Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future

Synchronisation of the phenology of insect herbivores and their larval food plant is essential for the herbivores’ fitness. The monophagous brown hairstreak (Thecla betulae) lays its eggs during summer, hibernates as an egg, and hatches in April or May in the Netherlands. Its main larval food plant blackthorn (Prunus spinosa) flowers in early spring, just before the leaves appear. As soon as the Blackthorn opens its buds, and this varies with spring temperatures, food becomes available for the brown hairstreak. However, the suitability of the leaves as food for the young caterpillars is expected to decrease rapidly. Therefore, the timing of egg hatch is an important factor for larval growth. This study evaluates food availability for brown hairstreak at different temperatures. Egg hatch and budburst were monitored from 2004 to 2008 at different sites in the Netherlands. Results showed ample food availability at all monitored temperatures and sites but the degree of synchrony varied strongly with spring temperatures. To further study the effect of temperature on synchronisation, an experiment using normal temperatures of a reference year (T) and temperatures of T + 5°C was carried out in climate chambers. At T + 5°C, both budburst and egg hatch took place about 20 days earlier and thus, on average, elevated temperature did not affect synchrony. However, the total period of budburst was 11 days longer, whereas the period of egg hatching was 3 days shorter. The implications for larval growth by the brown hairstreak under a warmer climate are considered.

Top-Down Control of Herbivory by Birds and Bats in the Canopy of Temperate Broad-Leaved Oaks (Quercus robur)

The intensive foraging of insectivorous birds and bats is well known to reduce the density of arboreal herbivorous arthropods but quantification of collateral leaf damage remains limited for temperate forest canopies

Bottom-Up and top-down effects influence Bruchid beetle individual performance but not population densities in the field

Plant quality (bottom-up) and natural enemies (top-down) can influence the individual performance of herbivorous insects on their host plants, but few studies measured at the same time the influence on population densities in the field. We investigated if plant quality of different wild common bean populations, Phaseolus vulgaris L. (Fabaceae), affects the performance of the bean weevil, Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae), and one of its enemies, the ectoparasitoid Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae), in controlled laboratory experiments. Additionally, we examined if parasitoids influence the beetles' development and if increased individual beetle and parasitoid fitness lead to higher field population densities. We show that bean quality and parasitoids affected individual bean weevil performance under laboratory and field conditions. In the presence of parasitoids, fewer and smaller beetles emerged. However, beetle and parasitoid performance were not correlated. Increased individual performance was not leading to higher population densities; we found no correlations between measured performance components and beetle field infestation levels or parasitism rates. We conclude that bottom-up or top-down effects measured at the individual level do not always translate into population effects; therefore it is important to discriminate between effects acting on individual insects and those acting on populations

Spring warming increases the abundance of an invasive specialist insect: links to phenology and life history

Abstract Under global warming, shifts in phenological synchrony between insects and host plants (i.e., changes in the relative timing of the interaction) may reduce resource availability to specialist insects. Some specialists, however, can flexibly track the shifts in host-plant phenology, allowing them to obtain sufficient resources and therefore to benefit from rising temperatures. Here, we investigated the effects of experimental warming on the life history of an invasive, specialist lace bug (Corythucha ciliata) and on the leaf expansion of its host plant (Platanus × acerifolia) in two spring seasons under field conditions in Shanghai, China. We found that a 2 °C increase in mean air temperature advanced the timing of the expansion of host leaves and of the activities of overwintering adult insects in both years but did not disrupt their synchrony. Warming also directly increased the reproduction of overwintering adults and enhanced the development and survival of their offspring. These results indicate that C. ciliata can well track the earlier emergence of available resources in response to springtime warming. Such plasticity, combined with the direct effects of rising temperatures, may increase the insect’s population size and outbreak potential in eastern China under climate warming