Abstract
Climate change will have a noteworthy bearing on survival, development, and population dynamics of insect pests. Therefore, we contemplated the survival and development of beet army worm, Spodoptera exigua under different temperatures, (15˚C, 25˚C, 35˚C, and 45˚C), CO2 (350, 550, 750 ppm) and relative humidity (55%, 65%, 75% and 85%) regimes. Maximum larval and pupal weights were recorded in insects reared at 25˚C. The growth of S. exigua was faster at 35˚C (larval period 7.4 days and pupal period 4.5 days) than at lower temperatures. At 15˚C, the larval period was extended for 61.4 days and there was no adult emergence from the pupae till 90 days. The S. exigua hatchling was absent at 45˚C. The larval survival ranged from 31.6% - 57.2%, maximum survival was recorded at 25˚C, and minimum at 45˚C. The maximum (84.27%) and minimum adult emergence were recorded in insects reared at 25˚C and 35˚C respectively. Maximum fecundity (384.3 eggs/female) and egg viability (51.97%) were recorded in insects reared at 25˚C. Larval and pupal periods increased with an increase in CO2 concentration. The highest pupal weights (128.6 mg/larva) were recorded at 550 ppm. The highest larval survival (73.50%) was recorded at 550 ppm and minimum (37.00%) at 750 ppm CO2. Fecundity was the highest in insects reared at 550 ppm CO2 (657.4 eggs/female), and the lowest at 750 ppm. Maximum larval and pupal weights were recorded in insects reared at 75% relative humidity (RH). The growth rate of S. exigua was faster at 85% RH than at lower RH. The larval survival ranged between 40.0% - 58.5%. Maximum adult emergence (88.91%) was recorded in insects reared at 75% RH and minimum at 85% RH. Maximum fecundity (447.6 eggs/female) and the highest egg viability (72.95%) were recorded in insects reared at 75% and 65% RH respectively. Elevated temperatures and relative moistness will diminish the life cycle, while hoisted CO2 will drag the life expectancy. Therefore, there is a need for thorough assessment of the impact of climatic factors on the population dynamics of insect pests, crop losses, and sustainability of crop production.
Highlights
The fifth estimation report of the Inter-Governmental Panel on Climate Change (IPCC Climate Change 2014) reconfirmed that the globally averaged combined land and ocean surface temperature data as calculated by a direct pattern, show a warming of 0.85 ̊C [0.65 ̊C to 1.06 ̊C] over the period of 1880 to 2012
The data from effect of climatic parameters on growth and development viz., larval weight, larval duration, pupal weight, pupal duration, percent survival and adult emergence of S. exigua were subjected to analysis of variance using GenStat 13th edition, while the significance of differences between the genotypic means was judged by the least significant difference at P = 0.05
Effect of CO2 on survival and development of beet armyworm, S. exigua Larval weights after 10 days of infestation across different levels of CO2 ranged from 240.0 - 272.7 mg and the detailed summary is presented in (Table 4)
Summary
The fifth estimation report of the Inter-Governmental Panel on Climate Change (IPCC Climate Change 2014) reconfirmed that the globally averaged combined land and ocean surface temperature data as calculated by a direct pattern, show a warming of 0.85 ̊C [0.65 ̊C to 1.06 ̊C] over the period of 1880 to 2012. The most predicted effects of climate change, i.e., the increase in temperature and CO2 concentration will have a significant effect on agriculture in general and on herbivore insect populations in particular. Measurement of the connection between insect advancement and temperature is fundamental to foresee populace elements of the insect pests This increase is likely to affect biota indirectly via climate change, and directly by producing changes in plant growth and allocation, and in plant tissue chemical composition. The role of host plants, in particular food limitation, is important in regulating insect populations (Umbanhowar & Hastings, 2002) as the life-history traits of herbivores may be influenced by variation in host-plant characteristics (Awmack & Leather, 2002). The present studies were conducted under controlled growth chamber in order to predict the pest status during near future (NF) and distant future (DF) under different climate change scenarios
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