The nocturnal larvae of a specialist folivore perform better on Chromolaena odorata leaves from a shaded environment

Abstract

Increasing evidence suggests that individuals of the same plant species occurring in different microhabitats often show a degree of phenotypic and phytochemical variation. Consequently, insect herbivores associated with such plant species must deal with environment-mediated changes or variability in the traits of their host plants. In this study, we examined the effects of habitat condition (shaded vs. full-sun habitats) on plant traits and leaf characteristics of the invasive alien plant, Chromolaena odorata (L.) King & Robinson (Asteraceae). In addition, the performance was evaluated in two generations of a specialist folivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), on leaves obtained from both shaded and full-sun habitats. The study was done in an area where the insect was introduced as a biological control agent. Leaves growing in shade were less tough, had higher water and nitrogen content, and lower total non-structural carbohydrate, compared with leaves growing in full sun. Plants growing in shade had longer leaves and were taller, but aboveground biomass was significantly reduced compared with plants growing in full sun. In both generations (parents and offspring), P. insulata developed faster and had larger pupal mass, increased growth rate, and higher fecundity when reared on shaded foliage compared with full-sun foliage. Although immature survival and adult longevity did not differ between habitats, Maw's host suitability index indicated that shaded leaves were more suitable for the growth and reproduction of P. insulata. We suggest that the benefits obtained by P. insulata feeding on shaded foliage are associated with reduced toughness and enhanced nitrogen and water content of leaves. These results demonstrate that light-mediated changes in plant traits and leaf characteristics can affect insect folivore performance.

Developmental and reproductive performance of a specialist herbivore depend on seasonality of, and light conditions experienced by, the host plant

“…(Solanaceae). Light intensity (measured by a light meter, LX–101, Taiwan) differed significantly between the two habitats in autumn (mean ± SE: 1872.17 ± 23.36 and 347.21 ± 20.22 lux for full-sun and shaded habitat respectively; GLM ANOVA, F 1,19 = 2436.82, P < 0.0001) and winter (mean ± SE: 1882.10 ± 34.251 and 358.23 ± 14.87 lux for full-sun and shaded habitat respectively; GLM ANOVA, F 1,19 = 921.243, P < 0.0001) (see Uyi et al [ 19 ] for further details about the study site). The leaf characteristics and insect performance study were conducted in winter/early spring 2013 (from July 15 th to October 6 th , 2013 = winter trial) and late summer/autumn 2014 (from March 11 th to June 4 th , 2014 = autumn trial) as a comparison, while the larval preference trial was conducted in early winter 2017 (6-8 th June 2017).…”

“…The specific leaf weight (SLW), which provides a physiological estimate of ‘leaf toughness’ [ 37 ] of 100 fully expanded leaves (taken from the upper half of the plants) obtained from 20 plants per habitat type (5 leaves per plant) in August 2013 (winter) and April 2014 (autumn) was estimated in both shaded and full-sun habitats following the methods described in our earlier study [ 19 ]. Different 20 plants were sampled in August 2013 and April 2014.…”

“…In nature, individuals of the same species growing in different light environments (e.g. shaded vs full-sun habitats) often exhibit a degree of phenotypic and phytochemical variation [ 12 , 18 , 19 ] primarily because light intensity directly influences the physiological, growth and biochemical processes in plants by directly controlling carbon intake through photosynthesis [ 13 , 20 , 21 ]. The carbon/nutrient balance (C/NB) hypothesis [ 22 , 23 , 24 ] postulates that leaves of plants growing under sub-optimal levels of photosynthetically active radiation (e.g.…”

“…Previous studies, including ours, that evaluate the performance of insect herbivores on foliage from full-sun versus shaded environments, infrequently consider seasonality and host plant phenology or conduct such investigations at only one point in time [ 8 , 18 , 19 ]. The phenology of C .…”

Reduced mobility but high survival: thermal tolerance and locomotor response of the specialist herbivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae), to low temperatures

“…Late 5th and 6th instars of P. insulata migrate down the base of the C. odorata plants and pupate in a flimsy cocoon in the leaf litter. Development time from larva to adult (at 25°C) usually ranges from 26 to 42 days depending on food quality (Uyi et al, 2014b(Uyi et al, , 2015.…”