Development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen forest in eastern China

Abstract The aim of this work was to understand the development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen broad-leaved forest in China. We measured the main developmental parameters of three typical defoliating insects （i.e., Ourapteryx ebuleata szechuana, Biston marginata, and Euproctis angulata） and their preferences for five host plants at temperatures from 16~C to 31 ~C at 3~C intervals in the Tiantong National Forest Research station in eastern China. The results showed the following. 1） An appropriate rise in temperature increases the survival rate with an increase in the number of offspring. The developmental durations for these three insects were shortened, and pupal weight increased with an increase in temperature. 2） A shift in the preference for host plants for these three insects was observedat elevated tempera- tures. They all preferred to feed on Schima superba and Castanopsis sclerophylla at elevated temperatures, show- ing an opposite response to the other three plants. The daily leaf consumption of the three insects was positively correlated with their feeding preference, with more leaves being consumed from the plants they preferred. 3） For O. ebuleata szechuana larvae, daily leaf consumption initially increased and then decreased with increasing temperatures. In contrast, Biston marginata and Euproctis angulata larvae consumed more leaves at elevated temperatures. The feeding preferences of O. ebuleata szechuana and Biston marginata were more sensitive to changing temperatures than that of Euproctis angulata laevae. We concluded that increased numbers of offspring and generations, pupal weights, and a shift in preference to two plants for these three defoliating insects might lead to severe damage to these two plants which would enhance the fragmentation and decrease the stability of the forest communities under changing temperatures. Meanwhile, the variations in the responses of defoliating insects to the changing temperatures should be taken into consideration for the pest management of forests to adapt to the changing climate.

Seed loss before seed predation: experimental evidence of the negative effects of leaf feeding insects on acorn production

Insect herbivory decreases plant fitness by constraining plant growth,survival and reproductive output.Most studies on the effects of herbivory in trees rely on correlational inter-individual comparisons and could,thus,be affected by confounding factors linked to both herbivory and plant performance.Using the Mediterranean Holm oak(Quercus ilex)as a study model,we followed an experimental approach in which leaf-feeding insects(mainly Lepidoptera caterpillars)were excluded from some shoots in all study trees.Shoots subjected to herbivore exclusion exhibited lower defoliation rates and produced more acorns than control shoots.Defoliation constrained shoot growth throughout the study period,but had no effect on the number of female flowers produced per shoot.Acorn production was,however,lower in control shoots due to their higher abortion rates,and also to their greater mortality risk during summer drought,as shoots with fewer leaves were less likely to survive.Plant reaction to herbivory inhibits certain physiological pathways involved in plant growth,which,together with the effects of physical damage,reduces the amount and efficiency of the photosynthetic tissue.This increases their vulnerability to environmental stresses,such as water deficit,which limit resource assimilation.Defoliation is likely a key factor affecting oak regeneration,as it may be a significant source of seed loss prior to pre-dispersal acorn predation.Further experimental studies could help to elucidate its effects in contrasting environments.In Mediterranean regions,the harsher droughts predicted by climate change models could worsen the effects of insect herbivory on oak reproductive output.