Sucrose Baits Research Articles

Partner supply mediates elevational gradients in the outcome of ant‐hemipteran mutualistic associations

AbstractAimAlong elevational or latitudinal gradients, the dynamics of mutualistic interactions may be driven by shifts in partner abundance, themselves driven by changes in environmental factors. We test the hypothesis that partner abundance mediates the frequency of associations and investment incurred by partners while associating.LocationWestern and Eastern slopes of the Andes of Ecuador.TaxonAnts (Hymenoptera, Formicidae) and treehoppers (Hemiptera, Membracidae).MethodsUsing a combination of visual surveys and sucrose baits, we scored the abundance of ants, treehoppers, and their associations at 500‐meter intervals along two 4000 m elevational gradients in the equatorial Andes (three locations per elevation interval, two 70 m transects per location). We used the size of the treehopper aggregations and of the ant worker force involved in the associations as proxies for the investment partners incur in the interaction. We analysed our data using GLMM with transects as units of analyses and locations as random effects.ResultsWe show that the number of ant‐treehopper aggregations declined with elevation, in parallel with a decline in the abundance of both partners, but with ants declining at a faster rate. Despite this, the numbers of ants and treehoppers within individual aggregations increased with elevation, but this time with the number of treehoppers in the aggregations increasing at a faster rate.Main conclusionWe suggest that this elevational gradient in the size of ant‐treehopper aggregations arises from consumer resource‐dynamics, where the partner in short supply elicits greater investment from the other. Within the range of elevations where the interaction is possible, the observation that a smaller proportion of treehopper species engage in mutualism at higher elevations further suggests decreasing benefits of the associations with elevation. Our study suggests that the geography of abundance and supply, and its consequences on cost and demand of services, may dictate the outcome of mutualistic interactions along gradients, with possible implications for the maintenance of biological diversity.

Biodegradable alginate hydrogel bait delivery system effectively controls high-density populations of Argentine ant in commercial citrus

The Argentine ant, Linepithema humile (Mayr), poses a significant economic threat to citrus production in southern California. Broad-spectrum insecticide sprays provide poor ant control and present a hazard to human and environmental health. Liquid sucrose bait infused with a low concentration of insecticide is an effective alternative treatment but current approaches require considerable economic investment in plastic dispensers and continual maintenance. To produce a baiting product for control of L. humile suitable for large-scale application, a biodegradable, broadcastable alginate hydrogel for delivery of aqueous low-dose thiamethoxam sucrose bait was developed and evaluated in replicated field trials in commercial citrus groves. Ant activity was significantly reduced in hydrogel-treated trees. Peak L. humile suppression was achieved 48 h following the final hydrogel disbursement, with an estimated 91% reduction in activity from baseline estimates and a 17-fold lower activity in treated trees in comparison with untreated trees. Significant residual activity of the hydrogel treatments was recorded, with a nearly 70% reduction from pre-treatment levels persisting at least 3 weeks after the last application. We conclude that alginate hydrogels can provide excellent control of L. humile while deploying 99.99% less insecticide into orchards than commercial barrier spray treatments.

Using metabolic and thermal ecology to predict temperature dependent ecosystem activity: a test with prairie ants.

As ecosystems warm, ectotherm consumer activity should also change. Here we use principles from metabolic and thermal ecology to explore how seasonal and diel temperature change shapes a prairie ant community's foraging rate and its demand for two fundamental resources: salt and sugar. From April through October 2016 we ran transects of vials filled with solutions of 0.5% NaCl and 1% sucrose. We first confirm a basic prediction rarely tested: the discovery rate of both food resources accelerated with soil temperature, but this increase was typically capped at midday due to extreme surface temperatures. We then tested the novel prediction that sodium demand accelerates with temperature, premised on a key thermal difference between sugar and sodium: sugar is stored in cells, while salt is pumped out of cells proportional to metabolic rate, and hence temperature. We found strong support for the resulting prediction that recruitment to NaCl baits accelerates with temperature more steeply than recruitment to 1% sucrose baits. A follow up experiment in 2017 verified that temperature-dependent recruitment to sucrose concentrations of 20% (mimicking rich extrafloral nectaries), while noisy, was still only half as temperature dependent as recruitment recorded for 0.5% NaCl. These results demonstrate how ecosystem warming accelerates then curtails the work done by a community of ectotherms, and how the demand and use of fundamental nutrients can be differentially temperature dependent.

Bait visitation by Formica lemani (Hymenoptera: Fomicidae) indicates shortage of carbohydrates in alpine grasslands

Insights can be gained by analysing the feeding decisions of animals in terms of nutrient demands at a species or community level. Using carbohydrate and protein food baits, resource use and food preferences of Formica (Serviformica) lemani were determined at nine locations situated at different altitudes (1875 to 2400 m a.s.l.) in the alpine grassland belt above the tree line in Austria and northern Italy. F. lemani is the most common species of ant in this habitat. Sucrose baits placed around ant colonies were visited by significantly (3.9 times) more workers than protein baits. This indicates that sources of sugar (carbohydrate) are in short supply in the alpine zone, whereas availability of prey items appears to be less constraining. Overall, we recorded a decrease in the incidence of visits to baits from low (31.9% baits attracting ants at least once) to high altitudes (16.7%). Foraging ants never visited 51.5% of the baits exposed for periods of 75 min. This indicates that with increasing altitude competition for food among ant colonies becomes less intense in alpine grassland ant communities.

Dose response of red imported fire ant colonies to Solenopsis invicta virus 3.

Baiting tests were conducted to evaluate the effect of increasing Solenopsis invicta virus 3 (SINV-3) dose on fire ant colonies. Actively growing early-stage fire ant (Solenopsis invicta Buren) laboratory colonies were pulse-exposed for 24 hours to six concentrations of SINV-3 (10(1), 10(3), 10(5), 10(7), 10(9) genome equivalents/μl) in 1 ml of a 10 % sucrose bait and monitored regularly for two months. SINV-3 concentration had a significant effect on colony health. Brood rating (proportion of brood to worker ants) began to depart from the control group at 19 days for the 10(9) concentration and 26 days for the 10(7) concentration. At 60 days, brood rating was significantly lower among colonies treated with 10(9), 10(7), and 10(5) SINV-3 concentrations. The intermediate concentration, 10(5), appeared to cause a chronic, low-level infection with one colony (n = 9) supporting virus replication. Newly synthesized virus was not detected in any fire ant colonies treated at the 10(1) concentration, indicating that active infections failed to be established at this level of exposure. The highest bait concentration chosen, 10(9), appeared most effective from a control aspect; mean colony brood rating at this concentration (1.1 ± 0.9 at the 60 day time point) indicated poor colony health with minimal brood production. No clear relationship was observed between the quantity of plus genome strand detected and brood rating. Conversely, there was a strong relationship between the presence of the replicative genome strand and declining brood rating, which may serve as a predictor of disease severity. Recommendations for field treatment levels to control fire ants with SINV-3 are discussed.

Inter-generic and inter-habitat variation in the demand for sodium by Neotropical ants

Sodium is a potentially limiting element for ant populations. Here we examined the extent to which the demand for sodium varies among different ant genera and habitats. Sucrose and NaCl baits were placed on the ground and in trees located within three types of savanna and one type of forest. Tree-dwelling ants were found ca. two times more often on NaCl than on sugar baits, whereas on ground the frequency of ants on NaCl baits was about 20 % lower than on sugar baits. This difference seems to be explained by compositional differences between the tree- and ground-dwelling faunas. Camponotus and Cephalotes were much more frequent in trees than on ground, and both showed a preference for NaCl over sucrose baits. In contrast, the most frequent ants on the ground were Pheidole, and these were mainly attracted to sucrose baits. Genera-specific patterns of bait use did not differ significantly among habitats in spite of potential differences in the availability of sucrose (in honeydew and plant exudates) and sodium (in animal matter) for ants among these same habitats. In all habitats, genera that are predominantly carnivorous were comparatively less attracted to NaCl baits than those that rely more on plant matter. These findings lend additional support to the idea that sodium limitation is associated with the ant´s trophic position. At the community level, thus, the attractiveness of sodium sources to ants will depend both on rates of external sodium inputs as well on community composition.

Level of experience modulates individual foraging strategies of an invasive predatory wasp

Spatiotemporal variation in access to resources modulates foraging behavior. Because flexible foraging and subsequent shifting niches can have cascading effects on food webs, it becomes critical to understand what and how information is used during foraging. Yellowjackets are efficient foragers, quickly relocating rewarding resources. Foraging context and the degree of experience were found to affect subsequent behavior and foraging success. An individual forager’s likelihood of relocation was highest for carbohydrates compared to protein and for higher-quality baits. While there was no evidence that odor marking is involved in relocation of sucrose baits, foragers did utilize visual landmarks in the context of protein scavenging. Wasps with limited experience (<4 visits) with a bait responded the most to landmark displacement. However, more experienced wasps avoided misdirection and correctly cued in on the bait. Commensurate with training, a wasp forager visited more often and improved search times at the exact resource location despite displaced landmarks. Successful wasps may detect and associate multiple cues with the training micro-site; such integration of cues could allow the wasps to return to a specific location, even when obvious cues are displaced. Thus, reinforced associative learning likely contributes substantially to foraging patterns and ultimately invasion success, with resource reliability playing a large role. This emphasizes the importance of controlling for experience when comparing foraging across treatments or studies for social wasps.

Control of Rhagoletis indifferens using thiamethoxam and spinosad baits under external fly pressure and its relation to rapidity of kill and residual bait activity

Control of western cherry fruit fly (Rhagoletis indifferens Curran) using thiamethoxam in sucrose bait (sucrose only) and spinosad bait (GF-120, spinosad in a mix of sugar, protein, ammonium acetate, and other ingredients) in cherry orchards with external fly pressure and the residual activity of these baits were studied in Washington state and Utah, U.S.A., in 2010 and 2011. Thiamethoxam baits applied weekly controlled larval infestations better than spinosad bait applied weekly in one of four trials and did not differ from spinosad bait applied weekly in the remaining trials. Thiamethoxam baits applied every two weeks controlled larval infestations better than spinosad bait applied every two weeks in two of three trials, and did not differ statistically from spinosad bait applied weekly. Thiamethoxam bait that was aged on sweet cherry leaves in the field for 0, 7, 14, and 21 days killed flies more rapidly than spinosad bait that was aged for the same periods and reduced oviposition more than spinosad bait in the laboratory. Thiamethoxam bait retained activity up to 21 days of aging whereas spinosad bait lost activity after 14 or 21 days of aging. Results suggest that when there is external fly pressure, the potentiality of thiamethoxam bait to kill mature R. indifferens more rapidly than spinosad bait may not always translate to better fly control. However, when sprays are applied every two weeks, the longer residual activity of thiamethoxam than spinosad bait does appear to translate to better fly control. This study presents thiamethoxam with sucrose as a new option for an effective bait spray against R. indifferens.

Susceptibility of adult mosquitoes to insecticides in aqueous sucrose baits

Mosquitoes characteristically feed on plant-derived carbohydrates and honeydew just after emergence and intermittently during their lives. Development of toxic baits focusing on this carbohydrate-seeking behavior may potentially contribute to localized control. In the present study, ten insecticides were fed to female Culex quinquefasciatus, Anopheles quadrimaculatus, and Aedes taeniorhynchus in a 10% sucrose solution. Active ingredients representative of five classes of insecticides (pyrethroids, phenylpyroles, pyrroles, neonicotinoids, and macrocyclic lactones) were selected for comparison with commercial formulations used to facilitate incorporation of active ingredients into aqueous sucrose solutions. Sucrose as a phagostimulant significantly enhanced mortality to toxicants. In general, the most effective active ingredients were fipronil, deltamethrin and imidacloprid, followed by spinosad, thiamethoxam, bifenthrin, permethrin, and cyfluthrin. The least effective ingredients were chlorfenapyr and ivermectin. For some of the ingredients tested, Cx. quinquefasciatus was the least susceptible species. One-day-old male Cx. quinquefasciatus were more susceptible than females; however, no differences existed between one- and seven-day-old mosquitoes. There were no differences in susceptibility between unfed and gravid ten-day-old female Cx. quinquefasciatus to bifenthrin. In conclusion, several pesticides from different classes of compounds have potential for use in development of toxic baits for mosquitoes.

Mortality and Oviposition of Western Cherry Fruit Fly (Diptera: Tephritidae) Exposed to Different Insecticide Baits for Varying Periods in the Presence and Absence of Food

Spinosad bait is used to control western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), by killing flies before they oviposit. However, effects of different insecticide baits on management of reproductively mature flies are largely unknown. Objectives here were to determine mortality and oviposition of reproductively mature R. indifferens exposed to different insecticide baits for varying periods in the presence and absence of dried yeast extract and sucrose food. Spinosad bait (spinosad in a mix of protein, sugar, and other ingredients) was compared with acetamiprid, thiamethoxam, and imidacloprid in sucrose or Nu-Lure + sucrose bait. When flies were exposed to treatments and then offered cherries, Prunus avium (L.) L., for oviposition or when they were exposed to treatments and cherries simultaneously, both thiamethoxam bait and imidacloprid bait resulted in higher mortality and lower oviposition than spinosad bait and acetamiprid bait. Exposures to thiamethoxam bait and imidacloprid bait for six and 24 h were similarly effective, but 6-h exposures to spinosad bait and acetamiprid bait were less effective than 24-h exposures. There was little difference between sucrose and Nu-Lure + sucrose baits. When food was present, thiamethoxam bait and imidacloprid bait caused greater mortality and lower oviposition than spinosad bait and acetamiprid bait, but when food was absent, patterns were less consistent. Because of its ability to kill flies sooner after it is exposed to flies when food is present or absent, thiamethoxam or imidacloprid in sucrose or Nu-Lure bait may reduce infestations in cherries more than spinosad bait when mature R. indifferens are present in orchards.

Laboratory Evaluation of the Efficacy of Fluorescent Biomarkers for Sugar-Feeding Sand Flies (Diptera: Psychodidae)

The purpose of this study was to evaluate the use of four fluorescent dyes (rhodamine B, uranine O, auramine O, and erythrosin B) and two nonfluorescent dyes (carmoisine and indigotine) incorporated into sugar baits as biomarkers for phlebotomine sand flies. Each dye could be detected in sand flies fed baits with dye for 24 h when examined using bright field microscopy, although there was considerable variability in the marking produced; all sand flies that had ingested rhodamine B-treated sucrose solution were marked clearly. Sand flies that had ingested sucrose solution containing rhodamine B or uranine O at concentrations as low as 10 mg/L were consistently detected under fluorescence microscopy. None of the treatments in this study reduced the longevity of sand flies. All sand flies fed sucrose solution containing rhodamine B or uranine O were marked for at least 14 d, whereas only 20% of sand flies were marked 3 d after feeding on a carmoisine-treated solution. When rhodamine B and uranine O were combined in a single sucrose solution or when the dyes were fed sequentially to sand flies, both dyes could be detected in sand flies using fluorescence microscopy. We propose that rhodamine B- or uranine O-treated sucrose baits could be used in ecological studies or to identify portions of the adult sand fly population that could be targeted with insecticide-treated sugar baits.

Laboratory Evaluation of the Efficacy of Fluorescent Biomarkers for Sugar-Feeding Sand Flies (Diptera: Psychodidae)

The purpose of this study was to evaluate the use of four fluorescent dyes (rhodamine B, uranine O, auramine O, and erythrosin B) and two nonfluorescent dyes (carmoisine and indigotine) incorporated into sugar baits as biomarkers for phlebotomine sand flies. Each dye could be detected in sand flies fed baits with dye for 24 h when examined using bright field microscopy, although there was considerable variability in the marking produced; all sand flies that had ingested rhodamine B-treated sucrose solution were marked clearly. Sand flies that had ingested sucrose solution containing rhodamine B or uranine O at concentrations as low as 10 mg/L were consistently detected under fluorescence microscopy. None of the treatments in this study reduced the longevity of sand flies. All sand flies fed sucrose solution containing rhodamine B or uranine O were marked for at least 14 d, whereas only 20% of sand flies were marked 3 d after feeding on a carmoisine-treated solution. When rhodamine B and uranine O were combined in a single sucrose solution or when the dyes were fed sequentially to sand flies, both dyes could be detected in sand flies using fluorescence microscopy. We propose that rhodamine B- or uranine O-treated sucrose baits could be used in ecological studies or to identify portions of the adult sand fly population that could be targeted with insecticide-treated sugar baits.

Leaf cutter ants (Atta cephalotes) harvest baits offering sodium chloride rewards

Recent studies of attraction to sodium chloride baits suggest that diverse ant species forage for salt. We used experimental presentations of salt baits to test whether leaf cutter ants (Atta cephalotes) are attracted to and harvest salt-treated paper baits that offer no other resources. Atta foragers were most attracted to sucrose baits (positive control), but more foragers touched and cut salt-treated baits than water-treated baits (negative control). Furthermore, the ants removed more paper from the salt baits than from water-treated baits. We conclude that leaf cutter ants expend time and energy to harvest salt in the absence of other rewards. Salt could be harvested for the workers’ consumption, or it could be fed to the fungus gardens in the ants’ nest.

Delayed Toxicity as a Critical Factor in the Efficacy of Aqueous Baits for Controlling Argentine Ants (Hymenoptera: Formicidae)

Boric acid, imidacloprid, and thiamethoxam in sucrose aqueous baits had different delayed toxicities to worker Argentine ants, Linepithema humile (Mayr). The concentrations required to produce an LT50 (time required to produce 50% mortality) within 1-4 d were 3.63-0.55% boric acid, 9.2 x 10(-3) to 7.1 x 10(-4)% imidacloprid, and 3 x 10(-4) to 2 x 10(-5)% thiamethoxam. The three toxicants were not repellent. Other laboratory trials showed that 1% boric acid, 5 x 10(-4) to 5 x 10(-3)% imidacloprid, and 1 x 10(-5) to 1 x 10(-3)% thiamethoxam had delayed toxic effects, whereas 0.5% boric acid and < 5 x 10(-3)% imidacloprid did not. Baits that provided an LT50 between days 1 and 4 were considered to have delayed toxic effects. The utility of aqueous sucrose baits and toxicants soluble in such systems and the negative impact of fast-acting toxicants on trail following, recruitment, trophallaxis, and control of Argentine ants are discussed.

Delayed toxicity as a critical factor in the efficacy of aqueous baits for controlling Argentine ants (Hymenoptera: Formicidae).

Boric acid, imidacloprid, and thiamethoxam in sucrose aqueous baits had different delayed toxicities to worker Argentine ants, Linepithema humile (Mayr). The concentrations required to produce an LT50 (time required to produce 50% mortality) within 1-4 d were 3.63-0.55% boric acid, 9.2 x 10(-3) to 7.1 x 10(-4)% imidacloprid, and 3 x 10(-4) to 2 x 10(-5)% thiamethoxam. The three toxicants were not repellent. Other laboratory trials showed that 1% boric acid, 5 x 10(-4) to 5 x 10(-3)% imidacloprid, and 1 x 10(-5) to 1 x 10(-3)% thiamethoxam had delayed toxic effects, whereas 0.5% boric acid and < 5 x 10(-3)% imidacloprid did not. Baits that provided an LT50 between days 1 and 4 were considered to have delayed toxic effects. The utility of aqueous sucrose baits and toxicants soluble in such systems and the negative impact of fast-acting toxicants on trail following, recruitment, trophallaxis, and control of Argentine ants are discussed.

Preferences for sugars and amino acids and their conditionality in a diverse nectar‐feeding ant community

Summary Feeding preferences of nectarivorous ants for sugars and amino acids were studied in an Australian tropical rain forest using artificial nectar solutions. Fifty‐one ant species were recorded feeding on the solutions. Preferences among carbohydrates were principally concordant between ant species. In paired tests, sucrose was often preferred over fructose, glucose, maltose, melezitose, raffinose and xylose, respectively. Attractiveness of sucrose baits increased with concentration. Many ant species preferred sugar solutions containing mixtures of amino acids over pure sugar solutions. However, preferences among seven pairs of single amino acids in sugar solutions differed substantially between ant species, including several cases where different ant species displayed significant opposite choices. Ant selectivity between solutions was significantly reduced when different ant species co‐occurred on the same bait. Preferences for single amino acids were also reduced when colonies fed extensively on the same compound prior to the experiment for 2 days. Our results indicate that both interspecific variability in gustatory preferences and conditional effects such as competition and colony requirements affect resource selection in multispecies communities. These processes may be crucial in niche partitioning of species‐rich nectarivore assemblages.

Virulence of Different Isolates and Formulations of Beauveria bassiana for House Flies and the Parasitoid Muscidifurax raptor

Abstract Adult house flies (Musca domestica) were susceptible (94-100% mortality) to Beauveria bassiana when conidia of the Hf88 isolate were applied to plywood boards at 107 conidia/cm2; a starch dust formulation was more effective than a liquid suspension. Adult flies were also susceptible (90-99% mortality) to this isolate when they were con fined with treated water (108 conidia/ml) or food (108 conidia/100 mg). House fly larvae were not affected by treatments with up to 108 conidia/cm3 of rearing medium. A 2-year survey of house flies cm from New York dairies indicated that most natural infections of house flies occurred in September and October, although prevalence rates never exceeded 1%. Thirteen single-fly isolates obtained during this survey were compared with the Hf88 isolate for virulence against flies; the 2 most virulent isolates were slightly more virulent for flies than for the fly parasitoid Muscidifurax raptor. Incorporation of conidia into a sucrose bait (108 conidia/100 mg) in cages gave high levels of house fly control (78-100% mortality) 5 days after exposure.

Cyclodiene resistance at the insect GABA receptor/chloride channel complex confers broad cross resistance to convulsants and experimental phenylpyrazole insecticides

This study investigated the pharmacological profile of cyclodiene resistance in Drosophila melanogaster and the mode of action of a phenylpyrazole insecticide, JKU 0422. Toxicological studies were performed with a sucrose bait assay containing the synergist piperonyl butoxide. The Maryland strain of D. melanogaster was resistant to dieldrin, lindane, picrotoxinin, TBPS, p-CN-TBOB, and JKU 0422. In contrast, this strain was susceptible to cypermethrin and the avermectins MK-243, abamectin, and abamectin 8,9-oxide. Neurophysiological studies showed that both TBPS and JKU 0422 reversed the inhibitory action of GABA in central nerve preparations from susceptible D. melanogaster. However, the response to these compounds was attenuated in nerve preparations from the resistant Maryland strain, which indicated that the resistance was expressed at the level of the nerve. Topical toxicity bioassays with JKU 0422 on susceptible (CSMA) and cyclodiene-resistant (LPP) strains of German cockroach revealed a resistance ratio of 553-fold for this compound. These studies demonstrate that cyclodiene resistance in D. melanogaster confers broad cross resistance toward compounds thought to block the GABA-gated chloride channel in a manner similar to the cyclodienes. Moreover, the cross resistance extends to JKU 0422, and resistance to this compound is also present in a strain of cyclodiene-resistant German cockroach. These toxicological results, along with the neurophysiological studies, confirm that JKU 0422 has a mode of action that is similar to the cyclodienes and TBPS. These findings suggest that the introduction and use of new chloride channel antagonists as insecticides should be managed carefully in order to prevent the rapid development of resistance in the field.

Susceptibility of the house fly, Musca domestica (Diptera: Muscidae), to the entomogenous nematodes Steinernema feltiae, S. glaseri (Steinernematidae), and Heterorhabditis heliothidis (Heterorhabditidae).

The infectivity of the nematodes Steinernema feltiae, S. glaseri , and Heterorhabditis heliothidis for the larval, pupal, adult stages of the house fly were evaluated under different habitat conditions. Second- and 3rd-instar larvae and adult flies were highly susceptible to S. feltiae and H. heliothidis when hosts were confined in petri dishes containing nematode-treated filter paper. Larvae were not susceptible to S. glaseri , and pupae within puparia were refractory to infection by all 3 species. When 2nd- and 3rd-instar larvae were exposed to nematodes in rearing medium, S. feltiae caused higher mortality (55–61%) than H. heliothidis (11–26%) at the highest dosage of 5,000 nematodes per host. Both S. feltiae and H. heliothidis were more infective for 3rd-instar larvae (21–29%) than for 2nd-instar larvae (2–6%) at this dosage in poultry manure. When adult flies were offered S. feltiae suspensions in a 5% sucrose bait on cotton balls, mortality ranged from 53 to 67% at dose rates ranging from 1,000 to 100,000 nematodes per milliliter of bait.

Seasonal changes in the response of wood‐ants (Formica lugubris) to sucrose baits

Abstract. 1. The acceptability of sucrose solutions to Formica lugubris Zett. in the field was tested by offering droplets of known concentrations to ants tending aphids.2. A probit model fitted to the data allowed the computation of the Median Effective Concentration (ED50) and its confidence limits.3. In spring and early summer ED50 was about 0.15 M sucrose, but the ED50 rose in 1 week at the end of June from 0.2 M to 0.9 M. The change was simultaneous on pine and birch trees. The ED50 fell gradually to about 0.4 M in early November.4. The increase in ED50 is related to the production of the summer apterae in the aphids tended, Cinara pini (L.) on pines and Symydobius oblongus (von Heyden) on birch. This increases the ‘quality’ of food resource so that low sucrose concentrations can no longer compete for ant attendance.5. The increase in ED50 may limit the attendance of wood‐ants at the nectaries of bracken, Pteridium aquilinum (L.) Kuhn. and at colonies of some other aphid species which are attended only in early summer.