Population dynamics and natural mortality factors of the Oriental armyworm, Mythimna separata (Lepidoptera: Noctuidae), in South-Central India

Abstract

The population dynamics and key mortality factors of the Oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae), a serious pest of cereal crops in Asia and Australia, were studied in southern India. Adults were generally caught in light traps 15-20 days after the initiation of the monsoon rains in the first week of June, and reached a peak in September, nearly one month after the peak in larval density. Rainfall, and maximum and minimum relative humidity were positively associated moth catches in the light traps, while maximum temperature, open pan evaporation, solar radiation, sunshine hours, and wind velocity showed a negative correlation with moth abundance. Stepwise regression analysis of moth catches with weather conditions over the previous 2 and 4 weeks explained 54-68% of the variation in the number of moths caught in the light traps. Five hymenopteran parasitoids [Costesia ruficrus (Haliday), Metopius rufus Cameron, Disophyrys sp., Compoletis chlorideae Uchida, Enicospilus sp.], and five dipteran parasitoids [Carcelia illota (Curran), Sturmiopsis inferens Townsend, Palexorista solennis (Walker), P. laxa (Curran), and Megasellia sp.], mermithid (Neoplectana sp.), and nuclear polyhedrosis virus (NPV) regulated its populations under natural conditions. Parasitism levels were much greater in sorghum (34.6%) than in pearl millet (17.6%). Cotesia ruficrus was the principle mortality factor, which caused up to 47% parasitism in October. Its activity was greater in sorghum (24.6%) than in pearl millet (14.9%). This parasitoid species could be exploited for the biological control of this pest.

Interaction of the fluctuation of the population density of sweet potato pests with changes in farming practices, climate and physical environments: A 11-year preliminary observation from South-Kivu Province, Eastern DRCongo

“…Climate change may change insect pest patterns. Hence, climate change may affect insect fitness and distribution in a given agroecological zone (Hance et al 2007;Jackson et al 2003;Okonya and Kroschel 2013ab;Parr et al 2014;Sharma et al 2002). Also, climate change (rising temperatures) may allow shifts in home range such as facilitating establishment of the pest in higher/lower altitudes where it was not found before.…”

“…Much as relationships between climatic factors and pest population density are complex, abundant rainfall (rise/decrease in temperature) may create ideal conditions for the survival of the pest and this in turn, impacts the level of damage and pressures on the crop stage concerned (Hance et al 2007;Jackson et al 2003;Okonya and Kroschel 2013ab;Parr et al 2014;Sharma et al 2002) Relatively higher rainfall figures may suggest an abundance of food and pest breeding sites (ideal conditions for rapid multiplication of the pest population) all month-year round. The creation of ideal conditions for rapid build-up of the populations (various generations) is likely to impact on the change in the prevalence status of the pests and hence on health status of the crop that is now being submitted to high pressure of the pest and therefore high damage, which is likely to impact on the yield.…”

Impact of climate change on insect pests, plant chemical ecology, tritrophic interactions and food production

“…Oriental armyworm (Mythimna separate Walker) populations increase when extended periods of drought (which is detrimental to the natural enemies) are followed by heavy rainfall [54]. Changes in interspecific interactions could also alter the effectiveness of natural enemies [7,8].…”

Biological Consequences of Climate Change on Arthropod Biodiversity and Pest Management

“…O rie n tal arm yw orm , M ythim na separata (Walk.) populations increase during extended periods of drought (w hich is d etrim en tal to th e natural enem ies), followed by heavy rainfall (Sharma et al 2002). Aphid abundance increases with an increase in C 0 2 and temperature, however, the parasitism rates remain unchanged in elevated C 0 2 Temperature not only affects the rate of insect development, but also has a profound effect on fecundity and sex ratio of parasitoids (Dhillon and Sharma 2009).…”