Alterations in the oxidative metabolism of Rhipicephalus (Boophilus) microplus ticks in response to exposure to the insect growth regulator fluazuron

Accurate Analysis of Tricarboxylic Acid Cycle Metabolites and Anion Components in Hemocytes by IC-CD/ESI-MS for Quantifying Insecticide Impairment on Cellular Immunity in Mythimna separata

Insecticides are more broadly known to affect insect cellular immunity, but the components in hemocytes and their response to insecticide stress are still unknown. In this paper, a method based on trifluoroacetic acid extraction, followed by IC-CD/ESI-MS analysis, was developed to simultaneously determine tricarboxylic acid (TCA) cycle metabolites and anion components in hemocytes from Mythimna separata larvae. Validation gave excellent selectivity, recovery (88.7-107.6%), linear correlation (r² > 0.9961), precision (<3.89%), LOD (0.002-0.006 mg/L), LOQ (0.006-0.020 mg/L), and a short chromatographic run. The method was verified by administration of 4-((3-chloro-4-fluorophenyl)amino)-7-methoxyquinazolin-6-yl 3-(1,3-dioxoiso-indolin-2-yl) propanoate (QDP) or emamectin benzoate (EMB) to hemocytes in vitro and larvae in vivo. TCA metabolites including citrate, α-ketoglutarate, fumarate, malate, and oxaloacetate, and anions including acetate, oxalate, chloride, carbonate, and sulfate were identified and clearly separated. QDP and EMB showed a biphasic dose effect on TCA metabolites, and the contrary hormesis paralleled the different actions of QDP and EMB. The inhibition or improvement of cellular immunity depended on the QDP concentration. In conclusion, a highly sensitive, reliable, and robust method was developed, enabling the monitoring of hemocyte immunity by the quantification of TCA metabolites and anion components in minute hemocyte samples.

Activity of carboxylesterases, glutathione-S-transferase and monooxygenase on Rhipicephalus microplus exposed to fluazuron

The objective of this study was to assess the effect of the exposure to fluazuron on the activity of common pesticide detoxification enzyme groups in the cattle tick (Rhipicephalus microplus). Engorged females of a susceptible strain (POA) and a resistant strain (Jaguar) were exposed in vitro to fluazuron and their eggs and larvae were used to compare the activities of the general esterases, mixed-function oxidases (MFO) and glutathione-S-transferase (GST). The results showed significant elevation in MFO contents and esterases activity in the resistant strain when compared with the susceptible strain, in eggs and larvae respectively. In the POA strain, the MFO activity in eggs was down-regulated by fluazuron exposure. Based on these results, it can be concluded that different detoxification enzymes can act in distinct pathways depending on the tick's development stage, and may be related to fluazuron detoxification in resistant strains.