Quantitative analysis and characterization of floral volatiles, and the role of active compounds on the behavior of Heortia vitessoides.

This study explores the role of floral volatile organic compounds (FVOCs) in insect behavior, focusing on Aquilaria sinensis (AS), a valuable tropical plant threatened by Heortia vitessoides Moore. Despite H. vitessoides' attraction to AS and non-host plants like Elaeocarpus decipiens (ED) and Dalbergia odorifera (DO), little is known about their chemical interactions. FVOCs from these plants were analyzed at 9:00 and 18:00 using GC×GC-QTOF-MS and HS-SPME. The results showed that ED exhibiting the highest concentration (92.340 ng/mg), followed by DO (75.167 ng/mg) and AS (64.450 ng/mg). Through GC-EAD and EAG, a total of 11 FVOC compounds with electrophysiological activates were identified. These compounds, except linalool, showed dose-dependent responses. Y-Tube bioassays confirmed phenylethyl alcohol or the mixture of EAD-active compounds produced positive chemotactic responses in both males and females. FVOCs have the potential to be used as a natural and sustainable alternative to chemical insecticides in pest control.

Structure, Synthesis, and Bioassays of Sex Pheromone for Pyrausta machaeralis (Lepidoptera: Crambidae).

The leaf skeletonizer, Pyrausta machaeralis (Lepidoptera: Crambidae), is a serious insect pest of teak (Tectona grandis) in China. The application of insect pheromones is widely applied as an environmentally friendly technology for integrated pest management (IPM). In the present study, crude extracts of sex pheromone glands of calling P. machaeralis females were collected and then analyzed using gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography-mass spectrometry (GC-MS). The combination of infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectrometry was used for structure identification. Afterward, their electrophysiological and behavioral activity was evaluated in the laboratory and field. Herein, we eventually determined two active components, E-11-tetradecenyl acetate (E11-14:Ac) and Z-11-tetradecenyl acetate (Z11-14:Ac), at a ratio of 96:4, as the sex pheromone of P. machaeralis. The identification of sex pheromones would facilitate the development of efficient strategies for monitoring and controlling the field populations of P. machaeralis.

Gregariousness in lepidopteran larvae.

The gregarious lifestyle of lepidopteran larvae is diverse and shaped by a complex interplay of ecological and evolutionary factors. Our review showed that the larval-aggregation behavior has been reported in 23 lepidopteran families, indicating multiple evolution of this behavior. Some larvae live in sibling groups throughout all larval instars and even pupation stages, which may result from the kin-selection. In contrast, group fusion may occur among different sibling or foraging groups of larvae and form larger aggregates, and the gregariousness of these species might be driven by the group-selection. While group size and foraging patterns vary greatly across species, it is generally associated with improved larval survivorship and accelerated development. However, the advantages of group living, such as facilitating feeding activities, adjusting the temperature, and defending natural enemies, may diminish along with development, with strong intraspecific competition occurring at later instars, even when food is abundant. Therefore, the group sizes and fission-fusion dynamics of certain gregarious lepidopteran larvae may be a consequence of their cost-benefit balance depending on various biotic and abiotic factors. Trail and aggregation pheromones, silk trails, or body contact contribute to collective movement and group cohesion of gregarious lepidopteran larvae. However, frequent contact among group members may cause the horizontal transmission of pathogens and pesticides, which may bring an integrated pest management strategy controlling gregarious lepidopteran pests.

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.

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.

Lethal, transmission, behavioral, and physiological effects of Metarhizium anisopliae against gregarious larvae of Heortia vitessoides and synergistic effects between Metarhizium anisopliae and insecticides.

BACKGROUND: Heortia vitessoides Moore is a severe pest of Aquilaria sinensis (Lour.) Gilg, an important source of agarwood. In recent years, large amounts of chemical insecticides have been applied in A. sinensis plantations to deal with the outbreak of H. vitessoides, causing residue problems that reduce the quality and price of agarwood. Herein, we hypothesize that the widely applied biocontrol agent, Metarhizium anisopliae (Metschn.) Sorokin, can effectively kill the gregarious larvae of H. vitessoides through direct contact and horizontal transmission. RESULTS: At the concentration of 1 × 109 conidia/mL, the three M. anisopliae strains caused 100% mortality of H. vitessoides larvae. In addition, mixing donor larvae (previously treated with M. anisopliae conidia) with receptor larvae (which did not directly contact M. anisopliae conidia) caused significantly higher mortality of receptor larvae than the control receptors. This is due to the horizontal transmission of M. anisopliae conidia among live larvae, which was proven by pictures taken by scanning electron microscopy and induced activities of immunity-related enzymes of donor and receptor larvae. Behavioral bioassays showed that M. anisopliae conidia had little effect on the aggregation tendency of H. vitessoides larvae but may trigger feeding-avoidance behavior depending on M. anisopliae strains and concentrations. Interestingly, joint use of sublethal concentrations of M. anisopliae and chemical insecticides significantly increased larval mortality than each agent alone, indicating synergistic effects between M. anisopliae and insecticide against H. vitessoides. CONCLUSION: This study may provide a new strategy to suppress H. vitessoides population and reduce the use of chemical insecticides. © 2023 Society of Chemical Industry.

Toxicological, Behavioral, and Horizontal Transfer Effects of Cycloxaprid Against Formosan Subterranean Termites (Blattodea: Rhinotermitidae).

Cycloxaprid, 9-((6-chloropyrid-3-yl)methyl)-4-nitro-8-oxa-10,11-dihydroimidazo-[2,3-a]-bicyclo-[3,2,1]-oct-3-ene, is a cis-configuration neonicotinoid insecticide. In the present study, the lethal and sublethal effect of cycloxaprid against Formosan subterranean termites, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), was evaluated and compared with fipronil. Toxicity bioassays showed that cycloxaprid had slightly lower toxicity than fipronil. The minimum cycloxaprid concentration in sand and soil that causes 100% termite mortality was 100 ppm. Similar to fipronil, cycloxaprid significantly reduced wood consumption and tunneling activities of termites. In the tunneling-choice tests, termite tunneling activity measured in both length and area was significantly lower in sand treated with cycloxaprid (10 or 100 ppm) than that in untreated sand. In the aggregation-choice tests, cycloxaprid exhibited inhibition to termite aggregation starting from 100 ppm. In addition, cycloxaprid exhibited significant horizontal transfer effect at 10 ppm. In conclusion, our study showed that cycloxaprid is slightly less toxic than fipronil and more repellent to C. formosanus than fipronil. Future studies are needed to evaluate the effectiveness of cycloxaprid against subterranean termites in the field.

Fine Structure of the Visual System of Arge similis (Hymenoptera, Argidae).

External morphology and ultrastructure of the visual system of Arge similis (Vollenhoven, 1860) adults were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Each compound eye contains 2022 ± 89 (mean ± SE) facets in males and 2223 ± 52 facets in females. Arge similis has an apposition kind of compound eye composed of a cornea, a crystalline cone of four cone cells, and a centrally fused rhabdom made up of the rhabdomeres of eight large retinular cells. Each crystalline cone is surrounded by primary and secondary pigment cells with black spherical screening pigment granules measuring 0.60 ± 0.02 and 0.41 ± 0.01 µm in diameter, respectively. Based on our findings, the compound eye of A. similis can be expected to exhibit high adaptability to light intensity changes.

Toxicity, horizontal transfer, and physiological and behavioral effects of cycloxaprid against Solenopsis invicta (Hymenoptera: Formicidae).

BACKGROUND: The red imported fire ant, Solenopsis invicta Buren, is a significant urban, agricultural, and medical pest with a wide distribution in the world. Surface or mound treatment using contact insecticide is one of the main methods to control S. invicta. In the present study, cycloxaprid, a newly discovered neonicotinoid insecticide, was evaluated for S. invicta control and compared with two referent insecticides, imidacloprid and bifenthrin. RESULTS: Surfaces or sand treated with cycloxaprid, imidacloprid, or bifenthrin caused high mortality of S. invicta workers, and the action of cycloxaprid or imidacloprid was slower than bifenthrin. Like imidacloprid and bifenthrin, cycloxaprid can be horizontally transferred from corpses or live donor ants to recipient ants. In addition, cycloxaprid- or imidacloprid-treated surfaces significantly induced the activities of acetylcholinesterase (AChE) and detoxification enzymes; nevertheless, they had no significant effect on the foraging behaviors of S. invicta workers. Also, sand treated with cycloxaprid or imidacloprid did not negatively affect the digging activities of ants. Interestingly, S. invicta workers excavated significantly more sand containing 0.01 mg/kg cycloxaprid than untreated sand in the no-choice digging bioassays. In addition, extensive nesting activities (sand excavation and stacking) were observed in the flowerpots containing untreated sand or sand treated with cycloxaprid or imidacloprid. On the contrary, bifenthrin significantly reduced the foraging, digging, and nesting activities of S. invicta workers. CONCLUSION: Cycloxaprid is a slow-acting and nonrepellent insecticide against S. invicta workers, and its contact and horizontal toxicities are slightly higher than imidacloprid. © 2022 Society of Chemical Industry.

Lateral Transmission of Yeast Symbionts Among Lucanid Beetle Taxa.

To deepen understanding the evolutionary process of lucanid-yeast association, the lateral transmission process of yeast symbionts among stag beetle genera Platycerus and Prismognathus around the border between Japan and South Korea was estimated based on molecular analyses and species distribution modelings. Phylogenetic analyses were based on yeast ITS and IGS sequences and beetle COI sequences using Prismognathus dauricus from the Tsushima Islands and Pr. angularis from Kyushu, Japan, as well as other sequence data from our previous studies. The range overlap based on the species distribution model (SDM) and differentiation in ecological space were analyzed. Based on the IGS sequences, Clade II yeast symbionts were shared by Platycerus hongwonpyoi and Pr. dauricus in South Korea and the Tsushima Islands, and Platycerus viridicuprus in Japan. Clade III yeasts were shared by Pr. dauricus from the Tsushima Islands and Pr. angularis in Japan. During the Last Interglacial period when the land bridge between Japan and the Korean Peninsula existed, range overlap was predicted to occur between Pl. viridicuprus and Pr. dauricus in Kyushu and between Pr. dauricus and Pr. angularis in Kyushu and the Tsushima Islands. The ecological space of Pl. hongwonpyoi was differentiated from that of Pl. viridicuprus and Pr. angularis. We demonstrated the paleogeographical lateral transmission process of Scheffersomyces yeast symbionts among lucanid genera and species: putative transmission of yeasts from Pr. dauricus to Pl. viridicuprus in Kyushu and from Pr. angularis to Pr. dauricus in Kyushu or the Tsushima Islands. We also found that the yeast symbionts are likely being replaced in Pr. dauricus on the Tsushima Islands. We present novel estimates of the lateral transmission process of microbial symbionts based on phylogenetic, SDM and environmental analyses among lucanid beetles.

Diverse Heat Tolerance of the Yeast Symbionts of Platycerus Stag Beetles in Japan.

The genus Platycerus (Coleoptera: Lucanidae) is a small stag beetle group, which is adapted to cool-temperate deciduous broad-leaved forests in East Asia. Ten Platycerus species in Japan form a monophyletic clade endemic to Japan and inhabit species-specific climatic zones. They are reported to have co-evolutionary associations with their yeast symbionts of the genus Sheffersomyces based on host cytochrome oxidase subunit I (COI) and yeast intergenic spacer (IGS) phylogenies. Here we examined the heat tolerances of the yeast colonies isolated from the mycangia of 37 females belonging ten Japanese Platycerus species. The upper limits of growth and survival temperatures of each colony were decided by cultivating it at ten temperature levels between 17.5 and 40°C. Although both temperatures varied during 25.0-31.25°C, the maximum survival temperatures (MSTs) were a little higher than the maximum growth temperatures (MGTs) in 16 colonies. Pearson's correlations between these temperatures and environmental factors (elevation and 19 bioclimatic variables from Worldclim database) of host beetle collection sites were calculated. These temperatures were significantly correlated with elevation negatively, the maximum temperature of the warmest month (Bio5) positively, and some precipitative variables, especially in the warm season (Bio12, 13, 16, 18) negatively. Sympatric Platycerus kawadai and Platycerus albisomni share the same lineage of yeast symbionts that exhibit the same heat tolerance, but the elevational lower range limit of P. kawadai is higher than that of P. albisomni. Based on the field survey in their sympatric site, the maximum temperature of host wood of P. kawadai larvae is higher about 2-3°C than that of P. albisomni larvae in the summer, which may restrict the elevational range of P. kawadai to higher area. In conclusion, it is suggested that the heat tolerance of yeast symbionts restricts the habitat range of their host Platycerus species or/and that the environmental condition that host Platycerus species prefers affect the heat tolerance of its yeast symbionts.

Electrophysiological and behavioral responses of red imported fire ants (Hymenoptera: Formicidae) to an essential balm and its components.

BACKGROUND: An over-the-counter medicine product of China known as essential balm effectively repelled red imported fire ants, Solenopsis invicta Buren. However, it was not clear which chemical component(s) accounted for the repellency, and whether they would effectively repel S. invicta in the field. RESULTS: Five components, eucalyptol, camphor, menthol, methyl salicylate, and eugenol, were identified in essential balm using gas chromatography-mass spectrometry (GC-MS). Each component elicited concentration-dependent electroantennography (EAG) response. Under field conditions, all components showed repellency against foraging ants. Interestingly, foraging ants managed to access the food items placed on a surface smeared with eucalyptol, camphor, menthol, or methyl salicylate by depositing soil particles on the surface and then walking on soil particles. However, they failed to do so when the surface was smeared with eugenol. Repellency of eugenol lasted for > 24 h, which was much longer than that of the other four components of essential balm and is comparable to that of N,N-diethyl-m-toluamide (DEET), the standard for insect repellants. CONCLUSION: Olfactory response of S. invicta to all five components of the essential balm was confirmed. Each component showed repellency against S. invicta workers in the field. However, only eugenol significantly suppressed both foraging and particle-covering behavior within 24 h. The repellent effect of eugenol lasted much longer than the other four components. Particle-covering behavior has been largely ignored in studying fire ant repellants. Our study demonstrated that it is necessary to consider such behaviors in ant repellent bioassays in the future. © 2020 Society of Chemical Industry.

Red imported fire ants (Hymenoptera: Formicidae) cover inaccessible surfaces with particles to facilitate food search and transportation.

Eusocial insects have evolved diverse particle-use behaviors. A previous study reported that red imported fire ants, Solenopsis invicta Buren, deposited soil particles on substances treated with essential balm, a fire ant repellent. We hypothesized that S. invicta modifies inaccessible surfaces by covering them with soil particles to facilitate food search and transportation. Here, laboratory experiments were conducted to study the particle-covering behavior of S. invicta in response to viscose surfaces or surfaces treated with essential balm or liquid paraffin in the presence of real food (sausage) or non-food objects (acrylic plates). S. invicta workers deposited significantly more soil particles on these three types of treated surfaces than on untreated surfaces. In addition, significantly more particles were relocated on viscose and paraffin-smeared surfaces in the presence of food than in the presence of non-food objects. The particle-covering behavior on viscose surfaces was also observed in the field. Interestingly, when no soil particles were available, ants searched and transported food on viscose surfaces only if the surfaces were artificially covered with sufficient quantities of soil particles but could not do so on viscose surfaces without soil particles or with insufficient quantities of soil particles. In addition, ants actively relocated particles to cover viscose surfaces if the transportation distance was within 200 mm, whereas significantly fewer particles were relocated at longer transportation distances (400 mm). Our study provides a novel example of particle use by fire ants during foraging.

Effects of clay materials and moisture levels on habitat preference and survivorship of Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae).

Formosan subterranean termites, Coptotermes formosanus Shiraki, usually transport clay materials into tree hollows and bait stations. Our previous research showed that C. formosanus preferred to aggregate in the locations containing field-collected clay samples, but it was not clear whether this preference was influenced by clay types and/or moisture. In the present study, we conducted multiple-choice tests under low-moisture (25% moisture) or moderate-moisture (50% moisture) conditions to evaluate the aggregation and wood-feeding preferences of C. formosanus responding to hollow wooden cylinders (simulation of tree hollows) or baiting containers (simulation of bait stations) filled with different clay materials (bentonite , kaolin, chlorite, illite, or attapulgite), soil, or unfilled. Under low-moisture conditions, the majority of termites were found in the wooden cylinders or baiting containers filled with bentonite. Under moderate-moisture conditions, however, termites preferred to aggregate in wooden cylinders filled with chlorite or attapulgite; the percentages of termites that stayed in baiting containers filled with chlorite, attapulgite or soil were similar, which were significantly higher than those that filled with kaolin, illite, or unfilled. We then conducted no-choice tests to study the effect of clay materials on termites. Under low-moisture conditions, clay filled in the baiting containers significantly increased survivorship and body water percentage (an indicator of termite vigor) of termites, whereas no similar effect was detected under moderate-moisture conditions. This study demonstrated that both clay type and moisture affect termites' preference.

Ultrastructure of Antennal Morphology and Sensilla of Teak Skeletonizer, Eutectona machaeralis Walker (Lepidoptera: Crambidae).

The leaf skeletonizer, Eutectona machaeralis (Walker) (Lepidoptera: Crambidae), is a severe insect pest of teak trees (Tectona grandis L.f.) in China. To provide some basic evidence for future semiochemical-based management strategies of E. machaeralis, the morphology, ultrastructure, and distribution of antennal sensilla of adults were observed under scanning and transmission electron microscopy. The shape and structure of antenna were similar between males and females, both being filiform. However, the antennal length of males was significantly longer than that of females. Eight morphological sensilla types were observed in both sexes: Böhm's bristles, sensilla trichodea, sensilla basiconica, sensilla chaetica, sensilla styloconica, sensilla coeloconica, sensilla auricillica, and sensilla squamiformia. Significant sexual dimorphism of the sensilla dimensions was found, especially in sensillar length. The putative and potential functions of the different sensilla types are discussed based on the fine structures of the cuticular walls and dendrites of the different sensilla types. We expect these results to help lay a solid foundation for future functional research and develop further investigations of E. machaeralis.

Trichoderma Species Attract Coptotermes formosanus and Antagonize Termite Pathogen Metarhizium anisopliae.

Although subterranean termites live within soil, little attention has been paid on the potential interaction among subterranean termites and soil microbes. Herein, we conducted different choice tests to investigate aggregation and tunneling behaviors of Coptotermes formosanus Shiraki responding to soil/sand treated with conidia of seven soil fungi, Trichoderma longibrachiatum Rifai, Trichoderma koningii Oud., Trichoderma hamatum (Bon.) Bain., Trichoderma atroviride Karsten, Trichoderma spirale Indira and Kamala, Trichoderma harzianum Rifai, and Trichoderma viride Pers. ex Fries. In aggregation-choice test, soil treated with nearly all Trichoderma species tested (except T. koningii) significantly increased termite aggregation compared with untreated soil. In tunneling-choice tests, termites produced significantly larger tunnels in sand treated with T. longibrachiatum or T. koningii than that in untreated sand. We hypothesized that Trichoderma species could benefit termites by protecting them from infection of the entomopathogenic fungus Metarhizium anisopliae (Metschn) Sorokin, and three Trichoderma species that attracted termites (T. longibrachiatum, T. atroviride, and T. harzianum) were tested. The antagonism tests showed that the three Trichoderma species suppressed growth of M. anisopliae. Also, the median lethal time (LT50) of termites exposed to both Trichoderma species and M. anisopliae was significantly longer than termites exposed to M. anisopliae alone. Interestingly, though significantly fewer termites aggregated in soil treated with M. anisopliae conidia compared with untreated soil, M. anisopliae conidia mixed with T. longibrachiatum or T. harzianum were no longer repellent to termites. Our results showed that the fungi in the genus Trichoderma (1) exerted generally attractive effects on termites, (2) protected termites from the infection of entomopathogenic fungus, and (3) altered pathogen-avoiding behaviors of termites. Future studies will be required to understand the mechanisms underlying these newly discovered effects.

Morphological and optical features of the apposition compound eye of Monochamus alternatus Hope (Coleoptera: Cerambycidae).

The Japanese pine sawyer beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae) is currently the most destructive forest pest as it transmits the pine wilt nematode Bursaphelenchus xylophilus. Morphological, optical features and dark/light adaptational changes of the compound eyes of M. alternatus adults were examined by light, scanning and transmission electron microscopy. The eye of M. alternatus is apposition type and contains 489-712 ommatidia, depending on the beetle's body size. Each ommatidium features a large corneal lens, composed of a thick inner lens (ILU) and a thin outer lens unit (OLU); an acone-type of cone of four cone cells, a semi-fused type of rhabdom formed by eight retinular cells (two central cells: R7-R8 surrounded by six peripheral cells: R1-R6). Dark/light adaptational changes affect size and shape of the cones as well as the rhabdom's cross-sectional area and outline, to optimize the amount of light that reaches the photopigment. The compound eyes of M. alternatus have an F-number of 0.94, an interommatidial angle of 5.34°, an eye parameter P of 4.98 µm rad and a ratio of acceptance to interommatidial angle of 0.45. The eye is characterized by relatively poor spatial resolution, but can be expected to exhibit high absolute sensitivity and contrast in dim light.

Food Transport of Red Imported Fire Ants (Hymenoptera: Formicidae) on Vertical Surfaces.

Many ants can cooperatively transport large food items (either coordinated or uncoordinated during transportation), which can be rarely observed in other animals besides humans. Although these behaviors have been extensively investigated on horizontal surfaces, few studies dealt with food transport on vertical surfaces. The red imported fire ant, Solenopsis invicta Buren, is an invasive ant species that commonly forages on trees. Our studies showed that S. invicta used multiple strategies to transport food items on vertical surfaces (tree trunks). Small food items (1 × 1 × 1 mm sausage) were carried and transported by individual ants, and larger food items were either collectively and directly transported or cut collaboratively first and small particles were then transported individually or collectively. Competition and deadlocks were frequently observed during individual and collective transport respectively. During cutting, groups of ants tightly fixed the food on the tree trunks by holding the edges of the food item, while other ants cut the food into smaller particles. All food items and particles were moved downward. We investigated the effects of food placement (placed on a platform or fixed on tree trunk), food shape (cuboid or flattened), particle sizes (0.45-1, 1-2, 2-3, or 3-4 mm), and placement height (20, 80, or 150 cm) on the food transport on tree trunks. Our studies are the first to show how fire ants transport food on a vertical surface, and may provide insights into the development of novel fire ant baiting systems that can be placed on tree trunks.

Food-burying behavior in red imported fire ants (Hymenoptera: Formicidae).

The food-burying behavior has been reported in many mammals and birds, but was rarely observed in invertebrates. The red imported fire ants, Solenopsis invicta Buren, is an invasive pest in many areas of the world that usually performing food-burying during the foraging processes. However, the impacted factors and measureable patterns of this behavior is largely unknown. In the present study, food-burying vs food-transport behaviors of Solenopsis invicta were observed under laboratory and field conditions. When starved (no food was provided for 37 days) in the laboratory, food (sausage) was consumed by large numbers of ants, and few burying behaviors were observed. However, when food was provided until satiation of the colonies, food-transport was suppressed and significantly more soil particles were relocated on the food and graph paper square (where the food was placed) when compared with these colonies exposed to starved conditions. Videotapes showed that soil particles (1.47 ± 0.09 mm2) were preferentially placed adjacent to (in contact with) the food items at the beginning; and after the edges were covered, ants transported significantly smaller soil particles (1.13 ± 0.06 mm2) to cover the food. Meanwhile, larger particles (1.96 ± 0.08 mm2) were pulled/dragged around (but not in contact with) the food. Interestingly, only a small number of ants, mainly the small workers, were involved in food-burying, and the ants tended to repeatedly transport soil particles. A total of 12 patterns of particle transport were identified, and soil particles were most frequently picked from the foraging arena and subsequently placed adjacent to the food. In the field, almost all released food was actively transported by Solenopsis invicta workers, and no burying behavior was observed. Our results show that the food-burying behavior of Solenopsis invicta may be associated with the suppressed foraging activity, and the burying task may be carried out by certain groups of workers.

Effect of Polyacrylamide/Attapulgite Composite on Foraging Behaviors of Formosan Subterranean Termites (Blattodea: Rhinotermitidae).

Moisture conditions of food and soil are essential for the survival and foraging activities of subterranean termites. Polyacrylamide/attapulgite composite is a water-retaining agent that has been applied to increase moisture of agricultural soils. We hypothesize that polyacrylamide/attapulgite composite may increase the moisture of bait matrixes and soil surrounding baiting containers and therefore attract termites and increase their foraging activities. In the present study, aggregation and feeding preferences, survivorship, body water percentage, and wood consumption of Formosan subterranean termites, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), were investigated when responding to polyacrylamide/attapulgite composite that was buried within soil (substrate) or filled in the void volume of baiting containers. Two-choice tests showed that termites consumed significantly more wood when polyacrylamide/attapulgite composite was buried within dry soil (27%-moisture) than the controls (no polyacrylamide/attapulgite composite was provided). However, polyacrylamide/attapulgite composite buried within wet soil (54%-moisture) did not significantly affect foraging behaviors of termites. Multiple-choice tests showed no aggregation or feeding preference of termites in the baiting containers filled with polyacrylamide/attapulgite composite compared with the soil-filled or unfilled ones, whenever the substrate was dry or wet. No-choice tests showed that the presence of polyacrylamide/attapulgite composite (buried within soil or filled in baiting containers) significantly increased wood consumption and body water percentage of termites as well as wood moisture under dry-substrate conditions. Our studies suggest that burying polyacrylamide/attapulgite composite within dry soil may enhance foraging activities of termites, but filling the bait stations with polyacrylamide/attapulgite composite may not effectively attract termites.