Oscillation, synchrony, and multi-factor patterns between cereal aphids and parasitoid populations in southern Brazil

Abstract

In different parts of the world, aphid populations and their natural enemies are influenced by landscapes and climate. In the Neotropical region, few long-term studies have been conducted, maintaining a gap for comprehension of the effect of meteorological variables on aphid population patterns and their parasitoids in field conditions. This study describes the general patterns of oscillation in cereal winged aphids and their parasitoids, selecting meteorological variables and evaluating their effects on these insects. Aphids exhibit two annual peaks, one in summer–fall transition and the other in winter-spring transition. For parasitoids, the highest annual peak takes place during winter and a second peak occurs in winter–spring transition. Temperature was the principal meteorological regulator of population fluctuation in winged aphids and parasitoids during the year. The favorable temperature range is not the same for aphids and parasitoids. For aphids, temperature increase resulted in population growth, with maximum positive effect at 25°C. Temperature also positively influenced parasitoid populations, but the growth was asymptotic around 20°C. Although rainfall showed no regulatory function on aphid seasonality, it influenced the final number of insects over the year. The response of aphids and parasitoids to temperature has implications for trophic compatibility and regulation of their populations. Such functions should be taken into account in predictive models.

Aphid‐parasitoids trophic relationship in a cereal crop succession system: Population oscillation and food webs

“…From December to March, the average temperatures in the region of this study are above 20°C, with average maximums above 25°C, which can be a limiting factor for the species. Engel et al (2022) punctuated a tipping point from which temperatures become unfavourable for parasitoids around 20°C, with analyzes being largely determined by A. platensis (Santos et al, 2019; Engel et al, 2022). Another intrinsic factor to be considered is the availability of host aphids that support the parasitoid populations.…”

“…Moericke traps are located in Coxilha (10 km away from Passo Fundo field Bioassay). Sampling methods and identification procedures of data on Trapsystem are described at Santos et al (2019) and Engel et al (2022).…”

“…A generalized additive model (GAM) and a generalized linear model (GLM) were used to establish the relationship between parasitism percentage sampled with exposed aphid hosts in Passo Fundo and the total density of parasitoids caught by Moericke traps in Coxilha. First, a GAM model was implemented to adjust the data on parasitism and parasite abundance captured as a function of time, as used by Engel et al (2022). For parasitism data, a quasibinomial distribution was used.…”

“…First, the most important aphid on wheat in this region was Schizaphis graminum (Rondani), but from the 1960s and 1970s onwards, with the expansion of the wheat area, Sitobion avenae (Fabricius) and, above all, Metopolophium dirhodum (Walker), reached a prominent role (Lau et al, 2021). Currently, cereal aphids occur in all Brazilian regions that produce winter cereals and in northern Rio Grande do Sul State (RS), the four main species that have winter cereals as hosts are Rhopalosiphum padi (Linnaeus), S. graminum , M. dirhodum , and S. avenae (Rebonatto et al, 2015; Engel et al, 2022; Lau et al, 2021).…”

“…In particular, the populations of M. dirhodum have reduced. In the other direction, some aphid species, like R. padi , have increased their population density (Rebonatto et al, 2015; Engel et al, 2022; Lau et al, 2021). In addition to the BCPWA, changes have occurred in the farming systems in southern Brazil since the 1980s.…”