Olfactory behavior and response of household ants (Hymenoptera) to different types of coffee odor: A coffee-based bait development prospect

Acute exposure to caffeine improves foraging in an invasive ant

Argentine ants, Linepithema humile, are a particularly concerning invasive species. Control efforts often fall short likely due to a lack of sustained bait consumption. Using neuroactives, such as caffeine, to improve ant learning and navigation could increase recruitment and consumption of toxic baits. Here, we exposed L. humile to a range of caffeine concentrations and a complex ecologically relevant task: an open landscape foraging experiment. Without caffeine, we found no effect of consecutive foraging visits on the time the ants take to reach a reward, suggesting a failure to learn the reward's location. However, under low to intermediate caffeine concentrations ants were 38% faster with each consecutive visit, implying that caffeine boosts learning. Interestingly, such improvements were lost at high doses. In contrast, caffeine had no impact on the ants' homing behavior. Adding moderate levels of caffeine to baits could improve ant's ability to learn its location, improving bait efficacy.

Invasive ant learning is not affected by seven potential neuroactive chemicals

Argentine ants Linepithema humile are one of the most damaging invasive alien species worldwide. Enhancing or disrupting cognitive abilities, such as learning, has the potential to improve management efforts, for example by increasing preference for a bait, or improving ants' ability to learn its characteristics or location. Nectar-feeding insects are often the victims of psychoactive manipulation, with plants lacing their nectar with secondary metabolites such as alkaloids and non-protein amino acids which often alter learning, foraging, or recruitment. However, the effect of neuroactive chemicals has seldomly been explored in ants. Here, we test the effects of seven potential neuroactive chemicals-two alkaloids: caffeine and nicotine; two biogenic amines: dopamine and octopamine, and three nonprotein amino acids: β-alanine, GABA and taurine-on the cognitive abilities of invasive L. humile using bifurcation mazes. Our results confirm that these ants are strong associative learners, requiring as little as one experience to develop an association. However, we show no short-term effect of any of the chemicals tested on spatial learning, and in addition no effect of caffeine on short-term olfactory learning. This lack of effect is surprising, given the extensive reports of the tested chemicals affecting learning and foraging in bees. This mismatch could be due to the heavy bias towards bees in the literature, a positive result publication bias, or differences in methodology.

Development and Characterization of Novel Polymorphic Microsatellite Markers for Tapinoma indicum (Hymenoptera: Formicidae)

Tapinoma indicum (Forel) (Hymenoptera: Formicidae) is a nuisance pest in Asia countries. However, studies on T. indicum are limited, especially in the field of molecular biology, to investigate the species characteristic at the molecular level. This paper aims to provide valuable genetic markers as tools with which to study the T. indicum population. In this study, a total of 143,998 microsatellite markers were developed based on the 2.61 × 106 microsatellites isolated from T. indicum genomic DNA sequences. Fifty selected microsatellite markers were amplified with varying numbers of alleles ranging from 0 to 19. Seven out of fifty microsatellite markers were characterized for polymorphism with the Hardy-Weinberg equilibrium (HWE) and linkage disequilibrium (LD) analysis. All seven microsatellite markers demonstrated a high polymorphic information content (PIC) value ranging from 0.87 to 0.93, with a mean value of 0.90. There is no evidence of scoring errors caused by stutter peaks, no large allele dropout, and no linkage disequilibrium among the seven loci; although loci Ti-Tr04, Ti-Tr09, Ti-Te04, Ti-Te13, and Ti-Pe5 showed signs of null alleles and deviation from the HWE due to excessive homozygosity. In conclusion, a significant amount of microsatellite markers was developed from the data set of next-generation sequencing, and seven of microsatellite markers were validated as informative genetic markers that can be utilized to study the T. indicum population.

Variant Ionotropic Receptors are Expressed in the Antennae of Anopheles sinensis (Diptera: Culicidae)

Mosquitoes transmit many harmful diseases that seriously threaten public health. The mosquito's olfactory system is of great significance for host selection. Inotropic receptors (IRs) and olfactory receptors (ORs) have been demonstrated to be capable of odorant molecular recognition. Analyzing the molecular principles of mosquito olfaction facilitates the development of prevention and therapy techniques. Advances in the understanding of IRs have been seriously inadequate compared to those of ORs. Here, we provide evidence that 35 Anopheles sinensis IR (AsIR) genes are expressed, 7 of which are in the antennae and 2 have expression levels that are upregulated with a blood meal. A homologous analysis of the sequences showed that AsIRs are a subfamily of ionotropic glutamate receptors (iGLURs). This is the first that time IRs have been identified in Anopheles sinensis in vitro. The ultrastructure of the antennae supports the theory that diverse sensilla are distributed in the antennae. The results here may facilitate the revelation of the regulation mechanism in AsIRs, which could mitigate the transmission of diseases by mosquitoes.