Do aphids in Dutch sweet pepper greenhouses carry heritable elements that protect them against biocontrol parasitoids?

Abstract

Biological control (biocontrol) of crop pests is a sustainable alternative to the use of biodiversity and organismal health‐harming chemical pesticides. Aphids can be biologically controlled with parasitoid wasps; however, variable results of parasitoid‐based aphid biocontrol in greenhouses are reported. Aphids may display genetically encoded (endogenous) defences that increase aphid resistance against parasitoids as under high parasitoid pressure there will be selection for parasitoid‐resistant aphids, potentially affecting the success of parasitoid‐based aphid biocontrol in greenhouses. Additionally, aphids may carry secondary bacterial endosymbionts that protect them against parasitoids. We studied whether there is variation in either of these heritable elements in aphids in greenhouses of sweet pepper, an agro‐economically important crop in the Netherlands that is prone to aphid pests and where pest management heavily relies on biocontrol. We sampled aphid populations in organic (biocontrol only) and conventional (biocontrol and pesticides) sweet pepper greenhouses in the Netherlands during the 2019 crop growth season. We assessed the aphid microbiome through both diagnostic PCR and 16S rRNA sequencing and did not detect any secondary endosymbionts in the two most encountered aphid species, Myzus persicae and Aulacorthum solani. We also compared multiple aphid lines collected from different greenhouses for variation in levels of endogenous‐based resistance against the parasitoids commonly used as biocontrol agents. We found no differences in the levels of endogenous‐based resistance between different aphid lines. This study does not support the hypothesis that protective endosymbionts or the presence of endogenous resistant aphid lines affects the success of parasitoid‐based biocontrol of aphids in Dutch greenhouses. Future investigations will need to address what is causing the variable successes of aphid biocontrol and what (biological and management‐related) lessons can be learned for aphid control in other crops, and biocontrol in general.

Common facultative endosymbionts do not influence sensitivity of cereal aphids to pyrethroids

“…The most common facultative endosymbionts detected in aphid populations are Spiroplasma spp ., Regiella insecticola , Hamiltonella defensa , Rickettsiella sp ., Fukatsia symbiotica (previously pea aphid x‐type symbiont, PAXS ), Serratia symbiotica , Rickettsia spp ., and Arsenophonus spp . (Beekman et al, 2022; Guo et al, 2017; Zytynska & Weisser, 2016). These facultative endosymbiotic relationships occur naturally in aphid populations (Beekman et al, 2022; Guo et al, 2019; Henry et al, 2015; Leybourne, Bos, et al, 2020).…”

Common facultative endosymbionts do not influence sensitivity of cereal aphids to pyrethroids

“…Successful DNA extraction was confirmed using a PCR marker for the primary aphid symbiont Buchnera aphidocola . The presence of facultative endosymbionts was determined using a three-step multiplex diagnostic PCR assay (Beekman et al ., 2022). Multiplex assays were used to detect the presence of the main aphid secondary endosymbionts: Spiroplasma spp., Regiella insecticola, Hamiltonella defensa, Rickettsiella sp., Fukatsuia symbiotica, Seratia symbiotica, Rickettsia spp ., and Arsenophonus spp .…”

“…The final reaction mixture was made to 12 μL using nuclease-free DEPC-treated water (CarlRoth, Germany). PCR conditions followed Beekman et al ., 2022, i.e. : denaturation at 94°C for 3 min followed by 35 cycles of 94°C for 30 s, 58°C for 30 s, and 72°C for 60 s with a final extension step at 72°C for 10 min.…”

Community diversity affects functionality and species sorting during propagation of a natural microbial community

“…Extracted DNA samples were stored at -20 °C. Extracted DNA was measured on Qubit using dsDNA High Sensitivity kit, and a new diluted sample made with DNA concentration 0.5 ng/µL.Nanopore MinIon protocol:Adapted from Beekman et al 2022(Beekman et al, 2022).DNA concentrations in these steps were always measured on Qubit 2.0 fluorometer using dsDNA High Sensitivity Assay kit (Thermo Fisher).Determination of number of PCR cycles:An approximate appropriate number of PCR cycles was first determined on just three samples (1-F1, 1-L1, 1-S1), using 13, 16, 18, and 25 cycles. Primers, amounts of reagents, and PCR settings were as described below in "Tailed PCR reaction".…”