Margarita Rocca

Diversity of Herbivorous Communities in Blueberry Crops of Different Regions of Argentina

ABSTRACT When a crop is introduced into a new region the herbivorous insect communities are structured from the regional pool of species, and the spatio—temporal heterogeneity of the landscape and the spatial arrangement of habitat elements are essential for species diversity. The blueberry, Vaccinium corymbosum L., is a crop native to the northern hemisphere and was introduced in Argentina in the 1990s. We have analyzed the richness and diversity of insect herbivore communities in several blueberry crops located in different agricultural landscapes of Buenos Aires and Entre Ríos, in Argentina. In total, the number of families recorded throughout the study period was 31. The richness and the diversity showed significant differences among phenological stages and years, although the sites had an effect on the richness, in Buenos Aires. Aphidae was the most abundant family in all sites, followed by different families depending on the surrounding crops and their more common herbivores. The highest values of cumulative alpha diversity were in crops located in more changing landscapes. There were high values of temporal beta diversity everywhere. Spatial beta diversity was higher in Buenos Aires than in Entre Ríos, probably because the crops of the latter are located in similar landscapes. Gamma diversity was 29 families for communities of Buenos Aires and it was 15 families in Entre Ríos. The herbivorous communities in blueberry crops of Argentina are shaped by ectophagous generalist (South American and cosmopolitan) from the regional pool of species, characteristic of the landscape where the crops were introduced.

Abundance of Icerya purchasi (Hemiptera: Margarodidae) and Its Parasitoid Cryptochaetum iceryae (Diptera: Cryptochaetidae) in Argentina Blueberry Crops

ABSTRACT Icerya purchasi Maskell is a polyphagous scale pest of ornamentals and several other crops. It has two natural specialist enemies that maintain its populations at low levels: Rodolia cardinalis (Mulsant) and Cryptochaetum iceryae (Williston). I. purchasi was recently observed in blueberry crops (Vaccinium corymbosum L.) in Argentina. Seven blueberry fields located in different agricultural landscapes were sampled from July 2006 to September 2008. I. purchasi was present only in the citrus areas of Gobernador Castro, San Pedro, and Concordia. In the last locality, it was present in January 2007, and the abundance was very low. In Buenos Aires, I. purchasi was more abundant in Gobernador Castro where it was present throughout all study period. In San Pedro, it was only registered in August 2007 and March, April, and June 2008. In Gobernador Castro, where the abundance was highest, the dominant crop near blueberries is citrus. The low abundance in San Pedro and Concordia fields may be attributable to the replacement of citrus crops by nonhosts. In Concordia and San Pedro fields, no parasitized I. purchasi were found. In Gobernador Castro, the proportion of adults parasitized was 0.805 ± 0.286. When the risk of parasitism was analyzed for three density categories, there were no significant differences. R. cardinalis was present only in Gobernador Castro, and very few individuals were observed. The presence and abundance of I. purchasi in blueberry crops in Argentina seems to be linked to the structure of the landscape at the regional level, and the variable incidence of C. iceryae suggests major constraints to the scales population growth.

Sampling plans for aphids and their parasitoids in blueberry fields in Argentina

Densities of aphids (Aphis gossypii and A. spiraecola) and mummified aphids at different phenological stages of a blueberry crop were estimated for the purpose of developing sampling plans. Our data set comprised 99 samples taken during the period 2006–2008 in four fields in Buenos Aires Province, Argentina. Estimation of population density based on the proportion of sample units infested by individuals was investigated. We also calculated the minimum number of sample units to estimate the density of individuals on buds and buds + flowers using enumerative sampling. The relative precision of both methods was compared. Moreover, an enumerative sequential sampling protocol was developed. The presence–absence sampling plan gave density estimates with large variances (as measured by confidence intervals and large standard errors). The aggregation of mummies was similar on buds and buds + flowers, so the required number of sample units for density estimates was the same. Relative precision of estimates was much lower for the presence–absence sampling than the enumerative sampling, even at intermediate densities. An enumerative sequential plan would be the most appropriate and useful method in management plans for aphids and mummified aphids in blueberries.

Intra‐ and interspecific interactions between aphidophagous ladybirds: the role of prey in predator coexistence

Cannibalism (CANN) and intraguild predation (IGP) may provide energy and nutrients to individuals and eliminate potential competitors. These negative competitive interactions could also affect the coexistence of predatory species. The co‐occurrence of aphidophagous ladybird species in crops creates opportunities for CANN and IGP, especially when aphids become scarce. The Lotka–Volterra model predicts the coexistence of two species if intraspecific competition is stronger than interspecific interference interactions. Cycloneda sanguinea L. and Eriopis connexa (Germar) (both Coleoptera: Coccinellidae) coexist in sweet pepper crops in La Plata (Argentina) consuming mainly Myzus persicae (Sulzer) (Hemiptera: Aphididae). The present study used laboratory experiments to estimate levels of CANN and IGP by adults and larvae on eggs, and by adults on larvae, in both the presence and absence of prey (i.e., M. persicae), to explain the effect of prey on coexistence of these two predators. Levels of CANN by C. sanguinea and E. connexa were high in the absence of aphids, and decreased when prey was present. Intraguild predation was bidirectional and asymmetric. Adults and larvae of E. connexa were more voracious IG predators of C. sanguinea than vice versa, the former being the stronger IG predator and interference competitor. Eriopis connexa always won when larvae of the same instar were compared, whereas the larger larva always won when larvae were of different instars, regardless of species. In the presence of prey, CANN by both species decreased, but IGP by E. connexa on C. sanguinea remained high, suggesting that E. connexa could displace C. sanguinea via interspecific interference competition. Other factors potentially affecting the coexistence of C. sanguinea and E. connexa in sweet pepper crops are discussed.

Host Plant Use for Oviposition by the Insidious Flower Bug (Hemiptera: Anthocoridae)

Abstract The availability of oviposition sites for the predators of arthropod pests is crucial for the success of biological control. The resources for oviposition and offspring survival offered to the predators by crops and the surrounding natural vegetation are relevant in the context of conservation biological control.The endophytic oviposition of Orius insidiosus (Say) depends on the characteristics of the plant tissues. We thus examined, by single- and multiple-choice tests, 1) the oviposition of O. insidiosus in strawberry, analyzing the tissue characteristics of the different plant structures, and 2) the preference for oviposition among strawberry, tomato, bell pepper, eggplant, and the wild South-American poppy Bidens pilosa L. (Asterales: Asteraceae). The calyx and flower petiole received more eggs than the other structures. The thickness of the external tissues did not affect oviposition. All structures of the different plants tested offer sufficient space to house eggs, except for the leaflet lamina. Bidens pilosa was preferred by ovipositing O. insidiosus over the other plants tested.The cultivation of this plant in proximity to strawberry and other horticultural crops could constitute a promising strategy for augmenting the resources for oviposition for this predator.