EFFECTS OF TEMPERATURE ON ACYRTHOSIPHON PISUM AND THERIOAPHIS TRIFOLII (HEMIPTERA: APHIDIDAE) ABUNDANCE IN ALFALFA CROPS: A CASE STUDY IN NORTHERN SERBIA

Populations of the most abundant alfalfa aphids, Acyrthosiphon pisum and Therioaphis trifolii, have periodic fluctuations, and many factors affect their dynamics. In the present study, we examined the impact of daily air temperatures on the abundance of two alfalfa aphids in field conditions. The numbers of these two aphids on alfalfa were documented at two locations in a representative alfalfa growing area in Serbia during a three-year field study. Based on the records of aphid abundance and daily air temperatures during the whole study, it was found that a correlation between the sum of optimal daily air temperatures for aphid development, the sum of maximum daily air temperatures and the number of recorded aphid peaks was significant and can therefore be considered for the detection of suitable temperature conditions to increase aphid abundance. The study shows that the highest correlations were between a high density of A. pisum and the sum of optimal daily air temperatures for its development (Ck=0.569) and between a high density of T. trifolii and the sum of maximum daily air temperatures (Ck=0.595). The length of time required for the growth of populations of the two alfalfa aphids differed: 30 days for A. pisum and 5 days for T. trifolii. The association of temperature data to alfalfa aphid abundance enables a projection of their population behavior in changed future climate conditions. This study suggests increased population sizes of T. trifolii and decreased population sizes of A. pisum on alfalfa under the warmer conditions that are expected to prevail in the future. © 2022 Journal of Agricultural Sciences (Belgrade). All rights reserved

Landscape composition and configuration influence cereal aphid-parasitoid-hyperparasitoid interactions and biological control differentially across years

The loss of landscape heterogeneity through agricultural intensification is known to affect aphid-parasitoid-hyperparasitoid interactions, with consequences for biological control. Various aspects of landscape heterogeneity (e.g. landscape composition and configuration) are expected to affect these interactions differentially, but there were few attempts to empirically compare the influence of separate landscape features on pest-parasitoid dynamics. To address these questions, we conducted three simultaneous studies in wheat fields in northern Serbia, to compare the effects of contrasting landscape contexts: (1) simple vs. more complex landscapes; (2) large- vs. small-field landscapes; (3) large-field areas with contrasting character of their marginal vegetation. We (1) found that aphid densities, parasitism rates and species richness of parasitoids and hyperparasitoids were higher in landscapes with more extensive and diversified non-crop habitats, positively affecting the biological control. We (2) did not find significant differences in aphid abundance and parasitism between large- and small-field landscapes, but we detected some contradictory patterns in aphid growth and parasitism increase; we relate both findings to certain region-specific landscape features of wider relevance. The character of marginal vegetation (3) had mixed effects on aphid-parasitoid interactions and dynamics, with respect to source of colonization. Parasitism rates above 22-24% were associated with population decline in the aphids, consistently across analyzed landscape contrasts. Other relationships were subject to significant inter-annual variability (over 2-4 years period), suggesting that effectiveness of landscape management for conservation biological control would also fluctuate year by year. Our findings show that a well-founded landscape-scale management for biological pest control in agriculture must be adjusted for differential aspects of landscape heterogeneity effects on pest-parasitoid interactions