A simple in vitro method to study interactions between soil insects, entomopathogenic fungi, and plant extracts

Abstract

A combined application of a biological control agent, such as an entomopathogenic fungus (EPF), with other means of pest control may lead to enhanced or more reliable efficacy of the biocontrol agent. Ideally, the combined components would interact synergistically, yielding significantly higher mortality of the target pest. The mode of such interactions is often unclear and particularly difficult to elucidate for soil-dwelling pests. Here, an efficient image analysis protocol was developed to study behavioural responses of soil-dwelling insects to application of control measures in two-dimensional terraria. The interactions between the EPF Metarhizium brunneum Petch (Hypocreales), a supposedly repellent extract of garlic, Allium sativum L. (Amaryllidaceae), and wireworms, Agriotes obscurus (L.) (Coleoptera: Elateridae), as target hosts were investigated. Tunnelling activity and mortality of wireworms were studied under choice and no-choice situations of various combinations of the control agents. A treatment with Metarhizium spores resulted in wireworm mortalities of about 80%. Contrary to expectations, a combination of the EPF with the garlic extract did not increase, but slightly decrease wireworm mortality. The data gained from the image analysis revealed that the tunnelling activity of wireworms was clearly reduced in the presence of garlic, which, together with a reduced germination rate of spores, is a possible explanation for the antagonism detected in the combined treatment. The methodological approach developed here can be used to study the interactions among control agents and soil insects over several days and weeks.

Assessing effects of the entomopathogenic fungus Metarhizium brunneum on soil microbial communities in Agriotes spp. biological pest control

“…In the pot trial of this study, the combined treatments of M. brunneum ART2825 and garlic capsules (FCBK + G cap , F cap + G cap ) did not enhance efficacy, an observation which was also made in a laboratory experiment using two-dimensional terraria (Eckard et al. 2017 ). One reason for insufficient control of Agriotes larvae may be a repelling effect of Metarhizium spp.…”

“…Among those, garlic was shown to repel and reduce movement of A. obscurus larvae, which potentially may enhance the efficacy of M. brunneum by weakening the larvae and making them more susceptible to a fungal infection (Eckard et al. 2017 ).…”

Development of an attract‐and‐kill co‐formulation containing Saccharomyces cerevisiae and neem extract attractive towards wireworms

“…Moreover, co‐application of neem extract and EPFs like Metarhizium spp. is an interesting approach, because synergistic actions between neem and different EPFs are known for other insect pests, and simple methods for studying interactions between soil insects, EPFs and plant extracts have been developed recently . However, it should be noted that costs for the attract‐and‐kill approach using the formulation presented here are expected to be higher than for synthetic insecticidal compounds currently used for wireworm control.…”

Synergic effects of some plant-derived essential oils and Iranian isolates of entomopathogenic fungus Metarhizium anisopliae Sorokin to control Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae)

“…It has been highly recommended that EPF are applied in combination with other control means, such as plant-derived essential oils (EOs), which increases insect control efficiency (Borgio et al, 2008;Mohamed, 2009;Kovendan et al, 2012;Murugan et al, 2014;Batta and Kavallieratos, 2018). However, some incompatible relationships have been found between EPF and EOs, which restrict the simultaneous application of these control tools (Akbar et al, 2005;Mohamed, 2009;Eckard et al, 2017). Therefore, EPF-EOs interactions needed to be investigated before their application against insect pests.…”