2000).
Overall, species of Lincus are photophobic, and hide in well-sheltered areas at the base of the leaf rachis. Their dispersal probably occurs by nocturnal flights and by walking and climbing along the trunk (Couturier & Kahn 1989; Llosa et al. 1990; Dollet 2016). In a coconut plantation, a visual inspection of the fronds or stems is not adequate to locate Lincus spp. It is only by gently pulling down the rachis of a lower frond that these insects are found hiding in a very humid environment with large amounts of plant debris, notably the remnants of male flower bracts (Dollet 2016).
Thus, in an attempt to rear L. lobuliger in the laboratory for biological and control studies, insects were collected from cv ‘Green Dwarf’ of Jiqui coconut trees, in a rural area of Valença (13.2850°S, 39.2550°W to 13.2950°S, 39.2650°W) in southern Bahia. In short, coconut trees showing hartrot symptoms were identified and cut at the stem base. Thereafter, the leaves were removed and the axils and organic matter contained in the leaf sheaths were examined for insects.
During a first visit to collect Lincus spp. in Nov 2015, several specimens were found. In contrast, in a subsequent visit in Jul 2016, fewer stink bugs were found. It is noteworthy that during later sampling there was the frequent presence of adults of a clown beetle, which were collected and identified as the predator Hololepta (Leionata) quadridentada (Olivier) (Coleoptera: Histeridae). The collected beetles were placed in the same container as the eggs, nymphs, and adults of the stink bug. At the end of the day, Lincus eggs were observed on the mouthparts of the histerid beetles.
To confirm the observed predation behavior in the laboratory, the 4 beetles were placed in a Petri dish (60 × 15 mm) with 2 stink bug egg clusters (with 8 and 10 eggs each), and H. quadridentada feeding on L. lobuliger eggs was recorded. A further visit was conducted in Nov 2016, and a very small number of L. lobuliger was observed, but the presence of H. quadridentada on almost all of the 11 felled coconut trees was noted.
Hololepta quadridentada has been reported on avian farms as a natural enemy of arthropods that develop on poultry litter (Gianizella & Prado 1998; Lopes et al. 2006). In agricultural settings, this beetle has been reported as a natural predator of Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) and Scyphophorus acupunctatus Gyllenhal (Coleoptera: Curculionidae), which are pests of banana and agave cactus, respectively (Mesquita 2003; Velázquez et al. 2006).
In spite of the broad geographic distribution of the species (South and Central America) (Mazur 2011), and having been reported as economically relevant, the recognition of the taxon is currently difficult. Hololepta quadridentada can be distinguished from other Neotropical species of the genus by a more convex-shaped body, without frontal striae; the pronotum is regularly curved on the sides, without coarse punctures, and with lateral striae along all lateral edges; the elytra with the first dorsal stria abbreviated and the second dorsal stria complete; the inferior carina of the medium and posterior tibiae possess teeth; the pygidium possesses deep and dense punctuation. Also, males have a deep hole on the anterior angles of the pronotum (Fig. 2).
Due to the transmission of hartrot, the damage inflicted by L. lobuliger on coconut palms in northeastern Brazil is severe. Regarding the biological control of L. lobuliger, little is known about its natural enemies. An egg parasitoid complex was mentioned by Moura & Resende (1995), but no data are available on its impact on L. lobuliger populations. The presence of a protozoan morphologically similar to P. staheli in the digestive tract of Arilus sp. (Heteroptera: Reduviidae) captured in the field was observed by Meneguetti & Trevisan (2010), who suggested that it might be possible to control Lincus sp. biologically by the introduction of these reduviid predators.
Here, we report for the first time H. quadridentada preying on eggs of L. lobuliger, suggesting that this histerid contributes to the natural biological control of this vector. In addition, our results may contribute to the development of biologically sound control strategies against L. lobuliger or other Lincus species. Further research should focus on the efficiency of H. quadridentada as predator of Lincus spp. eggs, as well as on the natural enemy complex associated with this pest.
The authors are grateful to Luiz Alexandre Campos for the identification of L. lobuliger and Henri Pierre Aberlenc for the photos of Lincus.