Seasonal abundance of aphid species on lettuce crops in Central Spain and identification of their main parasitoids

Abstract

The objective of this work was to determine the population dynamics of aphid species associated to lettuce crops in Central Spain and to identify their main parasitoids. Three aphid species were found colonising lettuce crops: Nasonovia ribisnigri (Mosley), Macrosiphum euphorbiae (Thomas) and Aulacorthum solani (Kaltenbach). The most abundant aphid species in both spring and autumn crops was N. ribisnigri, with a population peak on 29 May (80 individuals per plant) for the spring crop and on 25 October (50 individuals per plant) for the autumn crop in 2001. In 2002, population peaks of N. ribisnigri occurred on 9 May (132 individuals per plant) and on 6 November (18 individuals per plant). In spring M. euphorbiae was also present at its beginning (late April) while A. solani was the second most abundant species in autumn. To develop a simplified presence/absence sampling procedure, the data obtained on the mean number of N. ribisnigri per plant present during the whole study was regressed to the percentage of plants infested with one or more and five or more aphids.

N. ribisnigri colonies on lettuce were found to be parasitized by various braconid wasp species: Aphidius hieraciorum Starý, Aphidius ervi Haliday, and Aphidius colemani Viereck. This is the first report of A. hieraciorum acting as a parasitoid of N. ribisnigri in Spain. Parasitoids were also sampled in natural vegetation located within or adjacent to lettuce crops. The following host/parasitoid combinations were found on natural flora close or within lettuce fields: Hyperomyzus lactucae (L.) parasitized by Aphidius sonchi Marshall and Praon volucre (Haliday); Brachycaudus helichrysi Kaltenbach, by Diaeretiella rapae (M’Intosh); Aphis fabae Scopoli by Lysiphlebus testaceipes (Cresson) and Uroleucon sonchi (L.) by Aphidius funebris Mackauer. The role of natural vegetation as a possible reservoir and source of parasitoids regulating the population of aphids found on nearby lettuce crops is discussed.