Host-seeking behavior of the Heterorhabditis amazonensis nematode in response to stimulant sources1

Vanessa Andaló,Alcides Moino Junior,Grazielle Furtado Moreira

doi:10.1590/1983-40632016v4745395

Abstract

ABSTRACT Several species of entomopathogenic nematodes have different host-seeking methods, and could be considered as "ambusher" or "cruiser". These differences may depend on how the nematodes detect the volatile signals used as cues for foraging. This study aimed to evaluate the locomotor response of Heterorhabditis amazonensis RSC5 to the compounds from root exudates of different plants, as well as to stimulants produced by the presence of insects or to the feeding activity of insects on plants. Arenas with agar-water substrates, containing root exudates from corn, bean, soybean, cucumber, garlic and tomato seedlings, were assembled to determine the substrates possibly preferred by H. amazonensis.Arenas with sand were also constructed to include, besides the seedling root exudates, treatments containing Spodoptera frugiperda, garlic seedlings and S. frugiperda feeding on garlic seedlings. The H. amazonensis species was attracted to the volatile chemicals emitted by all the root exudates tested, especially the exudate from garlic seedlings. However, it showed the greatest attraction to the combination of garlic seedlings and S. frugiperda, indicating that the search of H. amazonensis for its host is enhanced by the association between the insect and the volatile chemical compounds produced by plants, when attacked by insects.

Highlights

Plants and insects have coexisted for approximately 350 million years and have developed elaborate systems that highlight the tritrophic interplay among plants, insect herbivores and their natural enemies
When the displacement of the H. amazonensis infective juveniles was measured using the onechoice test in Petri dishes containing water-agar, they were attracted to all the root exudates
The garlic plant root exudates attracted the largest number of infective juveniles, followed by the tomato seedling root exudates, cucumber and soybean root exudates, and, the root exudates from the corn and bean seedlings

Summary

Introduction

Plants and insects have coexisted for approximately 350 million years and have developed elaborate systems that highlight the tritrophic interplay among plants, insect herbivores and their natural enemies. Just as plants can attract predators and parasitoids, including natural enemies, they can interact with pathogens (Elliot et al 2000). The ability to attract natural enemies is referred to as a type of induced resistance (defense), in which the attacked plant produces and releases volatile chemicals that serve as signals to attract natural enemies (Walton 1997). Roots are likely the most suitable region of the plant for entomopathogens of soil pests to attack, because the soil is rich in microorganisms that can suppress the population of insects that feed on roots in natural ecosystems (Rasmann et al 2005).

Objectives

Methods

Results