Knowing the trophic links between species is essential to understand their functions in the ecosystem. In this work, we report the first predation record of Rhinella crucifer by the giant water bug Lethocerus grandis. Even though most Brazilian anurans preyed by giant water bugs are smaller than this insect, a larger body size of this predator together with its anesthesic saliva may provide conditions for the subjugation of larger prey.
Conocer los enlaces tróficos entre especies es fundamental para comprender sus funciones en el ecosistema. Aquí, reportamos el primer registro de depredación de Rhinella crucifer por el insecto acuático Lethocerus grandis. Aunque la mayoría de los anuros brasileños depredados por la chinche acuática gigante son más pequeños que este insecto, un tamaño corporal más grande de este depredador junto con su saliva anestésica, puede proporcionar condiciones para la subyugación de presas mayores.
Some characteristics of anuran amphibians vary among Neotropical communities, such as abundance, biomass and body-size. Anurans also go through vulnerable periods in their life cycle, which makes them a fundamental group in trophic webs (Wilbur, 1997; Whiles et al., 2006).
In addition to preying on many types of organisms, anurans also serve as prey to a wide variety of potential predators on land or water, including vertebrates and invertebrates (Toledo, 2005). Among invertebrate predators, the hemipteran family Belostomatidae Leach, 1815 (Hemiptera Linnaeus, 1754) includes species of giant water bugs, a group of carnivorous insects that are distributed widely throughout the world (Ribeiro, 2005). These insects vary in size from medium to large (55 to 85 mm) and act as regulators in aquatic communities through predation (Ribeiro, 2005; Ohba, 2019). Predation by belostomatid insects upon adult bufonids is rare, with two known records for Brazil: one of an adult Rhinella ornata (Spix, 1824) being preyed upon by a Lethocerus grandis Linnaeus, 1758 on the north coast of the state of São Paulo (Haddad & Bastos, 1997), and one of an adult Rhinella mirandariberoi (Gallardo, 1965) preyed upon by a Letocherus annulipes (Herrich Schaeffer, 1845) in the municipality of João Pinheiro, state of Minas Gerais (Valencia-Zuleta et al., 2020).
Seeking to expand knowledge of such interactions, herein we report a new predation record of a Lethocerus grandis preying upon an adult Rhinella crucifer (Wied-Neuwied, 1821). We also provide a list of anuran species predated by giant water bugs of the family Belostomatidae in Brazil. We compiled the list by performing searches of the Google Scholar database (https://scholar.google.com/), using as keywords “Lethocerus grandis AND predat AND Rhinella crucifer” OR “Belostomatidae AND predat AND anuran AND Brazil”. We then checked the references of the recovered manuscripts, looking for additional records of predation events.
The predation event (Fig. 1) reported here was seen at 18:10 h during field work on 23 July 2019, when one of us (CLA) observed an adult Rhinella crucifer with snout-vent length (SVL) of 70 mm, being preyed upon by a Lethocerus grandis (99.2 mm). This interaction took place in a small artificial pond used for fish farming in the municipality of São Francisco do Glória, Minas Gerais, southeastern Brazil (20°48’20” S, 42°19’35” W; 515 m; Datum WGS 84). The site is located in a highly anthropized landscape within the Atlantic Forest biome, with a predominantly pasture matrix. At the observation moment, the air and water temperature were 14ºC and 17ºC, respectively. The toad was alive and struggling at the water surface near the edge of the pond. The giant water bug was positioned on the dorsum of the toad, with the limbs fixed on its ventral region, and the proboscis inserted in its left eye (Fig. 1A). After approximately 20 minutes of observation, both specimens (insect and anuran) were collected. The toad died during transport, and was fixed in formalin 10%, stored in ethanol 70%, and housed at Coleção Herpetológica do Museu de Zoologia João Moojen, of Universidade Federal de Viçosa, Minas Gerais, Brazil (MZUFV 19511). The anuran was identified as R. crucifer by the presence of a fringe on the ventral surface of the tarsus (Baldissera Jr et al., 2004). The giant water bug was identified as L. grandis due to its large body size (total length greater than 85 mm), large anterior tarsal claws as long or longer than the sum of the lengths of both anterior tarsal segments measured externally, and anterior femur slightly longer than the posterior femur (Ribeiro, 2005). There has been no previous record of predation on R. crucifer by a giant water bug, making this the first. Some “reptiles” are the main predators of the genus Rhinella, while records of predation by invertebrates are rare (Oliveira et al., 2017). Our search returned 294 articles, of which 16 were used on this study. Our data show that most of the reported predation events by giant water bugs in Brazil involved small-sized anurans (Appendix 1). It seems likely that the larger size of adult Rhinella may be difficult for these invertebrates to capture and subjugate (Toledo et al., 2007). In the present case, however, the individual Lethocerus grandis was 41.7% larger than its prey. The present observation suggests that the hemipteran large size combined with its anesthetic saliva (Menke, 1979), was sufficient for the hemipteran to subjugate the toad.
Adult male of Rhinella crucifer being preyed on by Lethocerus grandis in southeastern Brazil (A and B).
Fig. 1.— Macho adulto de Rhinella crucifer siendo presa de Lethocerus grandis en el sureste de Brasil (A y B).
Acknowledgements
We thank ICMBio for license permits (#10504–1) and Vertambiental Consultoria, Projetos e Serviços by field support. CLA thanks CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for PhD scholarship. RNF thanks Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq for the productivity fellowship conceded. We thank Eduarda Melo and Erik Wild for the English review.
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Apéndice 1.— Anuros depredados por especies de la familia Belostomatidae en Brasil.
Family/species
Stage
Prey total length (mm)
Predator
Predator total length (mm)
State
Municipality
Reference
Bufonidae
Rhinela crucifer
Adult
69.9
Lethocerus grandis
99.2
MG
São Francisco do Glória
This work
Rhinella mirandaribeiroi
Adult
-
Lethocerus annulipes
-
MG
João Pinheiro
Valencia-Zuleta et al. 2020
Rhinela ornata*
Juvenile
-
Lethocerus grandis
SP
Ubatuba
Haddad & Bastos 1997
Rhinela ornata*
Juvenile
68.2
Lethocerus grandis
95
SP
Ubatuba
Haddad & Bastos 1997
Hylidae
Boana albomarginata
Imago
-
Lethocerus sp.
-
PE
São Lourenço da Mata
Santos 2009
Dendropsophus branneri
Imago
19
Belostoma sp.
-
RN
Macaíba
Baracho et al. 2014
Dendropsophus jimi
Juvenile
21.8
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Dendropsophus minutus
Adult
21.8
Lethocerus delpontei
58.9
ES
São Matheus
Bastos et al. 1994
Dendropsophus minutus
Tadpole
-
Lethocerus sp.
PE
São Lourenço da Mata
Santos 2009
Dendropsophus minutus
Imago
-
Belostoma sp.
PE
São Lourenço da Mata
Santos 2009
Dendropsophus minutus
Juvenile
23.5
Belostoma elongatum
-
SP
Itirapina
Santos 2009
Dendropsophus minutus
Adult
24.3
Lethocerus sp.
31
AM
Manaus
Rocha et al. 2014
Dendropsophus minutus
Tadpole
-
Lethocerus sp.
-
SP
Águas de Santa Bárbara
Serrano et al. 2019
Dendropsophus minutus
Tadpole
-
Lethocerus sp.
-
SP
Águas de Santa Bárbara
Serrano et al. 2019
Dendropsophus minutus
Imago
-
Lethocerus sp.
-
SP
Águas de Santa Bárbara
Serrano et al. 2019
Pseudis platensis
Tadpole
83.3
Belostoma sp.
68
MS
Corumbá
Ceron et al. 2017
Scinax fuscovarius
Adult
-
Lethocerus cf. bruchi
-
SP
Borebi
Maffei et al. 2014
Scinax sp.
Adult
33.4-37
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Scinax sp.
Adult
34.6-36.7
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Scinax sp.
Adult
27.1
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Scinax squalirostris
-
19.5
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Scinax x-signatus
Adult
35
Lethocerus annulipes
66
RJ
São João da Barra
Figueiredo-de-Andrade et al. 2010
Leptodactylidae
Leptodactylus labyrinthicus
Juvenile
-
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Leptodactylus pustulatus
Tadpole
18.9
Belostoma sp.
30
TO
Caseara
Fadel et al. 2019
Physalaemus cf. fuscomaculatus
Adult
40.5
Lethocerus sp.
62.2
MG
Uberlândia
Giaretta & Menin 2004
Physalaemus cuvieri
-
26.1-29.2
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Physalaemus fuscomaculatus
-
41.6
Belostoma elongatum
-
SP
Itirapina
Toledo 2003
Physalaemus nattereri
Adult
40
Lethocerus delpontei
-
GO
Jataí
Batista et al. 2013
Physalaemus nattereri
Adult
-
Lethocerus annulipes
-
PR
Diamante do Norte
Batista et al. 2013
Physalaemus nattereri
Adult
-
Lethocerus annulipes
-
MG
João Pinheiro
Valencia-Zuleta et al. 2020
Physalaemus nattereri
Adult
-
Lethocerus annulipes
-
MG
João Pinheiro
Valencia-Zuleta et al. 2020
Physalaemus nattereri
Adult
-
Lethocerus annulipes
-
MG
João Pinheiro
Valencia-Zuleta et al. 2020
Physalaemus nattereri
Adult
-
Lethocerus annulipes
-
MG
João Pinheiro
Valencia-Zuleta et al. 2020
Microhylidae
Chiasmocleis albopunctata
Adult
-
Not identified
-
MG
Santana do Riacho
Yves et al. 2018
States abbreviations: PE – Pernambuco; RN – Rio Grande do Norte; ES – Espirito Santo; SP – São Paulo; AM – Amazonas; MS – Mato Grosso do Sul; RJ – Rio de Janeiro; GO – Goiás; PR – Paraná; MG – Minas Gerais and TO – Tocantins. * Treated as Bufo crucifer by Haddad & Bastos (1997).