Effects of Larval Rearing Temperature and Host Plant Condition on the Development, Survival, and Coloration of African Armyworm, Spodoptera exempta Walker (Lepidoptera: Noctuidae)

Abstract

Effects of temperature and host plant condition on insect development have been examined in a number of studies but their combined effect is not well investigated. In this study the effects of varying temperatures and host plant conditions and its interaction on development, survival, and coloration of solitarious and gregarious forms of African armyworm (AW), Spodoptera exempta, an outbreak pest species, were studied under laboratory condition. Rearing temperature was found to have significant effects on larval and pupal development and pupal weight in both solitarious and gregarious forms. The effects of host plant condition in both forms were variable; significant effects were consistently observed in pupal development for both gregarious and solitarious forms but not in larval development and pupal weight. Larval and pupal survival of the solitarious form significantly decreased with the decreased in temperature, while only pupal survival decreased with the decreased in temperature in gregarious form. Distinct larval coloration was also observed in different temperatures. Larvae reared at high temperature exhibited lighter coloration, while larvae reared at low temperature exhibited darker coloration regardless of rearing density. The significant interaction of temperature and host plant condition on many aspects of insect fitness measured in this study highlights the need for further studies on the effects of other environmental factors such as relative humidity, rainfall, and light intensity to improve predictions as to how these insect pests will respond to climate change.

Predicting potential global and future distributions of the African armyworm (Spodoptera exempta) using species distribution models

“…Nonetheless, the areas where outbreaks occur (which we modelled) are not always the same as the ones where low-density populations settle (which we did not explicitly model). Temperature changes affect the species distribution too because, being ectotherms, their development and survival are temperature-dependent 56 .…”

“…2 A). Low environmental suitability coincides with arid or semi-arid areas, which may seem evident as extreme temperatures and dry conditions are not ideal for the development of its eggs and pupae 56 , 57 . Indeed, water and ambient humidity scarcity can affect the water balance of insects, impacting their survival, development and even their population dynamics, as seen in similar species, the FAW 58 .…”

BIOLOGY AND MORPHOMETRICS OF THE FALL ARMYWORM, Spodoptera frugiperda J. E. SMITH (LEPIDOPTERA: NOCTUIDAE) IN IBADAN, SOUTHWEST NIGERIA

“…(2020) reported total larval development periods in the 10 to 14 days range (average of 11.38 ± 0.25 days) at 30 o C, and between 10 to 12 days at 32 o C. Temperature greatly influences the rate of development, and by extension, the biology, occurrence, abundance, and distribution of insect pests (Howe, 1967;Porter, 1991;Tobin et al, 2003;Abrahams et al, 2017;Du Plessis et al, 2020). In the same vein, the number of instars comprising an insect larval stage is significantly influenced by rearing temperature and diet (Ali et al, 1990;Aguilon et al, 2015;Rojas et al, 2018). Furthermore, S. frugiperda larva developed through six instars on natural maize leaf diet at an ambient temperature of approximately 30 o C. Du Plessis et al (2020) also reported an optimum temperature of 30 o C for the development of S. frugiperda larvae, even though it may range between 26 -30 o C. Sharanabasappa et al (2018) reported a 9 -12 days pupation period for S. frugiperda in India.…”

Effects of temperature on monarch caterpillar pigment variation in nature

“…Temperature in particular appears to have clear effects on intraspecific variation in lepidopteran colouration (Hill et al, 2021). Higher growing temperatures resulted in lighter colouration in African armyworm ( Spodoptera exampta ) larvae, Asian comma ( Polygonia caureum ) pupae and speckled wood ( Parage aegeria ) adults (Aguilon et al, 2015; Taylor‐Cox et al, 2020; Yamanaka et al, 2012). Similarly, monarch larvae reared in the laboratory at warmer temperatures displayed thinner black stripes compared to those reared at colder temperatures (Davis et al, 2005; Solensky & Larkin, 2003).…”