Season and weather affect the mortality of immature stages of Ascia monusteorseis (Lepidoptera: Pieridae) caused by natural factors

Abstract

In this study, we evaluated the causes of mortality in immature stages of Ascia monuste orseis Godart 1918 (Lepidoptera: Pieridae) over each of four seasons, for 2 years, on an experimental cabbage plot using life tables. We addressed two key questions: (1) Do the mortality rates caused by a factor vary by season? And (2) how does the local weather contribute to such variation? We identified five causes of mortality (failure, pathogens, parasitism, predation and rainfall) that together tended to be higher during wet–warm conditions with values up to 94%. However, each cause and its mortality rate varied among seasons. Failure was observed in all stages and tended to increase during cold conditions with a negative relationship with air temperature and relative humidity and positive for precipitation. Larval and pupal predation increased during warm conditions and was positively associated with both air temperature and relative humidity. Conversely, in seasons with intense precipitation, pupal predation was reduced and had a negative relationship. Rainfall caused mortality of eggs and larvae, mostly during intense events, and egg mortality also showed a positive and significant association with precipitation. Larval parasitism was low, and pathogens were noted in larvae and pupae, but we did not find variation by season for these factors. Our results indicate that mortality caused by failure, predation and rainfall on immature stages of A. monuste orseis can vary among seasons and appear to be related to local weather. These findings improve our comprehension of how local weather affects the immature stages of a neotropical pest and the associated mortality factors.

Weathering the hunt: The role of barometric pressure in predator insects' foraging behaviour

“…Interestingly, after rainfall, the populations of pest crop insects tend to increase due to the limitation of natural enemy activity (Catling & Islam, 1995 ; Weisser et al, 1997 ). Rain is a significant mortality factor that affects not only prey availability but also impacts foraging behaviour (Kasper et al, 2008 ; Santos et al, 2020 ). As a result, when confronted with low‐pressure conditions, which are associated with strong winds and rain, predators might reduce their foraging efforts, resulting in lower consumption rates.…”

Do patterns of insect mortality in temperate and tropical zones have broader implications for insect ecology and pest management?

“…Abiotic factors such as temperature and rainfall are well-known causes of insect mortality ( Birch, 1957 ; Krebs, 2014 ; Varella et al, 2015 ; Santos et al, 2020 ). However, because the MDLT analysis had actual measurements of mortality by cause, our results suggest that both temperate and tropical insects experience large mortality from abiotic factors, when considering both mortality in the presence of other factors and irreplaceable mortality.…”

Assessing the temporal dynamics of Frankliniella schultzei (Thysanoptera: Thripidae) in commercial soybean crops in North Brazil

“…Our best model describing the relationship between F. schultzei density and the explanatory variables (predators and weather) included photoperiod and rainfall only, with absolute counts negatively affected by the latter. The rainfall effect on pest population size is expected to play a significant role in tropical areas due to slight temperature variations and dry/wet seasons well defined (Alvares et al ., 2013; Santos et al ., 2020). For instance, infestations of C. phaseolis on bean crops in Brazil are not affected by either temperature or relative humidity, while rainfall contributes to a slight reduction in the population density (Boiça‐Júnior et al ., 2015).…”

“…For instance, infestations of C. phaseolis on bean crops in Brazil are not affected by either temperature or relative humidity, while rainfall contributes to a slight reduction in the population density (Boiça‐Júnior et al ., 2015). An important aspect is that rains, among other factors, depend on their intensity, with heavy events contributing to higher mortality rates (Santos et al ., 2020). The mechanical impact of raindrops on small insects (such as thrips) can kill them, knock them to the ground or drown them, causing a marked reduction in their population density (Nyasani et al ., 2013).…”