Transcriptome and metabolome comprehensive analysis reveal the molecular basis of slow-action and non-repellency of cycloxaprid against an eusocial pest, Solenopsis invicta.

The eusocial pest, red imported fire ant (Solenopsis invicta), is a highly invasive species that poses significant threats to public safety, agriculture, and the ecological environment. Cycloxaprid, a newly identified effective, slow-acting, and non-repellent insecticide against S. invicta, allows contaminated individuals to transfer the insecticide among nestmates through body contact. However, the molecular-level changes occurring in S. invicta post cycloxaprid exposure and any molecular alterations contributing to the slow demise or decreased sensitivity remain unclear. In this study, transcriptomic and metabolomic techniques were used to investigate the molecular mechanisms of S. invicta exposed to cycloxaprid. Differential analysis results revealed 275, 323, and 536 differentially expressed genes at 12, 24, and 48 h, respectively. Genes involved in lipid and energy metabolism, DNA integration, and hormone synthesis were largely upregulated at 12 h, suggesting S. invicta might actively resist cycloxaprid impacts, and predominantly downregulated at 48 h, indicating further functional impairment and impending death. Also, we observed an imbalance in olfactory perception pathways at 12 h, which may indicate a disruption in the olfactory system of S. invicta. Metabolomic results showed that the regulation of most differential metabolites (DMs) was consistent with the expression changes of their related DEGs at different time points. Our study provides insights into the mechanism underlying slow-acting and non-repellent properties of cycloxaprid against S. invicta.

Phylotranscriptomics and evolution of key genes for terpene biosynthesis in Pinaceae.

Pinaceae is the largest family of conifers, dominating forest ecosystems and serving as the backbone of northern, temperate and mountain forests. The terpenoid metabolism of conifers is responsive to pests, diseases, and environmental stress. Determining the phylogeny and evolution of terpene synthase genes in Pinaceae may shed light on early adaptive evolution. We used different inference methods and datasets to reconstruct the Pinaceae phylogeny based on our assembled transcriptomes. We identified the final species tree of Pinaceae by comparing and summarizing different phylogenetic trees. The genes encoding terpene synthase (TPS) and cytochrome P450 proteins in Pinaceae showed a trend of expansion compared with those in Cycas. Gene family analysis revealed that the number of TPS genes decreased while the number of P450 genes increased in loblolly pine. Expression profiles showed that TPSs and P450s were mainly expressed in leaf buds and needles, which may be the result of long-term evolution to protect these two vulnerable tissues. Our research provides insights into the phylogeny and evolution of terpene synthase genes in Pinaceae and offers some useful references for the investigation of terpenoids in conifers.

Trichoderma metabolites trigger aggregation behavior in Formosan subterranean termites (Coptotermes formosanus).

Our previous studies have shown that some Trichoderma fungi trigger aggregation behavior in Formosan subterranean termites, Coptotermes formosanus Shiraki. However, the mechanisms underlying the induction of termite aggregation by Trichoderma fungi remain unclear. Here, we found that the aqueous or acetone extract of Trichoderma asperellum Samuels, Lieckfeldt & Nirenberg and Trichoderma virens Pers. ex Fries isolated from the gut or cuticle of C. formosanus elicited significant termite aggregation in 2-choice tests. We then screened 9 Trichoderma metabolites (3-acetoxy-2-butanone, phenol, 3-ethoxypropionic acid, ethyl 2,4-dioxovalerate, diglycolic acid, d-valine, styrene, 3-aminopyridine, and hexyl acetoacetate) that triggered termite aggregation. Among them, phenol (1 000 µg/mL), 3-ethoxypropionic acid (10 µg/mL), ethyl 2,4-dioxovalerate (1 000 µg/mL), and diglycolic acid (1 000 µg/mL) showed the strongest activities, triggering termite aggregation throughout the 24-h period. As T. asperellum and T. virens produce different metabolites that trigger aggregation behavior in termites, the mechanisms underlying the interaction between subterranean termites and Trichoderma fungi likely vary. Future studies are needed to test whether these chemicals can attract termites and increase bait consumption.

Foraging Behaviors of Red Imported Fire Ants (Hymenoptera Formicidae) in Response to Bait Containing Different Concentrations of Fipronil, Abamectin, or Indoxacarb.

The red imported fire ant, Solenopsis invicta Buren, is a severe pest with agricultural, ecological, and medical significance. The baiting treatment is one of the main methods to control S. invicta. However, few studies have evaluated the acceptance of fire ant bait. Here, field and laboratory studies were conducted to investigate the foraging behaviors of S. invicta responding to fire ant baits containing different concentrations of active ingredients (fipronil, abamectin, or indoxacarb). Field studies showed that S. invicta transported significantly less 0.0125% fipronil bait than control bait (without toxicant) and 0.0001% fipronil bait. The number of foraging ants significantly decreased with an increase in fipronil concentration. Our previous study showed that S. invicta usually buries the food treated with repellent chemicals, and interestingly, significantly more soil particles were transported into tubes containing 0.0001% fipronil bait than tubes containing control bait or 0.0125% fipronil bait. In addition, S. invicta transported significantly less 0.0005% abamectin bait than control bait, and significantly fewer ants were found in tubes containing 0.0125% abamectin bait than control bait. However, there was no significant difference in bait transport, number of foraging ants, and weight of soil particles relocated in tubes containing different concentrations of indoxacarb bait. In addition, laboratory studies showed that S. invicta transported significantly less 0.0125% fipronil bait than control bait and bait containing abamectin (0.0025% or 0.0125%) or indoxacarb (0.0125% or 0.0625%). In addition, the transport speed for the 0.0125% fipronil bait was the slowest. These results show that specific concentrations of some active ingredients may negatively affect bait acceptance for S. invicta, and should be avoided in fire ant bait production.

Paving Behavior in Ants and Its Potential Application in Monitoring Two Urban Pest Ants, Solenopsis invicta and Tapinoma melanocephalum.

Our previous study discovered that two urban pest ants, red imported fire ants, Solenopsis invicta Buren (Formicidae: Myrmicinae), and ghost ants, Tapinoma melanocephalum (Fabricius) (Formicidae: Dolichoderinae), can pave viscose surfaces with particles to facilitate food search and transport. We hypothesize that this paving behavior can be applied to monitor S. invicta and T. melanocephalum. In the present study, 3998 adhesive tapes, each with a food source (sausage), were placed in 20 locations around Guangzhou, China (181-224 tapes per location), and their efficiency to detect S. invicta and T. melanocephalum was compared with two traditional ant-monitoring methods, baiting and pitfall trapping. Overall, S. invicta was detected by 45.6% and 46.4% of baits and adhesive tapes, respectively. In each location, the percentage of adhesive tapes detecting S. invicta and T. melanocephalum was similar when compared to baits and pitfall traps. However, significantly more non-target ant species showed up on bait and pitfall traps. Seven non-target ant species-Pheidole parva Mayr (Formicidae: Myrmicinae), Pheidole nodus Smith (Formicidae: Myrmicinae), Pheidole sinica Wu & Wang (Formicidae: Myrmicinae), Pheidole yeensis Forel (Formicidae: Myrmicinae), Carebara affinis (Jerdon) (Formicidae: Myrmicinae), Camponotus nicobarensis Mayr (Formicidae: Formicinae), and Odontoponera transversa (Smith) (Formicidae: Ponerinae)-also showed tape paving behavior, but they can be easily distinguished morphologically from S. invicta and T. melanocephalum. Our study showed that the paving behavior occurs in different subfamilies of ants (i.e., myrmicinae, dolichoderinae, formicinae, and ponerinae). In addition, paving behavior can potentially be used to develop more specific monitoring methods for S. invicta and T. melanocephalum in urban areas in southern China.