DOI: 10.5061/dryad.gmsbcc2s1
title: Data for: A diverse parasite pool can improve effectiveness of biological control constrained by genotype-by-genotype interactions

description: The outcomes of biological control programs can be highly variable, with
 natural enemies often failing to establish or spread in pest populations.
 This variability has posed a major obstacle in use of the bacterial
 parasite Pasteuria penetrans for biological control of Meloidogyne
 species, economically devastating plant-parasitic nematodes for which
 there are limited management options. A leading hypothesis for this
 variability in control is that infection is successful only for specific
 combinations of bacterial and nematode genotypes.  Under this
 hypothesis, failure of biological control results from the use of P.
 penetrans genotypes that cannot infect local Meloidogyne genotypes. We
 tested this hypothesis using isofemale lines of M. arenaria derived from a
 single field population and multiple sources of P. penetrans from the same
 and nearby fields. In strong support of the hypothesis, susceptibility to
 infection depended on the specific combination of host line and parasite
 source, with lines of M. arenaria varying substantially in which P.
 penetrans source could infect them. In light of this result, we tested
 whether using a diverse pool of P. penetrans could increase infection and
 thereby control. We found that increasing the diversity of the P.
 penetrans inoculum from one to eight sources more than doubled the
 fraction of M. arenaria individuals susceptible to infection and reduced
 variation in susceptibility across host lines. Together, our results
 highlight genotype-by-genotype specificity as an important cause of
 variation in biological control and call for the maintenance of genetic
 diversity in natural enemy populations.
description: <em><strong>Methods to collect the
 Data</strong></em> <em>Experiment 1:
 evaluating the significance of GxG interactions</em>
 The objective of this first experiment was to determine if
 attachment varies with the interaction of host line and parasite source.
 To do so, we measured attachment rate and load of J2s of four of our
 <em>P</em>. <em>penetrans</em> sources to our 13
 <em>M</em>. <em>arenaria</em> isofemale lines.
 Attachment rate is the percentage of nematodes with one or more endospores
 attached. This measurement captures variation between host-parasite
 combinations in the percentage of hosts susceptible to infection. To
 measure attachment rate, we counted the number of nematodes with and
 without endospores for an average of 17.45 ± 0.70 (standard error)
 nematodes per flask. A second measurement, attachment load, is the number
 of endospores attached per nematode. Attachment load is estimated only for
 hosts with one or more endospores attached. Thus, attachment load can
 capture variation between host-parasite combinations in the number of
 parasites that hosts acquire, given that a host line is susceptible to
 infection by a parasite source (i.e., attachment rate &gt; 0). To
 measure attachment load, we counted the number of endospores attached to
 the cuticle of up to 15 nematodes with endospores per flask.
 <em>Experiment 2: evaluating the effect of parasite
 diversity on infection probability  </em> The
 objective of this experiment was to determine if increasing parasite
 diversity increases attachment rate. We used all eight
 <em>P</em>. <em>penetrans</em> sources (Supplement
 2.3) and four host lines (H04, H08, H10, H13) that varied from low to high
 mean attachment rates in Experiment 1. We used the eight individual
 sources of <em>P</em>. <em>penetrans</em> as our
 low-diversity treatment (P01 – P08). We created a high-diversity parasite
 source (MIX) by combining equal volumes of soil from each of the eight
 individual sources. This approach created parasite treatments that varied
 qualitatively in diversity; we did not quantify the diversity of the high
 vs. low diversity treatments, because we did not perform genetic analyses
 of field-sampled parasite sources. We tested each host line against the
 eight low-diversity parasite sources and the high-diversity parasite
 source, inoculating with equal volumes of soil across diversity
 treatments. Each host-parasite combination was replicated in four flasks.
 We measured attachment rate and load as above.  Please
 find more details of the methods in the main manuscript and the
 supplemental material. 
 <em><strong>Data</strong></em> 
 The raw data collected from Experiment 1 is in the file
 <em>FM&AG_2022_Exp1.csv </em> The
 raw data collected from Experiment 2 is in the
 file <em>FM&AG2022_Exp2.csv</em>
 The other file is the Rscript for the whole analyses we did that
 are presented in the results of the manuscript.
 (<em>Rscript_FM&AG_2022EAFinal</em>)
description: The data files are saved in CSV. We used Excel to build the data
 set and R to analyse the data.