Limitations of allometry, morphometry, and fluctuating asymmetry in detecting environmental stress caused by lead soil contamination in aphids under field conditions

ABSTRACT One of the tools used to investigate the influence of environmental contaminants and other stresses on the development of organisms is the analysis of morphometric traits used to detect changes in growth and size patterns. To evaluate the effects of the heavy metal lead (Pb) present in experimentally contaminated soil on the morphometric traits of the aphid Brevicoryne brassicae (L.) reared on cultivated Brassica oleracea L. (var. acephala), we analyzed three different metrics: morphometry, allometry, and fluctuating asymmetry (FA). Additionally, we aimed to assess the effectiveness of these analyses in detecting environmental stress. We cultivated kale plants in soil contaminated with the maximum allowable limit of Pb for local soils in Brazil, and the colonization of plants by aphids occurred naturally under field conditions. After collection, we photographed and measured the antennae, tibiae, and total body length of aphids from the control and contaminated treatments. We observed no significant differences in the allometry and morphometric analysis, and the presence of the contaminant did not result in any observed FA. The study demonstrated that the morphometric trait analyses employed were not effective in detecting environmental stress resulting from field exposure of aphids to Pb in soil, since these insects suffered a reduction in their population density in the presence of Pb, as indicated in our previous findings. This result diverges from those found in studies conducted under laboratory conditions. We discussed mechanisms of metal accumulation, detoxification in aphids, and population aspects in natural conditions.

A new interaction in an invasive plant in Brazil: Horismenus abnormicaulis (Hymenoptera, Eulophidae) parasitizing Acanthoscelides macrophthalmus (Coleoptera, Chrysomelidae, Bruchinae) in seeds pods of Leucaena leucocephala (Fabaceae)

ABSTRACT The parasitism of Acanthoscelides macrophthalmus (Coleoptera, Chrysomelidae, Bruchinae) by the parasitoid Horismenus abnormicaulis (Hymenoptera: Eulophidae) is described for the first time. We harvested 90 Leucaena leucocephala (Fabaceae, Mimosoideae) fruit pods, in June 2019 on the campus of the Federal University of Lavras in the municipality of Lavras, Minas Gerais, Brazil. We found 21 individuals of H. abnormicaulis and 334 of A. macrophthalmus. The presence of cephalic capsule of beetle's pupa and evidence of predation into seed pods from which the wasps emerged suggested H. abnormicaulis is a parasitoid of A. macrophthalmus. Horismenus abnormicaulis has been added to the list of A. macrophthalmus parasitoids, and its occurrence has been expanded to the state of Minas Gerais. This discovery expands our knowledge of H. abnormicaulis biology and distribution in Brazil, as well as the tri-trophic interaction, plant-herbivore-parasitoid in invasive plant systems.