Effect of relative humidity and product moisture on response of diapausing and nondiapausing Indianmeal moth (Lepidoptera: Pyralidae) larvae to low pressure treatments

Humidity modifies species-specific and age-dependent heat stress effects in an insect host-parasitoid interaction

Climate change is projected to increase the frequency and intensity of extreme heat events, and may increase humidity levels, leading to coupled thermal and hydric stress. However, how humidity modulates the impacts of heat stress on species and their interactions is currently unknown. Using an insect host-parasitoid interaction: the Indian meal moth, Plodia interpunctella, and its endoparasitoid wasp, Venturia canescens, we investigated how humidity interacted with heat stress duration, applied at different host developmental stages, to affect life history traits. Hosts parasitized as 4th instar larvae and unparasitized hosts were maintained in high- (60.8% RH) or low-humidity (32.5% RH) at constant 28°C. They were then exposed to a 38°C thermal stress with a duration of 0 (no heat stress), 6 or 72 h in either the 4th or 5th host instar. Neither humidity nor heat stress duration affected emergence of unparasitized hosts, but increasing heat stress duration during the 4th instar decreased parasitoid emergence irrespective of humidity. When applied during the 5th instar, increasing heat duration decreased parasitoid emergence under low humidity, but no effect of heat stress was found under high humidity. Moreover, experiencing longer heat stress in the 4th instar increased host larval development time and decreased body size under high humidity, but this effect differed under low humidity; increasing heat duration in the 5th instar decreased parasitoid body sizes only under low humidity. Larval stage and heat stress duration directly affected parasitized host survival time, with a concomitant indirect reduction of parasitoid sizes. We show that humidity modifies key life history responses of hosts and parasitoids to heat stress in species-specific ways, highlighting the potential importance of humidity in regulating host-parasitoid interactions and their population dynamics. Finally, we emphasize that interactions between environmental stressors need to be considered in climate change research.

The Impacts of Climate Change on the Potential Distribution of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) in China

Simple Summary

Plodia interpunctella (Hübner) is an important grain storage pest in China that is distributed in almost every province and that has caused huge economic losses. In this study, we adjusted the biological parameters of the Indian grain borer and then used the CLIMEX model to predict the detailed potential distribution of P. interpunctella in China under current and future conditions. Under historical climatic conditions, the central, northeastern, and southern regions of China are highly suitable habitats for it. Because of temperature change in the future climate, suitable habitats will increase in the eastern part of Qinghai and will decrease in the mid-eastern, northeastern, and southeastern parts of China. This study provides important information for controlling the further spread of the Indian corn borer in China.

Abstract

The Indian meal moth Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) is a notorious stored-grain pest that can be found in most parts of China. The corpses, excretions, and other secretions of P. interpunctella larvae cause serious grain pollution, seriously affecting the nutritional and economic value of stored grain in China. To elucidate the potential distribution of P. interpunctella in China, we used the CLIMEX 4.0 model to project the potential distribution of the pest using historical climate data (1960–1990) and estimated future climate data (2030, 2050, and 2070). Under the historical climate situation, P. interpunctella was distributed in most areas of China, and its highly favorable habitats account for 48.14% of its total potential distribution. Because of temperature change in the future climate, suitable habitats will increase in the eastern part of Qinghai and will decrease in the mid-eastern, northeastern, and southeastern parts of China. Under these scenarios, the area of this pest’s highly favorable habitat will be reduced by 1.24 million km², and its proportion will decrease to about 28.48%. These predicted outcomes will help to distinguish the impact of climate change on the potential distribution of P. interpunctella, thereby providing important information to design early forecasting and strategies to prevent pest harm to stored grain.

Effects of Low Pressure Treatment on the Mortality of Different Life Stages of Indianmeal moth (Plodia interpunctella) and the Quality of Dried Chinese Jujube

Low pressure technology is a potential non-chemical method to control insects in agriculture products. The purpose of this study was to determine the tolerance of different life stages of indianmeal moth (Plodia interpunctella) to low pressure and to validate the mortality of P. interpunctella when infesting Chinese jujube (Zizyphus jujuba Miller) using a low pressure system. Results showed that larvae were the most tolerant life stage of P. interpunctella, with a minimum exposure time of 41.4 h at 1.3 kPa and 25 °C to obtain 100% mortality. Pupae were the most susceptible life stage, with a lethal time of 12 h under the above low pressure conditions. The survival ratio of P. interpunctella in jujube decreased with increasing exposure time and reached 0% when the jujubes with P. interpunctella larvae were exposed to low-pressure treatment for 41.6 h at 1.3 kPa and 25 °C. Although the color, moisture, soluble solid, and vitamin C contents were slightly changed, there was no significant quality difference in these factors between control and treated jujubes. The information provided by this study is useful in developing effective non-chemical low-pressure treatments for disinfesting agricultural products.

Barometric pressure influences host-orientation behavior in the larva of a dipteran ectoparasitoid

Rain and temperature have been awarded as the most important weather factors that influence insect behavior. Barometric pressure studies have been relegated to a secondary place mainly because most studies deal with adult insects where temperature and water availability are the main environmental factors that influence behavior. We studied the influence of barometric pressure on the host orientation behavior in Mallophora ruficauda, an ectoparasitoid with an active host-seeking larval stage. Our results show that a steeper decrease in barometric pressure than expected by regular variation reduced orientation to host chemical cues. This study is the first to show a correlation between changes in the barometric pressure and the seeking behavior of parasitoid soil-dwelling larvae. Our results show that in this kind of insects, ambient factors other than temperature, water availability and light, can influence and have a profound impact on the process of parasitism. We discuss the influence of this behavior on a task so important for parasitoids as host location, and highlight the importance of including such information in parasitoid foraging ecology and climatic change studies.

Comparative mortality of diapausing and nondiapausing larvae of Plodia interpunctella (Lepidoptera: Pyralidae) exposed to monoterpenoids and low pressure

Monoterpenoids and low pressure have each been demonstrated to cause mortality of stored-product insect pests. The current report investigated the prospects of integrating the two methods in the management of diapausing and nondiapausing larvae of Plodia interpunctella (Hübner). In a separate experiment, the larvae were exposed to 35.5 mmHg in Erlenmeyer flasks at 19 and 28 degrees C for times ranging from 30 min to 96 h. Another set of experiments was conducted to investigate the toxicity of exposing P. interpunctella larvae to monoterpenoids including E-anethole, estragole, S-carvone, linalool, L-fenchone, geraniol, gamma-terpinene, and DL-camphor alone or in combination with low pressure (50 mmHg). Lethal times (LT) determined by subjecting time-mortality data to probit analyses were shortened to half when both diapausing and nondiapausing larvae were exposed to low pressure at 28 degrees C compared with 19 degrees C. Exposure of diapausing larvae to a monoterpenoid alone, with the exception of DL-camphor and estragole, at a concentration of 66.7 microl/1L of volume required > 30 h to generate 99% mortality at 19.0 +/- 0.8 degrees C. However, the LT99 values for diapausing and nondiapausing larvae exposed to combinations of DL-camphor or estragole and low pressure were considerably shortened. Combinations involving the rest of the monoterpenoids investigated and low pressure did not generate LT99 that were shorter than those of the control, which was low pressure only. These results suggest that integrating low pressure with DL-camphor or estragole could be a new method for the control of diapausing larvae of P. interpunctella at cooler temperatures.

Response of Ceratitis capitata, Bactrocera dorsalis, and Bactrocera cucurbitae (Diptera: Tephritidae) to metabolic stress disinfection and disinfestation treatment

Metabolic stress disinfection and disinfestation (MSDD) is a postharvest treatment designed to control pathogens and arthropod pests on commodities that combines short cycles of low pressure/vacuum and high CO2 with ethanol vapor. Experiments were conducted to evaluate the effect of MSDD treatment on various life stages of Ceratitis capitata (Wiedemann), Mediterranean fruit fly; Bactrocera dorsalis Hendel, oriental fruit fly; and Bactrocera cucurbitae Coquillett, melon fly, in petri dishes and in papaya, Carica papaya L., fruit. In some experiments, the ethanol vapor phase was withheld to separate the effects of the physical (low pressure/ambient pressure cycles) and chemical (ethanol vapor plus low pressure) phases of treatment. In the experiments with tephritid fruit fly larvae and adults in petri dishes, mortality was generally high when insects were exposed to ethanol and low when ethanol was withheld during MSDD treatment, suggesting that ethanol vapor is highly lethal but that fruit flies are quite tolerant of short periods of low pressure treatment alone. When papaya fruit infested with fruit fly eggs or larvae were treated by MSDD, they produced fewer pupae than untreated control fruit, but a substantial number of individuals developed nonetheless. This suggests that internally feeding insects in fruit may be partially protected from the toxic effects of the ethanol because the vapor does not easily penetrate the fruit pericarp and pulp. MSDD treatment using the atmospheric conditions tested has limited potential as a disinfestation treatment for internal-feeding quarantine pests such as fruit flies infesting perishable commodities.