Sugar responsiveness could determine foraging patterns in yellowjackets.

Sympatric-related species often exhibit resource partitioning. This can occur through different mechanisms, such as behavioral, morphological, and sensory variations, leading to qualitative, temporal, or spatial differences in resource exploitation, such as consuming different types of food. Sensory-based niche partitioning could be the underlying mechanism through which closely related species effectively reduce niche overlap. Here we ask whether variations in sensory responses to carbohydrates could reflect differences in the foraging patterns of two Vespula species present in Patagonia. For this, we established (i) the response thresholds toward carbohydrate solutions of foraging V. germanica and V. vulgaris in the laboratory, (ii) the sugar concentration of foraged carbohydrates in the field, and (iii) possible effects of incoming sugar concentration and performance at individual and colony levels. Results indicate a higher sucrose response threshold in V. germanica than V. vulgaris. Field results indicate that higher carbohydrate concentrations foraged by V. germanica, with 57% of V. germanica foragers returning with concentrations above 50% w/w, while only 23% of V. vulgaris foragers did so. These differences in sucrose sensitivity and foraging patterns positively correlate with colony size, irrespective of the species. Our results suggest that competition could be reduced in these closely related invasive social wasp species through sensory differences in their sugar perception levels, which would lead to them foraging different carbohydrate sources. This study suggests that sensory niche partitioning could promote species coexistence in these social wasps.

Honeydew production by the giant willow aphid (Tuberolachnus salignus, Hemiptera: Aphididae) and its effect on foraging yellowjackets (Hymenoptera: Vespidae).

BACKGROUND: Understanding the factors that promote the success of invasive species is important for managing biological invasions. Interactions between invasives and other species (e.g. competitors, pathogens, or predators), could favor or limit their success. In recent decades, yellowjacket wasps, including Vespula germanica and Vespula vulgaris, have successfully established in Patagonia. Additionally, the invasive willow Salix fragilis has invaded areas next to watercourses, which in turn are typically colonized by the giant willow aphid (GWA, Tuberolagnus salignus), an additional species characterized as a successful invader in many regions worldwide. Aphid exudate (honeydew) has been reported to be used as a carbohydrate source by social wasps. The aim of our study was to gain a better understanding of the infestation pattern of the GWA in north-western Patagonia, its effect on exudate availability and its relationship with yellowjacket foraging patterns. The study was conducted under the working hypothesis that the increase in the size of GWA colonies and resulting honeydew production, will fuel an increase in local Vespula spp. RESULTS: We found that the aphid honeydew is produced in relatively high amounts in the region (estimated at 1517 ± 139 kg/ha/season), with strong indications that it is used by yellowjackets because of the significantly higher abundance levels of yellowjackets foraging on honeydew compared to nearby areas. CONCLUSION: Given its effect on yellowjacket foraging behavior, the interaction of these three invasive species, willows, GWA and yellowjackets, needs to receive special attention to develop future environmentally-sound mitigation tools of these nuisance pest. © 2023 Society of Chemical Industry.

Microplastics incorporated by honeybees from food are transferred to honey, wax and larvae.

Microplastics (MP) are ubiquitous in the environment, and there is little information available on their impact on terrestrial organisms. Their effect on insects and particularly on honeybees is relevant, given the prevalence of these organisms in the environment and the fact that they provide key ecosystem services. We conducted a field study to assess (1) the fate of these ingested MP within the hive, and (2) MP effect on Apis mellifera population growth during chronic exposure. We aimed to determine if MP ingested by honeybees are incorporated into hive matrices, including honey, and their effect on colony development and honey reserves. We fed beehives with sucrose solutions treated or untreated with 50 mg of Polyester microfibers/L for one month. Microplastic fibers (MF) from treated syrup were incorporated by adult worker bees, remaining in their cuticle, digestive tract, larvae, honey, and wax. Most of the MF were accumulated in wax showing that honey remains as a safe food. At the end of the experiment, no differences in honey reserves or bee population were observed. This is the first study to evaluate in the field the effects and dynamics of MP inside honeybee hives. Our results showed that bees can incorporate MP from the environment and deliver them into the different matrices of the hive. Concentration of MF found in honey of treated hives was like that found in commercial honey, suggesting that honeybees might be exposed to similar MP contamination levels in the environment compared to our experiment. Finally, our results highlight a way in which MP might enter the food chain, with direct implication for human health.

Plant odors trigger clearing behavior in foraging trails- do they represent olfactory obstacles?

Foraging trails of leaf-cutting ants may be exposed to plant material that interferes with foragers' flux either by physically blocking it or due to secondary metabolites which affect insect behavior. We hypothesized that plant secondary metabolites such as plant volatiles may interfere with pheromone communication, triggering clearing behavior. We impregnated small pieces of paper with different plant odors from native and exotic species and placed them in the middle of foraging trails of the leaf-cutting ant Acromyrmex lobicornis. As a control, we used papers impregnated with trail odor. The paper used as substrate for the odors did not constitute a physical obstacle based on its small surface area. Papers treated with trail odor did not interfere with ant flux and were not removed from the trail. However, when papers were treated with plant odors, they were removed from the trail in most of the cases and ant flux was reduced significantly by 15-28%. We found that ants tapped the tip of their gaster against the ground around the treated papers only when they were impregnated with foreign odors. The number of gaster tappings as well as the time between the placement of the paper and its removal increased with plant odor concentration. However, the decision to remove the paper was not correlated with the number of gaster tappings. Interestingly, clearer ants were smaller than forager ants, suggesting there is morphological differentiation in clearing behavior of the trail. Results from the current study also suggest that odors trigger clearing behavior on foraging trails and affect trail marking behavior. Our results provide information about the potential for plant compounds to constitute obstacles, even when they do not physically obstruct the trail. We conclude that odors may trigger clearing behavior by interfering with pheromone communication.

Identification of a novel plant-derived attractant for Acromyrmex lobicornis leaf-cutting ants.

Leaf-cutting ants are considered major pests of agriculture and forestry in the Neotropics. Attractive toxic baits are the prevailing method for managing them. Thus, there is great interest in identifying attractants to incorporate into these baits. Moreover, leaf-cutting ants can avoid toxic baits by associating the attractant with the toxin. We evaluated attractiveness of heptyl butyrate, a volatile compound found in fresh apples and plums. We conducted field experiments with ten colonies of Acromyrmex lobicornis. First, we evaluated the behaviour of ants exposed to heptyl butyrate at 1% by surrounding resources. Then, we compared the attractiveness of heptyl butyrate and orange pulp, the most commonly used attractant. Finally, we evaluated whether heptyl butyrate increases the attractiveness of a carbohydrate resource at varying doses. Heptyl butyrate at 1% attracted 92% more ants than the control and that it was as attractive as orange pulp. Heptyl butyrate paired with sucrose at concentrations of 0.001 and 0.1% was more attractive than sucrose alone, but greater concentrations did not increase sucrose's attractiveness. Therefore, heptyl butyrate could be added to toxic baits to manage A. lobicornis as it is as attractive as the most commonly used attractant and can be applied directly to the pellets.

Effect of Vegetable Oils as Phagostimulants in Adults of Dichroplus vittigerum (Orthoptera: Acrididae).

Several species of grasshoppers are attracted to vegetable oils. These oils have kairomonal properties mainly due to the presence of linolenic and linoleic fatty acids. This study aimed to determine whether the odors of canola, flax, and olive oils are attractive to Dichroplus vittigerum (Blanchard 1851) and if they induce preference and feeding. We conducted three bioassays to determine whether oil modifies attraction and feeding behavior of this grasshopper. We first determined the attraction of the oils using a wind tunnel, secondly evaluated phagostimulation produced by the oils, and finally performed preference tests comparing consumption of Taraxacum officinale (Weber ex F.H.Wigg. 1780, Asterales: Asteraceae) leaves treated with the oils versus control leaves. Even though all of the oils induced attraction, only flax oil acted as a phagostimulant. However, the oils did not determine the preference and did not increase feeding on leaves. We hypothesize that T. officinale leaves are inherently attractive and treatment with oils did not affect feeding on them. Our results provide a starting point to develop baits that can be used to attract and control these harmful insects, presenting flax oil as a potential bait for D. vittigerum since its odor was both attractive and led to increased feeding or phagostimulation. Future studies should test the effect of the oils on other plant species or at varying doses, under field conditions.

Testing the Insecticidal Activity of Nanostructured Alumina on Sitophilus oryzae (L.) (Coleoptera: Curculionidae) Under Laboratory Conditions Using Galvanized Steel Containers.

Most stored-grain pest insects increase their population within a relatively short time, causing serious damage to stored products. Sitophilus oryzae (L.) is one of the world's major stored-grain pest insects and was chosen as the model insect for our studies. This study compared the efficacy of three different dusts under laboratory conditions: aluminum dust (nanostructured alumina), DiatomiD®, and Protect-It® (commercial diatomaceous earth). Parental survival, grain damage, and progeny production were measured at 250 and 500 ppm in treated wheat. The tests were conducted in 400 mL galvanized steel jars, an experimental model used for the first time to measure the effectiveness of nanostructured alumina, since most studies have been typically performed in small petri dishes. Parental survival obtained was highest in the untreated controls, followed in decreasing order by DiatomiD®, Protect-It®, and nanostructured alumina (NSA). NSA caused the greatest mortality. All treatments significantly reduced grain weight loss and frass production in wheat infested by S. oryzae. The degree of progeny (F1) suppression was directly related to the product and treatment rate, progeny being significantly suppressed by NSA in wheat followed by Protect-It® and DiatomiD®. Therefore, NSA had a greater impact on insect population dynamics.

Social Learning in Vespula Germanica Wasps: Do They Use Collective Foraging Strategies?

Vespula germanica is a social wasp that has become established outside its native range in many regions of the world, becoming a major pest in the invaded areas. In the present work we analyze social communication processes used by V. germanica when exploiting un-depleted food sources. For this purpose, we investigated the arrival pattern of wasps at a protein bait and evaluated whether a forager recruited conspecifics in three different situations: foragers were able to return to the nest (full communication), foragers were removed on arrival (communication impeded), or only one forager was allowed to return to the nest (local enhancement restricted). Results demonstrated the existence of recruitment in V. germanica, given that very different patterns of wasp arrivals and a higher frequency of wasp visits to the resource were observed when communication flow between experienced and naive foragers was allowed. Our findings showed that recruitment takes place at a distance from the food source, in addition to local enhancement. When both local enhancement and distant recruitment were occurring simultaneously, the pattern of wasp arrival was exponential. When recruitment occurred only distant from the feeder, the arrival pattern was linear, but the number of wasps arriving was twice as many as when neither communication nor local enhancement was allowed. Moreover, when return to the nest was impeded, wasp arrival at the bait was regular and constant, indicating that naive wasps forage individually and are not spatially aggregated. In conclusion, this is the first study to demonstrate recruitment in V. germanica at a distance from the food source by modelling wasps' arrival to a protein-based resource. In addition, the existence of correlations when communication was allowed and reflected in tandem arrivals indicates that we were not in the presence of random processes.

Novel use of nanostructured alumina as an insecticide.

BACKGROUND: The worldwide need to produce an inexpensive and abundant food supply for a growing population is a great challenge that is further complicated by concerns about risks to environmental stability and human health triggered by the use of pesticides. The result is the ongoing development of alternative pest control strategies, and new, lower-risk insecticidal molecules. Among the recent technological advances in agricultural science, nanotechnology shows considerable promise, although its development for use in crop protection is in its initial stages. RESULTS: This study reports for the first time the insecticidal effect of nanostructured alumina. Two species were used as model organisms, Sitophilus oryzae L. and Rhyzopertha dominica (F.), which are major insect pests in stored food supplies throughout the world. Both species experienced significant mortality after 3 days of continuous exposure to treated wheat. Nine days after treatment, the median lethal doses (LD(50)) observed ranged from 127 to 235 mg kg(-1). CONCLUSION: Comparison of these results with recommended rates for commercial insecticidal dusts suggests that inorganic nanostructured alumina may provide a cheap and reliable alternative for control of insect pests. This study expands the frontiers for nanoparticle-based technologies in pest management. Further research is needed to identify its mode of action and its non-target toxicity, and to determine the potential of other nanostructured materials as pest control options for insects.