Sex-specific alterations in adaptive responses of Chironomus columbiensis triggered by imidacloprid chronic and acute sublethal exposures.

The use of imidacloprid is a common pest control practice in the Neotropical region. However, the imidacloprid unintended sublethal effects on Neotropical aquatic non-target arthropods and undesirable consequences for aquatic environments remain unclear. Here, we assessed the susceptibility of Chironomus columbiensis (Diptera: Chironomidae) larvae to the neonicotinoid imidacloprid and evaluated whether sublethal exposure types would trigger sex-dependent adaptive responses (e.g., emergence, body mass, reproduction, wing morphology). We conducted a concentration-mortality curve (96 h of exposure) and established chronic and acute sublethal exposure bioassays. While chronic sublethal exposures consisted of exposing individuals during their entire larval and pupal stages, the acute sublethal exposures represented a single short duration (24 h) exposure episode during either the first or fourth larval instar. Our results revealed that chronic sublethal exposure reduced the body mass of males, while acute sublethal exposures during the first instar resulted in heavier males than those that were not exposed to imidacloprid. Chronic exposure also reduced the reproduction of males and females, while the acute sublethal exposure only affected the reproduction of individuals that were imidacloprid-exposed on their later larval instar. Chronic and acute sublethal exposures did differentially affect the wing properties of C. columbiensis males (e.g., increased size when chronically exposed and highly asymmetric wings when acutely exposed in early larval phase) and females (e.g., highly asymmetric wings when chronically and acutely exposed). Collectively, our findings demonstrated that imidacloprid can cause unintended sublethal effects on C. columbiensis, and those effects are dependent on sex, exposure type, and developmental stage.

Chironomus columbiensis (Diptera: Chironomidae) as test organism for aquatic bioassays: Mass rearing and biological traits.

Chironomidae are aquatic insects that have become a model in laboratory tests to evaluate toxic effect of different pollutants. The use of chironomids as test organisms depends on standard protocols for the rearing under laboratory conditions and expanding knowledge on its biology. We standardize a culture of C. columbiensis and analyze its life cycle under laboratory conditions. The experiments were carried out with different treatments for water, temperature, and food. As a result, a protocol was proposed for the rearing of C. columbiensis under the following conditions: semi-soft and reconstituted water, shredded paper towels as a substrate, soft aeration, temperature of 22 ± 2°C, fed with 0.3 g TetraMin® twice a week and weekly renewal of 50% of the water. Under these conditions, the duration of the life cycle was 17-31 days, with a continuous growth of 1.16 to 14.05 mm in the larval stage and an average of 530 eggs per oviposition. In comparison with other species in the family, this study indicated that C. columbiensis is a species with a short life cycle, sensible to changing conditions (e.g., temperature and food), wide distribution, so is a good organism for being used in aquatic bioassays.

Exposures to deltamethrin on immature Chironomus columbiensis drive sublethal and transgenerational effects on their reproduction and wing morphology.

Sublethal exposure to insecticides can trigger unintended responses in non-target insects that may disrupt reproductive and developmental performances of these organisms. Here, we assessed whether sublethal exposure to the pyrethroid insecticide deltamethrin in early life had sublethal and transgenerational effects on the reproduction (i.e., fecundity and fertility) and wing morphology of Chironomus columbiensis, an aquatic insect used as a water quality indicator. We first conducted concentration-response bioassays to evaluate the susceptibility of C. columbiensis larvae to deltamethrin. Our results revealed that deltamethrin toxicity was approximately 7-fold higher when C. columbiensis larvae where exposed to 96 h (LC50 = 0.17 [0.15-0.20] µg/L) than to 24 h (LC50 = 1.17 [0.97-1.43] µg/L). Furthermore, the sublethal exposures (at LC1 = 0.02 µg/L or LC10 = 0.05 µg/L) of immature C. columbiensis resulted in lower fecundity (e.g., reduced eggs production) and morphometric variation wing shapes. Further reduction in fertility rates (quantity of viable eggs) occurred at deltamethrin LC10 (0.05 µg/L). Almost 80% of the fecundity was recovered with only a single recovery generation; however, two subsequent recovery generations were not sufficient to fully recover fecundity in C. columbiensis. Specimens recovered from 98.5% of wing morphometric variation after two consecutive generations without deltamethrin exposure. Collectively, our findings demonstrates that sublethal exposure to synthetic pyrethroids such as deltamethrin detrimentally affect the reproduction and wing shape of C. columbiensis, but also indicate that proper management of these compounds (e.g., concentration and frequency of application) would suffice for these insects' population recovery.

Incidence of deformities and variation in shape of mentum and wing of Chironomus columbiensis (Diptera, Chironomidae) as tools to assess aquatic contamination.

Constantly, aquatic ecosystems are under pressure by complex mixtures of contaminants whose effects are not always easy to evaluate. Due to this, organisms are sought in which early warning signs may be detected upon the presence of potentially toxic xenobiotic substances. Thereby, the study evaluated the incidence of deformities and other morphometric variations in the mentum and wing of Chironomus columbiensis exposed to water from some of the Colombian Andes affected by mining, agriculture, and cattle raising. Populations of C. columbiensis were subjected throughout their life cycle (24 days) for two generations (F1 and F2). Five treatments were carried out in controlled laboratory conditions (water from the site without impact, site of mining mercury, mining mercury + cyanide, cattle raising, and agriculture) and the respective control (reconstituted water). Thereafter, the percentage of deformities in the mentum was calculated, and for the morphometric analysis 29 landmarks were digitized for the mentum and 12 for the wing. As a result, four types of deformities were registered in the C. columbiensis mentum, like absence of teeth, increased number of teeth, fusion and space between teeth, none of them detected in the individuals from the control. Additionally, the highest incidence of deformity in F1 occurred in the treatment of mining mercury, while for F2 this took place in the treatments of mining mercury + cyanide, cattle raising and agriculture. Differences were also found with respect to the morphometric variations of the mentum and wing of C. columbiensis among the control and the treatments with water from the creeks intervened. The treatments of mining mercury + cyanide and agriculture had the highest morphological variation in the mentum and wing of C. columbiensis. The results suggest that the anthropogenic impacts evaluated generate alterations in the oral apparatus of the larval state of C. columbiensis and in the adult state provoke alterations in the wing shape (increased width and reduced basal area). These deformities may be related to multiple stress factors, among them the xenobiotics metabolized by the organisms under conditions of environmental contamination.