Temperature-dependent oviposition and nymph performance reveal distinct thermal niches of coexisting planthoppers with similar thresholds for development

Abstract

The brown planthopper (Nilapavata lugens: BPH) and whitebacked planthopper (Sogatella furcifera: WBPH) co-occur as the principal pests of rice in Asia. A review of previous studies suggests that the two species have similar temperature tolerances and similar temperature thresholds for development. However, the distribution and seasonality of WBPH suggest that its temperature optima for performance (survival, oviposition and growth) may be lower than for BPH. We compared adult longevity, oviposition, nymph survival and development success, as well as nymph biomass in both species across a gradient of constant temperatures from 15˚C-40˚C, at 5˚C intervals. The most suitable temperatures for oviposition, nymph biomass and development success were 5-10˚C lower for WBPH than for BPH. Furthermore, compared to BPH, WBPH demonstrated clear differences in oviposition on different rice subspecies and on rice at different growth stages at 25˚C and 30˚C, but not at other temperatures. The results suggest that aspects of herbivore performance within tolerable temperature ranges, which are not often included in temperature models, may be more useful than thermal tolerances or development thresholds in predicting the effects of global warming on pest damage to crops.

Intraspecific competition counters the effects of elevated and optimal temperatures on phloem-feeding insects in tropical and temperate rice

“…WBPH nymphs had higher survival, more rapid development and attained a greater biomass at 25°C compared to 30°C. Nymphs of both species failed to develop to adults at 35°C possibly due to adverse effects of the high temperature on yeast-like endosymbionts, which are essential for nymph nutrition [ 18 , 40 – 42 ]; but also due to the comparatively slow growth of rice plants at 35°C. Adult BPH produced more eggs at 30°C than at 25 or 35°C.…”

“…Contrary to expectations, WBPH females produced more eggs at 35°C than at other temperatures during our experiments. However, a previous study has shown that WBPH adult longevity is severely reduced at 35°C and, consequently, life-time fecundities are generally lower at 35°C than at 25 or 30°C (egg-laying was similar at 25 and 30°C) [ 18 ]. We suggest that the high rate of oviposition in WBPH at 35°C was a stress response.…”

“…Population regulation by natural enemies [ 37 , 47 , 48 ] and ontogenic changes in rice susceptibility [ 46 ] also contribute to the decline of WBPH populations during crop maturation. Our results indicate that current ambient temperatures in tropical Asia, that frequently surpass 30°C during extended periods [ 18 , 41 ], will reduce the potential for WBPH to attain outbreak densities.…”

“…Nymphs were allowed to feed and develop for 15 days. Previous experiments using the same planthopper colonies and rice varieties have indicated that nymphs of both species will develop to adults in ≤ 10 days at temperatures of 25–30°C; nymphs will not develop to adults at 35°C [ 18 ]. After 15 days, the survivors were collected by tapping the cages over funnels into glass vials.…”

“…The lowest temperature used in our experiments (25°C) was about optimal for WBPH oviposition and development. Higher temperatures were included among the optimal temperatures for BPH (i.e., 25–30°C) or were close to the critical upper temperature limits for eggs and nymphs of both species (35°C) [ 18 , 34 , 35 ]. We predicted that intraspecific competition would be more intense (i.e., cause greater reductions in the fitness of individuals) under the optimal temperatures for each planthopper species and that this would counter the positive effects of optimal and elevated temperatures on the planthoppers.…”