First Analyses of Lysine Succinylation Proteome and Overlap between Succinylation and Acetylation in Solenopsis Invicta Buren (Hymenoptera: Formicidae)

Background: Lysine succinylation (Ksu) exists in both eukaryotes and prokaryotes, and influences a variety of metabolism processes. However, little attention has been paid to Ksu in insects, especially the notorious invasive pest Solenopsis invicta. Results: In this study, the first analyses of Ksu proteome and overlap between Ksu and lysine acetylation (Kac) in S. invicta were presented. 3,753 succinylated sites in 893 succinylated proteins were tested. The dihydrolipoyl dehydrogenase, V-type proton ATPase subunit G, and tubulin alpha chain all had evolutionary conservatism among diverse ant or bee species. Immunoblotting validation showed that there were many Ksu protein bands with a wide range of molecular mass. In addition, 1,230 sites in 439 proteins were highly overlapped between Ksu and Kac. 54.05% of Ksu proteins in cytoplasm were acetylated. The results demonstrated that Ksu may play a vital part in the allergization, redox metabolism, sugar, fat, and protein metabolism, energy production, immune response, and biosynthesis of various secondary metabolites.Conclusions: Ksu and Kac were two ubiquitous protein post-translational modifications participated in a variety of biological processes. Our results may supply rich resources and a starting point for the molecular basic research of regulation on metabolic pathways and other biological processes by succinylation and acetylation.

Susceptibility of Boll Weevil (Coleoptera: Curculionidae) to Ethiprole, Differential Toxicity Against Selected Natural Enemies, and Diagnostic Concentrations for Resistance Monitoring

Synthetic insecticide application is one tactic for reducing boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), infestations during the cotton, Gossypium hirsutum L., reproductive stage. We assessed the susceptibility of the boll weevil and its natural enemies to ethiprole (mode of action 2B), a phenylpyrazole insecticide, and diagnostic concentrations of ethiprole indicative of boll weevil susceptibility. Differences in the lethal concentrations of ethiprole were calculated with susceptibility ratios based on LC50 ranging from 2.89- to 10.34-fold relative to a natural susceptible population. The lowest and the highest recommended field rates of ethiprole, 100 and 200 g a.i./ha, produced residues that caused 83.3% and 93.7% mortality of weevils caged with cotton leaves from field-treated plants for 8 d. We found that ethiprole was less toxic than fipronil to the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) and to the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), while fipronil was highly toxic to both. Adult earwigs, Euborellia annulipes Lucas (Dermaptera: Anisolabididae), were relatively tolerant to ethiprole and fipronil at the highest field rates. Pooled LC50-and LC95-concentrations of ethiprole calculated from studied populations were used as diagnostic for boll weevil mortality, and the outcome fitted to the expected mortality for boll weevil populations from different locations serving for further control failure assessment. Ethiprole appears to be suitable for boll weevil control with low impact on natural enemy communities.

Silencing of CYP6AS160 in Solenopsis invicta Buren by RNA interference enhances worker susceptibility to fipronil

Cytochrome P450 monooxygenases play a key role in pest resistance to insecticides by detoxification. Four new P450 genes, CYP6AS160, CYP6AS161, CYP4AB73 and CYP4G232 were identified from Solenopsis invicta. CYP6AS160 was highly expressed in the abdomen and its expression could be induced significantly with exposure to fipronil, whereas CYP4AB73 was not highly expressed in the abdomen and its expression could not be significantly induced following exposure to fipronil. Expression levels of CYP6AS160 and CYP4AB73 in workers were significantly higher than that in queens. RNA interference-mediated gene silencing by feeding on double-stranded RNA (dsRNA) found that the levels of this transcript decreased (by maximum to 64.6%) when they fed on CYP6AS160-specific dsRNA. Workers fed dsCYP6AS160 had significantly higher mortality after 24 h of exposure to fipronil compared to controls. Workers fed dsCYP6AS160 had reduced total P450 activity of microsomal preparations toward model substrates p-nitroanisole. However, the knockdown of a non-overexpressed P450 gene, CYP4AB73 did not lead to an increase of mortality or a decrease of total P450 activity. The knockdown effects of CYP6AS160 on worker susceptibility to fipronil, combined with our other findings, indicate that CYP6AS160 is responsible for detoxification of fipronil. Feeding insects dsRNA may be a general strategy to trigger RNA interference and may find applications in entomological research and in the control of insect pests in the field.

Establishment and Social Impacts of the Red Imported Fire Ant, Solenopsis invicta, (Hymenoptera: Formicidae) in Taiwan

The first report of the red imported fire ant (RIFA), Solenopsis invicta Buren, in Taiwan was in the city of Taoyuan in 2003. The government has made great efforts to bring RIFA-infested areas under control. RIFA has gradually spread outward since its discovery, but it is still confined in northern Taiwan, in part due to the control efforts. RIFA is well established in densely populated environments (i.e., urban areas), causing damage to public utilities and significantly affects the inhabitants of Taiwan. Out of 10,127 human encounters with RIFA reported by the Plant Pest Information Management System in the Bureau of Animal and Plant Health Inspection and Quarantine, Council of Agriculture, Executive Yuan, 3819 (37.71%) persons were stung, with 834 (21.8%) persons exhibiting wheal-and-flare reaction (swelling and redness of the skin). Among the victims, 288 (7.5%) sought medical care, and about 21 (0.6%) developed severe cellulitis and urticaria. Unexpectedly, 2.8% (106) of the victims exhibited anaphylactic shock, which was higher than previously reported cases (1%). The high anaphylactic shock percentage was probably because most victims were elderly farmers or because Asian people have higher sensitivity to the RIFA sting. RIFA is well adapted to the environmental conditions in Taiwan, which makes it extremely difficult (if not impossible) to eradicate. The management of RIFA in the future should focus on lowering the speed of spread to mitigate possible dangers to the inhabitants. Six major challenges of RIFA management in Taiwan are also discussed.