Host choice, settling and folding leaf behaviors of the larval rice leaf folder under heat stress

Barometric pressure decrease induces density-dependent changes in foraging behaviour in a parasitoid fly

Barometric pressure is an environmental factor involved in the modulation of a variety of activities in insects. Generally, a drop in barometric pressure precedes the arrival of weather conditions that can affect insect activities and life expectancy. We simulated different scenarios of pressure drop in a modified hermetic chamber and studied their influence on the host-seeking behaviour of the larvae of the robber fly Mallophora ruficauda using air stationary olfactometers. In addition, we studied whether larval density modulates orientation to the host under the same scenarios of pressure drop. We found that motivation to search for hosts is affected by the same slope of pressure drop in both low- and high-density larvae. However, larval density modulates the onset of the responses to pressure decrease, as low-density larvae stop searching for hosts more quickly than high-density larvae. This result reflects an avoidance strategy according to which low-density larvae would have a reduced host range and higher risk of mortality and fewer chances to find a suitable host under adverse pressure conditions. Low-density larvae, known to prefer healthy hosts, do not search for parasitized hosts under normal pressure conditions nor under a range of pressure drops, strongly suggesting that host selectivity is not modulated by barometric pressure. This study paves the way to a better understanding of the changes in crucial insect behaviours induced by weather conditions, and provides more knowledge about the risk factors likely to affect insect survival in the context of foraging ecology.

Cuticular protein genes involve heat acclimation of insect larvae under global warming

Cuticular proteins (CPs) play important roles in insect growth and development. However, it is unknown whether CPs are related to heat tolerance. Cnaphalocrocis medinalis, a serious pest of rice, occurs in summer and exhibits strong adaptability to high temperature, but the underlying mechanism is unclear. Here, the role of CP genes in heat acclimation was studied. Heat tolerance of the heat-acclimated larvae was significantly stronger than the unacclimated larvae. The cuticular protein content in the heat-acclimated larvae was higher than that of the unacclimated larvae. 191 presumed CP genes of C. medinalis (CmCPs) were identified. Expression patterns of 14 CmCPs were different between the heat acclimated (S39) and unacclimated (S27) larvae under heat stress. CmCPs were specifically expressed in epidermis and the head except CmCPR20 mainly expressed in Malpighian tubules. CmCPR20 was upregulated in S39 while downregulated in S27, but CmTweedle1 and CmCPG1 were upregulated in S27 and downregulated in S39. RNAi CmTweedle1 or CmCPG1 remarkably decreased heat tolerance and cuticular protein content of the heat-acclimated larvae but not the unacclimated larvae. RNAi CmCPR20 decreased heat tolerance and cuticular protein content of the unacclimated larvae but not the heat-acclimated larvae. CmTweedle1 and CmCPG1 genes involve heat acclimation of C. medinalis.

Comparative transcriptome analysis of the rice leaf folder (Cnaphalocrocis medinalis) to heat acclimation

Background

The rice leaf folder Cnaphalocrocis medinalis Güenée is a serious insect pest of rice in Asia. This pest occurs in summer, and it is sensitive to high temperature. However, the larvae exhibit heat acclimation/adaptation. To understand the underlying mechanisms, we established a heat-acclimated strain via multigenerational selection at 39 °C. After heat shock at 41 °C for 1 h, the transcriptomes of the heat-acclimated (S-39) and unacclimated (S-27) larvae were sequenced, using the unacclimated larvae without exposure to 41 °C as the control.

Results

Five generations of selection at 39 °C led larvae to acclimate to this heat stress. Exposure to 41 °C induced 1160 differentially expressed genes (DEGs) between the heat-acclimated and unacclimated larvae. Both the heat-acclimated and unacclimated larvae responded to heat stress via upregulating genes related to sensory organ development and structural constituent of eye lens, whereas the unacclimated larvae also upregulated genes related to structural constituent of cuticle. Compared to unacclimated larvae, heat-acclimated larvae downregulated oxidoreductase activity-related genes when encountering heat shock. Both the acclimated and unacclimated larvae adjusted the longevity regulating, protein processing in endoplasmic reticulum, antigen processing and presentation, MAPK and estrogen signaling pathway to responsed to heat stress. Additionally, the unacclimated larvae also adjusted the spliceosome pathway, whereas the heat-acclimated larvae adjusted the biosynthesis of unsaturated fatty acids pathway when encountering heat stress. Although the heat-acclimated and unacclimated larvae upregulated expression of heat shock protein genes under heat stress including HSP70, HSP27 and CRYAB, their biosynthesis, metabolism and detoxification-related genes expressed differentially.

Conclusions

The rice leaf folder larvae could acclimate to a high temperature via multigenerational heat selection. The heat-acclimated larvae induced more DEGs to response to heat shock than the unacclimated larvae. The changes in transcript level of genes were related to heat acclimation of larvae, especially these genes in sensory organ development, structural constituent of eye lens, and oxidoreductase activity. The DEGs between heat-acclimated and unacclimated larvae after heat shock were enriched in the biosynthesis and metabolism pathways. These results are helpful to understand the molecular mechanism underlying heat acclimation of insects.

Effect of Steam Treatment on Feeding, Mating, and Fecundity of the Common Bed Bug (Hemiptera: Cimicidae)

Steam application is an effective and environmentally friendly method for controlling bed bugs, Cimex lectularius L. (Hemiptera: Cimicidae). While a few studies documented the bed bug control efficacy of steam treatment, the sublethal effect of steam treatment on bed bug behavior and female fecundity is unknown. In this study, we evaluated the effect of steam treatment on the movement, feeding, mating behavior, and fecundity of female bed bugs in the laboratory. Bed bug adults received a calibrated steam treatment that caused approximately 28% mortality. The surviving bed bugs were observed for their feeding and mating behavior at 1 d posttreatment, female fecundity during a 7-d observation period, and offspring hatching. Steam-treated bed bugs were less active based on the percentage of bed bugs with movement, moving distance during a 10-min observation period, and feeding rate. However, steam treatment had no significant effect on blood intake (amount of blood taken per meal) among the fed bed bugs. After blood feeding, the steam-treated bed bugs had similar mating events and egg production as the control bed bugs. Furthermore, parental steam exposure had no significant effect on the offspring hatching. In conclusion, steam treatment could temporarily decrease bed bug activity levels and feeding rate, but had no significant impact on bed bug mating behavior and female fecundity.

Climate change effects on predator-prey interactions

Predator-prey interactions can be very important to community structure and function. A growing body of research demonstrates how climate change can modify these species interactions. Climate change can modify predator-prey interactions by affecting species characteristics, and by modifying consumptive and/or non-consumptive predator effects. Current work examines how climate change and predation risk can combine to influence herbivore stoichiometry and feeding ecology. Other recent advances show how climate change can affect chemical signaling of plants and insects, as well as how pollution and other components of the environmental context can modify predator-prey interactions.

Can agricultural practices that mitigate or improve crop resilience to climate change also manage crop pests?

Sustainable agricultural practices that are promoted for mitigating climate change have the potential to also improve pest management. The author highlights recent studies that demonstrate effects of climate-mitigating agricultural practices on arthropod pests and predators in agronomic cropping systems. Promising practices for suppressing pests and/or improving biological control include: plant species diversification, especially via the addition of perennial species; cover cropping; tillage practices that retain crop residue; application of organic fertilizers such as compost and manure; and water management practices such as irrigation and sustainable rice intensification. More research is needed that explicitly tests pest and predator responses to agricultural practices under climate change conditions, if these practices are to be effectively promoted and implemented as agricultural pest management strategies.

Behavioural adaptation of the rice leaf folder Cnaphalocrocis medinalis to short-term heat stress

Under ongoing climate warming, both the degree and number of high-temperature events in summer may increase, and behavioural adaptation is an important ecological strategy employed by insects to cope with such events. The rice leaf folder, Cnaphalocrocis medinalis Güenée, is a serious insect pest of rice fields in summer. Population outbreaks have become more frequent in the last ten years. In addition to adult migration, rice leaf folders are thought to have other thermal adaptations. Therefore, the behaviours of larval and adult rice leaf folders, such as leaf folding (making shelter) and habitat selection for pupae and eggs, were observed on rice plants under heat stress. The results showed that larval shelter-making velocities significantly decreased during or after four hours of heat exposure, and shelter size decreased as the temperature increased. Larvae preferred to pupate on young rice leaves at 27°C and middle-aged leaves at 30°C, but they strongly preferred older leaves when reared at 34°C. Female moths generally preferred to oviposit on the top of young leaves, but they preferred the middle and lower leaves for egg deposition when exposed to 36 and 40°C, respectively. Furthermore, more eggs were distributed on the lower surfaces of rice leaves with an increase in heat stress. These behavioural responses of rice leaf folders to heat stress indicate that this pest has great potential to adapt to high temperatures; therefore, the possibility of a population outbreak will remain high despite global warming.