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    Research

    Enhancing Biological Pest Control: Learning Mechanisms and Olfactory Conditioning in Parasitoid Wasps

    Abstract

    Damage associated with invertebrate pests has been shown to reduce the yield of major crops worldwide (wheat, maize, rice, potato and soybean) by up to 23% on average, threatening food security and causing substantial economic losses, thus, crop protection is pivotal. In India, the second largest producer of vegetables globally, insect pests account for 36% of yield losses. Crop pests have predominantly been managed by the use of synthetic chemical pesticides but their negative impacts on the environment and human health have put greater focus on the development of more environmentally sustainable strategies. Augmentative biological control is a progressive sustainable method that involves the release of commercially reared natural enemies in enclosed agroecosystems to supress the population of a target pest below its economic threshold (Collier and Steenwyk, 2004). Parasitoid wasps are notable biocontrol agents that are extensively used in inundative and inoculative biocontrol schemes. However, they can be slow to establish upon release because they are mass-reared under traditional systems that do not accommodate the cognitive processes underlying how they locate, recognise and memorise their hosts. Host-searching behaviour is vital for female parasitoid fitness and reproduction. This behaviour primarily relies on chemical cues mediated from their environment and follows a three-level process: (1) host habitat location using herbivore-induced plant volatiles (HIPVs), (2) host location using HIPVs and other host-originating chemical cues and (3) host discrimination and acceptance using cues directly derived from the host. Parasitoid behavioural responses to chemical cues can be either innate or learned. Learning in response to chemical cues can occur in different parasitoid life-cycle stages. For instance, experiences during the larval stages can influence the adult responses to chemosensory cues (Hopkinā€™s host selection principle). Adult stage learning usually takes the form of an association between a particular odour and a successful oviposition experience. Despite the vast majority of laboratory-based studies evidencing parasitoid learning, the extent to which parasitoids are capable of learning is poorly understood and the importance of it in determining their efficacy as biocontrol agents under semi-field conditions has not been demonstrated (Kruidhof et al., 2019). An improved understanding of parasitoid learning capacities could be utilised to implement olfactory conditioning during their commercial mass rearing. This would see the behavioural manipulation of parasitoid responses in order to improve the speed with which biological controls respond to specific chemical cues associated with a target crop pest and thus improve their efficiency as biocontrol agents.

    Description

    Project Aim: This project will characterise parasitoid learning in relation to chemical cues associated with host-searching and explore how insect learning can be used to improve the efficiency of parasitoids as biological control agents in a sustainable crop protection. Specific objectives include:

    O1. Characterise chemical cues associated with host-searching behaviour. Chemical cues such as, HIPV’s and host-derived cues will be identified through insect behavioural studies (e.g., olfactometer bioassays) combined with analytical chemistry approaches (e.g., GC-MS analyses).

    O2. Determine the learning abilities of commercially available parasitoids in response to aphid-infested plants. Different learning mechanisms such as, associative learning, sensitisation and priming will be implemented in an array of behavioural experiments and their impact to different parasitoid developmental stages (e.g., larva, adult) will be examined.

    O3. Develop mass-rearing techniques that manipulate parasitoid learning to enhance host-searching for specific aphid pests and crops. Results from O1 and O2 will be evaluated and utilised for the development of an optimal olfactory conditioning technique which will be technically implemented in the laboratory mass-rearing systems. Conditioned parasitoids will be examined through different behavioural studies (e.g., olfactometer and wind tunnel bioassays).

    O4. Evaluate the impact of improved parasitoid learning on biological control efficacy under semi-field (glasshouse) conditions. Laboratory olfactory conditioned parasitoids will be evaluated though behavioural studies under bigger scale glasshouse conditions.

    O5. Assess whether biotic factors such as plant disease infection impact parasitoid host-searching efficacy. Volatile organic compounds (VOC’s) derived from diseased plants will be examined in response to parasitoid learning behavioural studies (e.g., olfactometer bioassays).

    Funding Body

    Harper Adams University

    Lead Organisation

    Harper Adams University

    Partners

    Biobest

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