Project Number: 8010-22000-032-000-D
Project Type: In-House Appropriated
Start Date: Jul 2, 2020
End Date: Jul 1, 2025
Objective 1: Determine the genetic basis of the host ranges and climatic tolerances of pest herbivorous insects and parasitoids of these pests with a focus on using molecular genetic methods to elucidate factors responsible for the evolution of host specificity, to predict responses to climate change, and to develop methods for management of pest impacts. [NP304, C1, PS1A; C3, PS3A, 3B and 3C] Sub-objective 1.A – Determine genetic basis of differences in host specificity of aphid parasitoids. Sub-objective 1.B – Measure genetic variation in responses of parasitoids and their aphid hosts to different temperature regimes. Sub-objective 1.C – Develop and test mathematical models for impact of climate change on population dynamics and evolution of parasitoids and aphid hosts. Objective 2: Determine interactions between biological control, plant resistance, and aphid virulence in their effects on virulence frequencies. [NP304, C1, PS1A; C3, PS3A and 3B] Sub-objective 2.A – Measure interactions between resistance, virulence, and parasitoids in their effects on virulence frequencies. Sub-objective 2.B – Develop and test mathematical models of interactions between plants, aphids, and parasitoids in their effects on virulence frequencies. Objective 3: Determine molecular phylogenetic relationships, test host specificity, and introduce parasitoids for biological control of target aphids. [NP304, C1, PS1A; C3, PS3A and 3B] Sub-objective 3.A – Determine molecular phylogenetic relationships of parasitoids. Sub-objective 3.B – Test host specificity of parasitoids of pest aphids. Sub-objective 3.C – Introduce parasitoids against pest aphids. Sub-objective 3.D – Measure the impact of the introduced parasitoids on distribution and abundance target and non-target aphid species.
Hypotheses about genetic architecture of host specificity have two extremes: (a) few genes with large effects that interact additively; (b) many genes of small effects that interact epistatically. We will take two approaches to testing these hypotheses. In one approach, we will use hybridization of A. atriplicis and A. certus in the laboratory to map QTL affecting parasitism of D. noxia, a host for A. atriplicis and a non-host for A. certus. We will cross A. atriplicis into A. certus with multi-parent advanced generation intercrosses and inbreed the intercrosses to make recombinant inbred lines (RILs). We will genotype SNPs in the RILs, make a linkage map, measure parasitism of D. noxia by these lines, and map QTL affecting parasitism. In the other approach, we will map QTL involved in differences between lines of A. rhamni reared for >140 generations on R. padi versus control lines reared on A. glycines. We will cross and backcross these lines, make a linkage map based on SNPs, measure parasitism of R. padi by backcross females, and map QTL affecting parasitism. We will test whether genes that diverge in sequence and/or expression between RIL and backcross females are associated with QTL found above. We will do this by genotyping RIL and backcross females for alleles in divergent genes and integrating these genes onto the QTL maps. To find genes that diverge in sequence or expression between A. atriplicis and A. certus and between selection and control A. rhamni, we have sequenced and assembled their genomes and transcriptomes. We will test whether divergent genes associated with QTL are expressed in sensilla on antennae, ovipositor, or mouth partsby hybridizing probes for the genes in parasitoids and imaging whole-mounts microscopically. We will whether divergence in gene sequences or expression levels correlate with differences in host specificity, host acceptance, and host suitability among Aphelinus species. We will measure genetic variation in temperature responses of parasitoids and their hosts that could allow adaptation to new temperature regimes using isofemale lines. We will develop and test mathematical models for the impact of climate change on population dynamics and evolution of parasitoids and hosts. To test this whether parasitoids slow the increase in frequency of virulent aphid genotypes that can overcome host plant resistance, we will do within-generation to get parameter estimates and multi-generation experiments to test the effects of parasitoids on viruluence freqencies. We will also develop and test mathematical models of interactions between plants, aphids, and parasitoids in their effects on virulence frequencies. We will continue to determine molecular phylogenetic relationships of parasitoids in the genus Aphelinus. We will continue to test the host specificity of parasitoids of pest aphids, and we will introduce parasitoids with narrow host range and measure their impact on the distribution and abundance target and non-target aphid species.