Evolutionary, physiological and phenological responses of Spodoptera frugiperda to climate change
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Date
2023
Authors
Mbande, Abongile
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
The threat of biological invasions due to global climate change and anthropogenic activities is growing globally. Environmental changes, such as increasing mean temperatures due to global climate warming, may exacerbate the spread of invasive insect species by improving their voltinism, survival, reproductive success and geographic range expansion. The fall armyworm (FAW) Spodoptera frugiperda is one of the most economically important invasive insect pests attacking sub-Saharan Africa (SSA) staple crops, such as maize and sorghum. First reported in West Africa in 2016, FAW has spread to the rest of SSA. Key questions arising from this rapid geographic expansion is how climate and its physiological attributes aid its invasion potential. This is particularly important in this era of global climate change where phenological mismatches are known to also influence their host utilization and survival across different life-stages and physiological status such as mating or feeding. Evolutionary responses at individual and population also play a pivotal role in survival and population persistence across various temporal scales. This study explored the evolutionary, physiological and phenological responses of S. frugiperda to climate change. First, I measured the effects of short-term exposure to heat shock on physiological responses vis critical thermal limits (critical thermal minima [CTmin] and critical thermal maxima [CT max]), and ecological traits vis reproductive success (fecundity [number of eggs per female] and hatching success) and longevity using virgin adults following heat shock at 32, 35, and 38 °C for 2 hours. Second, I assessed the effects of repeatable exposure to cold (CTmin) and chill coma recovery time (CCRT) for 0; 24; 48 and 72 hours and the body lipid content (BLC) and body water content (BWC) on adult fall armyworm (24 h old). Last, I investigated the thermal tolerance of S. frugiperda at 3, 6 and 9 days old adults heat shocked at adult, pupal and larval stages, at 40℃ for 2 hours. Heat shock improved tolerance to heat (measured as CTmax) but negatively affected cold tolerance (measured as CTmin). Males were more vulnerable to heat stress than females. Interestingly, heat shock also reduced fecundity, hatching success and adult longevity. Cold tolerance measured as CTmin improved with repeated exposure in 5th instar larvae, virgin males, and females while CCRT improved in 4th, 5th and 6th instar larvae following repeated cold exposure. Heat tolerance in virgin females showed highest CTmax in 6 day olds while it fluctuated in males. Mated males had higher CTmax than mated females across all heat shocked developmental stages. This study shows that, under heat stress, reproductive fitness in FAW is largely compromised due to low fecundity and stress resistance that is dependent on mating status, age and life-stage. Taken together, the results show that thermal variation has fitness consequences for FAW at both individual and population level. These results provide valuable data that inform mechanistic models for the geographic distribution of FAW under variable climate scenarios. This will especially be critical in developing early warning systems and area-wide strategies for FAW control.
Description
Thesis (Ph.D.(Entomology))--University of the Free State, 2023
Keywords
Environmental stress, invasive species, longevity, population persistence, reproductive fitness, trade-off, thermal tolerance