Comparing floral resource maps and land cover maps to predict predators and aphid suppression on field bean

Context Predatory insects contribute to the natural control of agricultural pests, but also use plant pollen or nectar as supplementary food resources. Resource maps have been proposed as an alternative to land cover maps for prediction of beneficial insects. Objectives We aimed at predicting the abundance of crop pest predating insects and the pest control service they provide with both, detailed flower resource maps and land cover maps. Methods We selected 19 landscapes of 500 m radius and mapped them with both approaches. In the centres of the landscapes, aphid predators – hoverflies (Diptera: Syrphidae), ladybeetles (Coleoptera: Coccinellidae) and lacewings (Neuroptera: Chrysopidae) – were surveyed in experimentally established faba bean phytometers (Vicia faba L. Var. Sutton Dwarf) and their control of introduced black bean aphids (Aphis fabae Scop.) was recorded. Results Landscapes with higher proportions of forest edge as derived from land cover maps supported higher abundance of aphid predators, and high densities of aphid predators reduced aphid infestation on faba bean. Floral resource maps did not significantly predict predator abundance or aphid control services. Conclusions Land cover maps allowed to relate landscape composition with predator abundance, showing positive effects of forest edges. Floral resource maps may have failed to better predict predators because other resources such as overwintering sites or alternative prey potentially play a more important role than floral resources. More research is needed to further improve our understanding of resource requirements beyond floral resource estimations and our understanding of their role for aphid predators at the landscape scale.

Intraguild Predation between Chrysoperla carnea (Neuroptera: Chrysopidae) and Hippodamia variegata (Coleoptera: Coccinellidae) at Various Extraguild Prey Densities and Arena Complexities

Intraguild predation (IGP) is a ubiquitous, important and common interaction that occurs in aphidophagous guilds. The effects of extraguild prey (EGP, i.e., aphids) density, predator life stage combinations and duration of the interaction on the level, asymmetry and direction of intraguild predation between lacewing Chrysoperla carnea and ladybird Hippodamia variegata were examined in simple laboratory arena and more complex microcosm environment. Three initial densities of 50, 150 and 400 Aphis fabae third instar nymphs and a control without aphids were provided to six combinations of predator life stages (2nd and 3rd larval instars of lacewing and 3rd and 4th instars and adult females of ladybird). The remaining aphid density and occurrence of IGP were checked after 24, 48 and 72 h. The IGP intensity (IGP level, IL) was similar in the simple arena (reaching 0.6 between larvae in absence of EGP and 0.3 between lacewing larvae and ladybird females) and microcosm environment (0.3 without EGP). In both environments, increasing EGP density lowered IL according to negative exponential relationship. IGP was asymmetric (general average asymmetry was 0.82 in simple arena and 0.93 in microcosm, the difference was not significant) and mostly in favour of larvae of C. carnea, except in the combination of 2nd larvae of C. carnea with the 4th larvae and adults of H. variegata. The direction of IGP, but not other characteristics, partially changed during the duration of the experiment. The incidence of IGP interactions among aphid predators under real conditions and its consequences on aphid biological control are discussed.

Population abundance of pomegranate aphid, Aphis punicae (Homoptera: Aphididae), predators in Southwest of Iran

Pomegranate aphid, Aphis punicae Passarini (Hom., Aphididae) is an important pest of pomegranate in Iran. Predators play critical role in natural control of the pest. In this study, seasonal population dynamics of the aphid predators were investigated during two years (2016/2017) in Ilam province, southwest of Iran. Samplings were bi-weekly performed in an experimental pomegranate orchard. Four insect predators, Coccinella septempunctata L., Oenopia congelobata L. (Col., Coccinellidae), Xanthogramma pedisseguum Haris (Dip., Syrphidae) and Chrysoperla carnea Stephens (Neu., Chryspidae) were identified as predators of A. punicae in Ilam. The natural enemies occurred during March to May in both years. The highest and the lowest densities were belong to X. pedisseguum and O. congelobata, respectively. Results of the study can be used for developing integrated pest management program of A. punicae in pomegranate orchards.