Developmental stage-dependent response and preference for host plant quality in an insect herbivore

Abstract

Larval-derived nutritional reserves are essential in shaping insects' adult fitness. Early larval instars of many Lepidopteran species are often sessile, and the conditions experienced by these larvae are often highly dependent on the mother's oviposition choice. Later larval stages are more mobile and therefore can choose their food whenever alternatives are available. We tested how feeding on a drought-exposed host plant impacts life history in an insect herbivore, and whether the observed responses depended on developmental stage. We used drought to alter host plant quality of the ribwort plantain, Plantago lanceolata , and assessed whether host plant preference of postdiapause larvae and adult females increased their own or their offspring's performance, respectively, in the Glanville fritillary butterfly, Melitaea cinxia . Larval response to drought-exposed host plants varied with developmental stage: early larval stages (prediapause) had decreased survival and body mass on drought-exposed plants, while later larval stages (postdiapause) developed faster, weighed more and had a higher growth rate on the drought-exposed plants. Postdiapause larvae also showed a preference for drought-exposed host plants, i.e. those that increased their performance, but only when fed on well-watered host plants. Adult females, on the other hand, showed an oviposition preference for well-watered plants, hence matching the performance of their prediapause but not their postdiapause offspring. Our results highlight how variation in environmental conditions generates stage-specific responses in insects. Individuals fine-tune their own or their offspring's diet by behavioural adjustments when variation in host plant quality is available.

Every cloud has a silver lining: Moderate plant water stress positively impacts development, immunity, and gut microbiota of a specialist herbivore

“…To conclude, we found mostly beneficial effects of moderate plant drought-stress on insect performance, indicating that the previously suggested negative impact of reduced precipitation is likely due to extreme desiccation [22,34]. Indeed, this pattern is confirmed by work finding reduced survival and body mass of larvae fed on severely water-stressed plants [34].…”

“…In general, our findings suggest a higher larval performance on moderately water-stressed plants. Intriguingly, larvae of the same age but faced with severe plant water stress have a low performance in terms of both reduced survival and body mass [34].…”

Long‐term demographic surveys reveal a consistent relationship between average occupancy and abundance within local populations of a butterfly metapopulation

“…The effects on occupancy are limited to large-scale annual differences with limited spatial variation, while for abundance the effects are more variable and also more local due to, for example, behavioural interactions with the local topography and microclimate (Eilers et al 2013, Lawson et al 2014. Any effects on abundance will also have indirect impacts on occupancy: for example, if summer drought reduces the quantity and quality of host plant available for larvae, the consequent reduction in abundance would also increase extinction risk in the next year (Salgado and Saastamoinen 2019).…”

Narrow oviposition preference of an insect herbivore risks survival under conditions of severe drought

“…nest presence showed significant negative relationships with PC1 and PC2) in addition to sites with higher host plant coverage and drought stress, neither PC1 nor PC2 were found to be related to overwintering survival. Finally, we have some experimental evidence that suggests that feeding on drought exposed host plants does, at least in some families, directly increase larval performance (pre-diapause larvae: Rosa et al 2019 & post-diapause larvae: Salgado & Saastamoinen, 2019) that seems to even translate to increased adult performance (Salgado & Saastamoinen, 2019). Even though the impact of drought on host plant quality was not assessed here, previous studies on other systems have shown that plants under drought stress often accumulate nutrients, such as carbon and nitrogen, that can enhance the performance of insect herbivores (Gutbrodt, Mody, & Dorn, 2011;Mattson & Haack, 1987).…”

“…Hanski et al, 2017;Schulz, Vanhatalo, & Saastamoinen, 2019) and combine it with detailed field assessments to ask whether oviposition preferences vary across years and whether mothers generally choose locations that enhance their offspring's overwinter survival. As Finland is the northern range limit of these butterfly species, with relatively short time window for larval development, and based on our recent findings that larval performance may be increased by feeding on droughtexposed host plants (Rosa, Minard, Lindholm, & Saastamoinen, 2019;Salgado & Saastamoinen, 2019), we hypothesize that drier microhabitats are generally favoured by the females but may be disadvantageous for the larvae during particularly warm and dry years.…”