Trap rebuilding by Myrmeleon brasiliensis larvae (Neuroptera: Myrmeleontidae) in response to flooding: the effect of body size / Reconstrucción de trampas por larvas de Myrmeleon brasiliensis (Neuroptera: Myrmeleontidae) tras las inundaciones: efecto del tamaño corporal

Abstract Introduction: Immature forms of the antlion Myrmeleon brasiliensis (Neuroptera, Myrmeleontidae) build traps in dry sandy soil to capture prey. Objective: The aim of the present study was to investigate how the waterlogging of the soil due to rain affects the trap rebuilding and relocation behavior of M. brasiliensis of different sizes. Methods: The study was conducted between July and December 2019. Larvae M. brasiliensis were observed and collected from a forest reserve in the municipality of Aquidauana in the state of Mato Grosso do Sul, Brazil. Results: In the natural environment, most larvae rebuilt their traps in the same location seven days after the simulation of rain, with a smaller diameter than that observed prior to the simulation of rain. In the laboratory, the movements of M. brasiliensis larvae and rebuilding of the traps after the waterlogging of the soil was affected by body size. Larger larvae moved more and were more likely to rebuild their traps. Conclusions: The saturation of the soil affects the foraging of M. brasiliensis larvae, which are impeded from rebuilding their traps for a period. In situations of long periods of saturated soil, the mortality rate of the larvae is high and rebuilding of the traps occurs after the soil dries out, but with a smaller trap size. These data suggest that changes in the rainfall pattern can affect the population structure of M. brasiliensis larvae, with the selection of larger individuals in situations of more severe rains. In this process, the smaller larvae are more affected, as their foraging is impeded.

Resumen Introducción: Los insectos inmaduros de hormiga león de la especie Myrmeleon brasiliensis (Neuroptera, Myrmeleontidae), construyen trampas en el suelo arenoso seco para capturar a sus presas. Objetivo: El objetivo de este trabajo fue analizar cómo la inundación del suelo, como la lluvia, afecta al comportamiento de reconstrucción y de desplazamiento de las trampas de M. brasiliensis según las diferentes tallas. Métodos: El estudio fue conducido entre julio y diciembre del 2019. Las larvas fueron observadas y recolectadas en una Reserva Forestal en la ciudad de Aquidauana, Estado de Mato Grosso del Sur, Brasil. Resultados: Observamos que, en el ambiente natural, siete días después de la lluvia simulada, la mayoría de las larvas reconstruyeron a sus trampas en el mismo sitio y con diámetro más pequeño que el observado antes de la lluvia simulada. En el laboratorio fue observado que después de la inundación del suelo, el desplazamiento de las larvas y la reconstrucción de las trampas es afectado por el tamaño de su cuerpo. Así, larvas de M. brasiliensis más grandes se desplazan más y presentan una probabilidad más grande de reconstruir a sus trampas. Conclusión: De esa manera, la inundación del suelo afecta el forrajeo de las larvas M. brasiliensis, que se quedan impedidas por un tiempo durante la reconstrucción de sus trampas. Además, en situaciones de largos periodos de inundación del suelo, las larvas presentan una alta tasa de mortalidad y la reconstrucción de sus trampas ocurre después que se seca el suelo, pero esas trampas suelen ser más pequeñas. Esos datos sugieren que es posible que variaciones en el patrón de lluvia pueden afectar la estructura poblacional de las larvas M. brasiliensis, pues en situaciones de lluvias más fuertes, las larvas más grandes suelen tener más éxito. En este proceso, las larvas más pequeñas se ven más afectadas, ya que se impide su búsqueda de alimento.

Effect of asymmetric competition on distance among Myrmeleon brasiliensis (Návas, 1914) (Neuroptera: Myrmeleontidae) larvae

In cases of asymmetric competition, larger individuals of many animal species have a greater probability of acquiring territory, gaining initial access to resources and finding a mate in comparison to smaller individuals. The competition among larvae of the antlion Myrmeleon brasiliensis (Neuroptera, Myrmeleontidae) is observed in the search for space for the construction of traps, in the forage for prey, and in the occurrence of cannibalism. The body size of the larvae is proportional to the size of the traps and the success of predation. Thus, larger specimens are better competitors in terms of capturing preys (asymmetric competition). The aim of the present study was to determine the effects of asymmetric competition in M. brasiliensis regarding the distance among these larvae. The study was developed in a permanent reserve area, located in the municipality of Aquidauana, from the Mato Grosso do Sul state, Brazil. For the laboratory experiments, we collected M. brasiliensis larvae and placed two larvae in plastic pots. The observations occurred by the visual search of traps, when a larva was seen in the diameter of its trap and the trap of its closest neighbor. Next, the trap size and the distance between them were measured for a period of 15 days. The results of the present study demonstrate that the largest M. brasiliensis larvae were outside the clusters. Within these clusters, the larvae moved away from each other because of the size of their traps, as the larger the neighboring larvae the greater the distance between them. Thus, the asymmetric competition between M. brasiliensis (larger larvae are better competitors) suggests a spatial arrangement among the larvae that is guided by the variable size of the trap.

Cannibalism among Myrmeleon brasiliensis larvae (Návas, 1914) (Neuroptera, Myrmeleontidae) / Canibalismo entre as larvas Myrmeleon brasiliensis (Návas, 1914) (Neuroptera, Myrmeleontidae)

Cannibalism is influenced by various intrinsic and extrinsic factors of the population, such as density, population structure, prey availability, habitat structure and famine. These factors acting either independently or in synergy determine the frequency of cannibalism. The aims of the present study were to evaluate the effect of density and food availability on the occurrence of cannibalism among Myrmeleon brasiliensis larvae (Neuroptera, Myrmeleontidae). In the present study, the occurrence of cannibalism among M. brasiliensis larvae was greater in the treatments that simulated an absence of food in situations of both high and low density. The search for food makes a larva move about to forage, thereby increasing the risk of falling into the trap of a neighboring larva. Thus, the cannibalistic behavior of M. brasiliensis larvae may be associated with opportunity rather than a direct attempt to pray on the same species.

O canibalismo pode ser influenciado por vários fatores intrínsecos e extrínsecos à população, tais como a densidade, a estrutura da população, a disponibilidade de presas, a estrutura do habitat e o nível de fome. Todos esses fatores podem atuar independentemente ou de forma sinérgica para determinar a frequência de canibalismo. Os objetivos deste estudo foram avaliar o efeito dos fatores densidade e da oferta de alimento na ocorrência de canibalismo entre as larvas Myrmeleon brasiliensis (Neuroptera, Myrmeleontidae). Foi observado que tanto em situações de baixa densidade quanto de alta densidade o canibalismo é maior nos tratamentos que simularam a falta de alimento. A busca pelo alimento faz com que as larvas se desloquem; esse deslocamento contribui para que uma larva M. brasiliensis caia na armadilha da larva vizinha. Dessa maneira, o comportamento canibal entre M. brasiliensis pode estar associado à oportunidade, e não a uma busca direta pela presa da mesma espécie.