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

Abstract

1. In the 1970s, cereal aphids populations (specially Metopolophium dirhodum) were out of balance in the subtropical region of South America and a successful biological control program with the introduction of parasitoids restored equilibrium. After that, changes in crop systems may have affected aphid-parasitoid communities.2. The objective of this work was to evaluate the current assemblage of cereal aphid parasitoids, describing their oscillations, parasitism level, and trophic relationships in food webs in a cereal succession system (wheat-corn-oat) currently adopted in this region.3. Over a year, the associated parasitoid/hyperparasitoid species were inventoried by field-exposed Rhopalosiphum padi, Schizaphis graminum, M. dirhodum, and Sitobion avenae (recruitment method) and by Moericke traps. 4. Six species of primary parasitoids were sampled in both aphids and traps with the same abundance sequence: A. platensis, A. rhopalosiphi, L. testaceipes, D. rapae, A. uzbekistanicus, and A. ervi.5. Parasitism and complexity of food webs were higher during the wheat season (winter-spring), decreasing in corn (summer) and increasing again in oat (autumn).6. In the current assemblage of cereal aphid parasitoids in the subtropical region of South America, three species of parasitoids that were already present before the biological control program and three that were introduced oscillate in abundance throughout the year, resulting in an alternation of the complexity of the food webs and in the levels of parasitism in the crop seasons. A. platensis and A. rhopalosiphi are the most abundant species and A. rhopalosiphi remains fundamental in the control of M. dirhodum and S. avenae.

Cereal Aphid Parasitoids in Europe (Hymenoptera: Braconidae: Aphidiinae): Taxonomy, Biodiversity, and Ecology

“…Several papers have considered the separation and characterization of both species [9,59,60,62], but due to their overlapping morphological characters, there is a list of synonyms of these species [9,56]. Summarizing all previous research efforts on the taxonomy A. rhopalosiphi and A. uzbekistanicus, the two species can be distinguished on the basis of the following characteristics: A. uzbekistanicus has a broad triangular forewing pterostigma, a narrow yellow ring at the base of flagellomere I, and usually fewer antennal segments (15)(16); while A. rhopalosiphi has a more elongated pterostigma, a variable color pattern of flagellomere 1 and 2 (with predominantly yellow parts of flagellomere 1 and occasionally flagellomere 2), and usually 16-17 segmented antennae [60]. Aphidius matricariae Haliday represents an additional species with a costulate petiole and an elongated pterostigma, but it is clearly characterized by three-segmented maxillary palps and two-segmented labial palps, while those of A. rhopalosiphi and A. uzbekistanicus are four-and three-segmented, respectively [63,64].…”

“…It is well known that aphids are one of the most important limiting factors of cereal production, through direct damage or by transmitting viral pathogens (e.g., barley yellow dwarf virus, wheat dwarf virus) [2][3][4][5][6][7]. Aphid parasitoids are diverse and effective natural enemies of cereal aphids [8][9][10][11][12][13][14][15][16]. It should be noted that the high importance of aphidiines as natural enemies of cereal aphids led to their introduction into North and South America [17][18][19] and Australia [20,21] to control cereal aphids.…”