Body shape and fluctuating asymmetry following different feeding sources and feeding time in a triatomine, Triatoma pallidipennis (Stål, 1892)

Changes in Fluctuating Head Asymmetry in Natural Populations of Triatoma infestans (Hemiptera, Reduviidae): How Does a Vector Control Treatment Influence the Phenotype of Nymphs and Adults?

In triatomines, the measurement of fluctuating asymmetry (FA) might help us infer the (non-lethal) effects of insecticides on morphological characters and how these changes can impact activities of utmost importance in vector management. Insects that survive chemical control present morphological alterations that impact their final development. Our work measures for the first time the changes in FA in nymphs and their comparison with the occurrence of these changes in adults before and after a chemical control. We determined the occurrence and quantified the FA of the head as an indicator of stress during development in adults and fifth instar nymphs of Triatoma infestans-one of the main vectors of Trypanosoma cruzi in the southern cone of South America-to estimate the effect of exposure to insecticide in the different stages. We measured the FA of the heads of peridomestic populations of the Rioja Llanos (Argentina), pre-treatment with insecticide (15 years without chemical treatment) and post-treatment (3-4 months after the application). Our results show lower FA values in nymphs compared with adults. Furthermore, shape FA was higher post-treatment, although with some exceptions depending on sex. According to what was observed, we conclude that the post-treatment population would have differences over the pre-treatment population (FA increases), at least for fifth instar nymphs and adult males. The results are discussed considering the stage of nymphal development where the insecticide was applied, the possible repellence caused by the insecticide, the influence of insects from neighboring habitats, seasonality, and the compensatory mechanisms of development, among others. Working with field insects allows us to understand how populations react to an insecticide application, but without leaving aside characteristics of T. infestans populations under natural conditions.

The Body of Chagas Disease Vectors

Morphometry is an effort to describe or measure the morphology of the body, or parts of it. It also provides quantitative data on the interactions of living organisms with their environment, external or internal. As a discipline, morphometrics has undergone significant developments in the last decade, making its implementation more visual and less laborious. Chagas disease vectors, often referred to by the common name of "kissing bugs", belong to the subfamily Triatominae. Due to their apparent morphological plasticity, they have been the subject of numerous morphometric studies. Most of these have been applied taking into account the particularities of this group of vectors, such as domesticity (synanthropy), food preferences, dispersal ability, insecticide resistance, as well as some taxonomic issues. This brief review over nearly three decades is organized here according to the body organs considered by the authors.

New in morphometry: Geometric morphometry of the external female genitalia of Triatominae (Hemiptera: Reduviidae)

The study of geometric morphometry has an impact on Triatominae studies. Currently, several taxonomic and systematic studies use this approach. The Triatominae subfamily comprises three fossil species and 154 extant species potentially capable of transmitting Trypanosoma cruzi, the causative agent of Chagas disease. This study aims to evaluate the external female genitalia of adult triatomines using multivariate geometric morphometric approaches, not only for validation but also for systematic inferences. Specimens belonging to the genera Panstrongylus, Psammolestes, Rhodnius, and Triatoma were evaluated, in addition to two species previously included in Triatoma: T. longipennis and T. phyllosoma. The results show that the external female genitalia have operational morphology and allow characterization of the species and the genera of the Triatominae. In addition, the multivariate technique enabled delimitation of the phylogenetic relationships of the subfamily, presenting results consistent with systematic studies. It can be concluded that the external female genitalia evaluated by geometric morphometry is a useful character for the taxonomy and systematics of Triatominae.