Different lethal treatments induce changes in piperidine (1,1'-(1,2-ethanediyl)bis-) in the epidermal compounds of red imported fire ants and affect corpse-removal behavior

Smartphone-based molecularly imprinted sensors for rapid detection of thiamethoxam residues and applications

In order to achieve rapid detection of thiamethoxam residues in mango, cowpea and water, this study modified the screen printed carbon electrode (SPCE) to make a specific molecular imprinting sensor (Thiamethoxam-MIP/Au/rGO/SPCE) for thiamethoxam. An integrated smartphone platform was also built for thiamethoxam residue analysis. The performance of the complete system was analyzed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The system was then applied for the rapid determination of thiamethoxam residues in water, mango and cowpea samples. The results showed that the molecular sensor showed good linearity in the range 0.5–3.0 μmol/L of thiamethoxam. The detection limit of thiamethoxam was 0.5 μmol/L. Moreover, the sensor had good reproducibility and anti-interference performance. The average recovery rates of the pesticide residues in water, mango and cowpea samples were in the range of 90–110% with relative standard deviations < 5%. The rapid detection system for thiamethoxam residue constructed in this study was simple, reliable, reproducible and had strong anti-interference. It has broad application prospects in the field detection of thiamethoxam residue, and serves as a valuable reference for the further development of rapid detection technology of pesticide residues in the field of environment and food safety.

Toxicity and Sublethal Effects of Autumn Crocus (Colchicum autumnale) Bulb Powder on Red Imported Fire Ants (Solenopsis invicta)

Autumn crocus (Colchicum autumnale L.) is a medicinal plant as it contains high concentrations of colchicine. In this study, we reported that the ground powder of autumn crocus bulb is highly toxic to invasive Solenopsis invicta Buren, commonly referred to as red imported fire ants (RIFAs). Ants fed with sugar water containing 5000 mg/L of bulb powder showed 54.67% mortality in three days compared to 45.33% mortality when fed with sugar water containing 50 mg/L of colchicine. Additionally, the effects of short-term feeding with sugar water containing 1 mg/L of colchicine and 100 mg/L of autumn crocus bulb powder were evaluated for RIFAs’ colony weight, food consumption, and aggressiveness, i.e., aggregation, grasping ability, and walking speed. After 15 days of feeding, the cumulative colony weight loss reached 44.63% and 58.73% due to the sublethal concentrations of colchicine and autumn crocus bulb powder, respectively. The consumption of sugar water and mealworm (Tenebrio molitor L.) was substantially reduced. The aggregation rates decreased 48.67% and 34.67%, grasping rates were reduced to 38.67% and 16.67%, and walking speed decreased 1.13 cm/s and 0.67 cm/s as a result of the feeding of the two sublethal concentrations of colchicine and autumn crocus bulb powder, respectively. Our results for the first time show that powder derived from autumn crocus bulbs could potentially be a botanical pesticide for controlling RIFAs, and application of such a product could be ecologically benign due to its rapid biodegradation in the environment.

Differential Behavioral Responses of Solenopsis invicta (Hymenoptera: Formicidae) Workers Toward Nestmate and Non-Nestmate Corpses

The removal of corpses (aka 'necrophoric behavior') is critical to sanitation in ant colonies. However, little is known about differences in the necrophoric responses of Solenopsis invicta workers towards corpses of nestmates and non-nestmates. We introduced corpses of S. invicta workers from either intracolony (i.e., nestmate) or intercolony (i.e., non-nestmate) origin at the entrance of artificial nests, and recorded workers' aggressive responses and necrophoric behaviors for analysis. Solenopsis invicta workers displayed distinct responses towards corpses of different origins. Specifically, resident workers were more likely to remove fresh non-nestmate corpses than nestmate corpses, but there was no difference regarding corpses that had been dead for 15 min or longer. Resident workers reacted more aggressively to, and removed more quickly, fresh non-nestmate corpses than corpses of their nestmates. On the other hand, there was no significant difference in the removal time between nestmate and non-nestmate corpses that had been dead for 15 min or longer. Resident workers always displayed stronger aggressiveness towards non-nestmate corpses than nestmate corpses, excepting to corpses that had been dead for 6 h, which elicited a response. No significant correlation between the removal times and aggressiveness levels were detected in any treatments. It remains to be tested whether this differential response is adaptive in how it influences colony fitness and competition.