The discrepancy between fire ant recruitment to and performance on rodent carrion

Ants have not been considered important in the process of vertebrate carrion decomposition, but a recent literature review reported over 150 carrion-visiting ant species. Though many ant species have been observed to remove carrion tissue and consume carrion-exuded liquids, the significance of ant recruitment to vertebrate carrion is poorly understood. We conducted a combination of field and laboratory experiments to quantify red imported fire ant recruitment to rodent carrion and determine whether consuming rodent carrion is beneficial to ant colony performance. In the field, 100% of rat carcasses were rapidly colonized by fire ants at high abundances. In our laboratory experiment, the performance of mice-fed fire ant colonies was poor when compared to colonies that were fed mice and insects or insects only. Our results suggest that there is a discrepancy between high levels of fire ant recruitment to vertebrate carrion and the poor colony performance when fed carrion. We hypothesize that fire ants are attracted to vertebrate carrion not because it is a high-quality food, but rather because it hosts large numbers of other invertebrates that can serve as prey for fire ants, potentially showcasing an interesting case of tritrophic interaction in carrion ecology.

Exotic Ants of the Asia-Pacific: Invasion, National Response, and Ongoing Needs

Human activity has facilitated the introduction of many exotic species via global trade. Asia-Pacific countries comprise one of the most economically and trade-active regions in the world, which makes it one of the most vulnerable regions to invasive species, including ants. There are currently over 60 exotic ant species in the Asia-Pacific, with the red imported fire ant, Solenopsis invicta, among the most destructive. Exotic ants pose many economic and ecological problems for the region. Countries in the Asia-Pacific have dealt with the problem of exotic ants in very different ways, and there has been an overall lack of preparedness. To improve the management of risks associated with invasive ants, we recommend that countries take action across the biosecurity spectrum, spanning prevention, containment, and quarantine. The creation of an Asia-Pacific network for management of invasive ants should help prevent their introduction and mitigate their impacts. Expected final online publication date for the Annual Review of Entomology, Volume 67 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Distinct colony boundaries and larval discrimination in polygyne red imported fire ants (Solenopsis invicta)

Evaluating the factors that promote invasive ant abundance is critical to assess their ecological impact and inform their management. Many invasive ant species show reduced nestmate recognition and an absence of boundaries between unrelated nests, which allow populations to achieve greater densities due to reduced intraspecific competition. We examined nestmate discrimination and colony boundaries in introduced populations of the red imported fire ant (Solenopsis invicta; hereafter, fire ant). Fire ants occur in two social forms: monogyne (colonies with a single egg-laying queen) and polygyne (colonies with multiple egg-laying queens). In contrast with monogyne nests, polygyne nests are thought to be interconnected due to the reduced antagonism between non-nestmate polygyne workers, perhaps because polygyne workers habituate the colony to an odor unique to Gp-9-carrying adults. However, colony boundaries and nestmate discrimination are poorly documented, particularly for worker-brood interactions. To delimit boundaries between field colonies, we correlated the exchange of a N-glycine tracer dissolved in a sucrose solution with social form. We also evaluated nestmate discrimination between polygyne workers and larvae in the laboratory. Counter to our expectations, polygyne colonies behaved identically to monogyne colonies, suggesting both social forms maintain strict colony boundaries. Polygyne workers also preferentially fed larval nestmates and may have selectively cannibalized non-nestmates. The levels of relatedness among workers in polygyne colonies was higher than those previously reported in North America (mean ±SE: 0.269 ± 0.037). Our study highlights the importance of combining genetic analyses with direct quantification of resource exchange to better understand the factors influencing ant invasions.

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.