Abstract:1. Plant genotype influences plant-herbivore interactions by affecting insect attraction, acceptance and development. Here we linked oviposition behaviour of the specialist willow sawfly Nematus oligospilus Förster (Hymenoptera: Tenthredinidae) with leaf traits on different Salix L. (Salicaceae) genotypes. This was done as a first step to find oviposition cues that guide females to their host plants.2. By means of choice and no-choice bioassays we analysed host selection according to willow genotype and leaf s… Show more
“…Landau’s Linearity Index was near 1 which indicates a hierarchy completely linear 37 . As expected from previous observations 17,24 and these data, the willow hybrid containing S. nigra (‘Lezama’) was the most preferred, with the highest David Score, which means that it always received more eggs in the comparisons. ‘Géminis’ was the least preferred hybrid with a David Score of 1 (this hybrid was never preferred against the others).Figure 6Natural colonization and oviposition preference in six different commercial willow hybrids.…”
After an insect herbivore has reached its host plant, contact cues from the leaf surface often determine host acceptance. We studied contact cues during oviposition behavior of a willow pest, the sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae), a specialist feeder on Salix (Salicaceae) trees, and how it determines oviposition preference in lab and field conditions. We described the sequence of behaviors that lead to egg laying on the most and least preferred willow species. Then we studied the morphology of chemosensory structures present on the female antenna, cerci and ovipositor. Since phenolic glycosides (PGs) are the main secondary metabolites present in Salicaceae species, we investigated their role in host acceptance. We quantified these compounds in different willow species and correlated PG content with oviposition preference under lab and natural field conditions. We demonstrated a major role for contact cues in triggering N. oligospilus egg laying on the leaf surface of preferred willow genotypes. Firstly cues are sensed by antennae, determining to leave or stay on the leaf. After that, sensing is performed by abdominal cerci, which finally triggers egg laying. The lack of PGs in non-preferred species and the significant correlation observed between PGs, natural damage and oviposition preference suggest a role for these compounds in host selection. Our study suggests that in specialist feeders, secondary compounds normally acting as defenses can actually act as a susceptibility factor by triggering specific insect behavior for oviposition. These defensive compounds could be selected against to increase resistance.
“…Landau’s Linearity Index was near 1 which indicates a hierarchy completely linear 37 . As expected from previous observations 17,24 and these data, the willow hybrid containing S. nigra (‘Lezama’) was the most preferred, with the highest David Score, which means that it always received more eggs in the comparisons. ‘Géminis’ was the least preferred hybrid with a David Score of 1 (this hybrid was never preferred against the others).Figure 6Natural colonization and oviposition preference in six different commercial willow hybrids.…”
After an insect herbivore has reached its host plant, contact cues from the leaf surface often determine host acceptance. We studied contact cues during oviposition behavior of a willow pest, the sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae), a specialist feeder on Salix (Salicaceae) trees, and how it determines oviposition preference in lab and field conditions. We described the sequence of behaviors that lead to egg laying on the most and least preferred willow species. Then we studied the morphology of chemosensory structures present on the female antenna, cerci and ovipositor. Since phenolic glycosides (PGs) are the main secondary metabolites present in Salicaceae species, we investigated their role in host acceptance. We quantified these compounds in different willow species and correlated PG content with oviposition preference under lab and natural field conditions. We demonstrated a major role for contact cues in triggering N. oligospilus egg laying on the leaf surface of preferred willow genotypes. Firstly cues are sensed by antennae, determining to leave or stay on the leaf. After that, sensing is performed by abdominal cerci, which finally triggers egg laying. The lack of PGs in non-preferred species and the significant correlation observed between PGs, natural damage and oviposition preference suggest a role for these compounds in host selection. Our study suggests that in specialist feeders, secondary compounds normally acting as defenses can actually act as a susceptibility factor by triggering specific insect behavior for oviposition. These defensive compounds could be selected against to increase resistance.
“…et al 2019. These results are also in agreement with our previous studies (Braccini et al, 2013(Braccini et al, , 2015 reinforcing the idea that orientation of N. oligospilus females on Salix spp. is driven by volatile cues and final decision for egg laying is determined by a balance among leaf structure, plant nutrients and secondary metabolites.…”
Section: Discussionsupporting
confidence: 93%
“…Females of this species are parthenogenetic in the Southern Hemisphere and emerge sexually mature. Upon emergence, females forage alone and lay individual eggs under the cuticle or first layer of epidermal cells of willow leaves (Braccini et al ., 2013). Due to the low larval mobility, after hatching the larva starts its development on the leaf where its mother laid the egg.…”
AbstractThe willow sawfly, Nematus oligospilus (Förster), is a pest in Salix commercial forests and has been reported worldwide. Female adults must recognize a suitable host plant to oviposit, since her offspring lack the ability to move to another host. We evaluated the effect of conspecific herbivory on the oviposition choices of N. oligospilus females by providing damaged (DP) and undamaged (UP) plants of Salix humboldtiana, a native willow from South America, as oviposition substrates. Local and systemic effects were studied. For the local treatment, a twig from the DP with damaged leaves was contrasted to a twig from a UP in dual choice experiments. For systemic treatment, a twig from the DP with intact leaves was contrasted to a twig from a UP. We estimated the use of olfactory and contact cues by comparing volatile emission of DP and UP, and by analysing the behaviour of the females during host recognition after landing on the leaf surface. In the context of the preference–performance hypothesis (PPH), we also tested if oviposition site selection maximizes offspring fitness by evaluating neonate hatching, larval performance and survival of larvae that were born and bred on either DP or UP. Our results demonstrate that previous conspecific herbivory on S. humboldtiana has a dramatic impact on female oviposition choices and offspring performance of the sawfly N. oligospilus. Females showed a marked preference for laying eggs on UP of S. humboldtiana. This preference was found for both local and systemic treatments. Volatile emission was quantitatively changed after conspecific damage suggesting that it could be related to N. oligospilus avoidance. In the dual choice preference experiments, the analysis of the behaviour of the females once landing on the leaf surface suggested the use of contact cues triggering egg laying on leaves from UP and avoidance of leaves from DP. Furthermore, 48 h of previous conspecific feeding was sufficient to dramatically impair neonate hatching, as well as larval development and survival, suggesting a rapid and effective reaction of the induced resistance mechanisms of the tree. In agreement with the PPH, these results support the idea that decisions made by colonizing females may result in optimal outcomes for their offspring in a barely studied insect model, and also opens the opportunity for studying tree-induced defences in the unexplored South American willow S. humboldtiana.
“…Other sawfly species use secondary metabolites in the selection of their host plant, such as Euura amerinae (L.) and Euura lasiolepis Smith, monophagous species that recognize and select their Salix host plants based on characteristic phenolic glycosides (Kolehmainen, ; Roininen et al., ). Host plant parameters not considered in the present study – such as leaf hardness, leaf surface, and plant volatiles – may also affect sawfly oviposition preferences (Buteler & Weaver, ; Braccini et al., ; Varella et al., ). They deserve further investigation in our study system.…”
Section: Discussionmentioning
confidence: 99%
“…Finally, most preference–performance research has been carried out on lepidopteran species, possibly skewing the information (Gripenberg et al., ). Other groups of insects, such as the hymenopterans, have been infrequently studied in this regard, comprising only the families Tenthredinidae and Cephidae of the Symphyta suborder and showing inconsistent results in preference–performance correlations (Roininen & Tahvanainen, ; Price et al., ; Nagasaka & Ohsaki, ; Ferrier & Price, ; Digweed, ; Perez‐Mendoza et al., ; Müller & Arand, ; Buteler et al., ; Braccini et al., ).…”
In herbivorous insects, the preference–performance hypothesis predicts that females will choose to oviposit on plants that maximize offspring development. Although there is evidence to support this hypothesis, several studies have shown that it does not always apply. Among the factors that may modulate the preference–performance relationship, diet breadth is a significant one, although no correlation has been found for monophagous insects. More case studies are needed, as more restricted diets are expected to require better discrimination ability. In this study, we explored the preference–performance linkage in a monophagous sawfly, Tequus schrottkyi (Konow) (Hymenoptera: Pergidae), which feeds as larva on the wild potato Solanum commersonii Dunal (Solanaceae). We used the cultivated potato, Solanum tuberosum L., as an alternative host plant for our experiments. Performance was evaluated from newly emerged larvae until adult emergence, raising individual larvae on potted plants or excised leaves. Female oviposition preference was studied in two‐choice bioassays, in which individual females were offered whole plants of S. commersonii and S. tuberosum. The nutritional quality of the plants was assessed by measuring protein, non‐structural carbohydrate, and water contents. The offspring performed better on their host plant, S. commersonii, resulting in more larvae completing their development to the adult stage. Moreover, the larvae developed faster and their cocoon weighed more when they were raised on their host plant. The females oviposited almost exclusively on S. commersonii, regardless of their previous food plant. The protein and non‐structural carbohydrate contents did not differ between the plants, whereas water content was higher in the non‐preferred S. tuberosum. The differences in water content and in secondary metabolites, which have been analyzed in a previous study, may play a role in female preference and offspring performance. The results are discussed within the framework of the preference–performance hypothesis and the chemical ecology of insect–plant interactions.
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