Reproductive strategy of the slave antFormica podzolica relative to raiding efficiency of enslaver species

Summary Formica podzolica serves as host to slave-making ants in North America. We propose thatF. podzolica may respond to slavery by two alternative colony-growth and reproductive strategies depending on the raiding ability of the slavemaker: (1) Rapid colony growth at the expense of producing sexuals to a stage where raiding by unspecialized, facultative slavemakers, capable of exploiting only small colonies, becomes unlikely owing to a strong work force and (2) Early production of sexual offspring at the cost of colony growth to secure some sexual production in an environment with specialized obligate enslavers, capable of raiding large colonies. We tested the strategies by excavating 30 small to moderately large mounds ofF. podzolica and measured reproductive parameters of colonies in relation to mound size, worker number, and worker size. Mound area predicted worker number satisfactorily. Worker number correlated significantly with worker head width and with number of worker and sexual offspring. With a growing work force, the proportion of sexual offspring increased in the total offspring. Two thirds of the colonies producing sexuals emitted single sex, sex being independent of colony size. Some of the large colonies produced both sexes with a strong bias toward either sex. The unweighted population-level sex ratio did not differ from even, being 0.52 (numerical) or 0.54 (biomass). Very large mounds (not excavated) had small workers and highly male-biased sex ratios, probably owing to energy constraints set by central-place foraging. Population-level colony ontogeny data did not fit either one of the suggested strategies, but imply a mixture of the two. We discuss an alternative, still untested raid-independent explanation to the ontogeny pattern.     

Effects of experience on food-searching behavior in the antFormica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussitend to return to and search at a site of a previous food find. The search tactic employed by a forager on its return trip is related to the type of food previously encountered: search is more persistent in response to carbohydrate than to protein food. Using different reinforcement schedules with carbohydrate and protein food rewards, we show that, on a short-term as well as on a long-term basis, the basic pattern of search observed in naive foragers is only slightly modified through foraging experience. Foragers do not increase their search effort or adjust their search pattern when either type of food is systematically renewed on a fixed reward schedule and thus do not seem to be able to learn to assess the food predictability. Collective responses that could compensate for this lack of individual flexibility and increase foraging efficiency at the colony level are discussed.     

Control of the phytopathogen Botrytis cinerea using adipic acid monoethyl ester

The in vitro and in vivo antifungal activity of adipic acid monoethyl ester (AAME) on the necrotrophic pathogen Botrytis cinerea has been studied. This chemical effectively controlled this important phytopathogen, inhibited spore germination and mycelium development at non-phytotoxic concentrations. The effectiveness of AAME treatment is concentration-dependent and influenced by pH. Spore germination in the presence of AAME is stopped at a very early stage, preventing germ tube development. In addition, cytological changes such as retraction of the conidial cytoplasm in the fungus are observed. AAME was also found to act on membrane integrity, affecting permeability without exhibiting lytic activity, as described previously for other antifungal compounds. Polyamine content in the mycelium of B. cinerea was also affected in response to AAME treatment, resulting in putrescine reduction and spermine accumulation similar to a number of antifungal agents. Microscopic observation of treated conidia after inoculation on tomato leaves suggested that inhibited spores are not able to attach to and penetrate the leaf. Finally, AAME completely suppressed the grey mould disease of tomato fruits under controlled inoculation conditions, providing evidence for its efficacy in a biological context and for the potential use of this chemical as an alternative fungicide treatment.     

Evolution of nesting strategies of ants: genetic evidence from different population types of Formica ants

Genetic population structure was studied in two types of populations in the ants Formica exsecta and F. pressilabris: populations consisting of single-nest colonies (monodomy) and populations consisting of multi-nest colonies (polydomy). These characteristics seem to be associated with the number of egg-laying females (gynes) in a nest, mating structure of the population, sex ratio and male size variation. The monodomous populations are characterized by single-gyne nests, the population sex ratio is either I:1 or female-biased, males are mainly large-sized, and there is slight inbreeding in the population. The polydomous populations have multi-gyne nests with gynes related to each other, sex ratio is strongly male-biased, most males are small-sized, and there is slight genetic microdifferentiation within the populations. Diploid males found in a polydomous F. pressilabris population suggest that the population is inbred and isolated. Habitat localization is presented as a plausible explanation for the evolution of the polygynous and polydomous population structure.     

Screening of wild accessions resistant to gray mold (Botrytis cinerea Pers.) in Lycopersicon

Tomato gray mold (Botrytis cinerea Pers.) is a common disease worldwide, and often causes serious production loss by infecting leaves, stems, flowers and fruits. Presently, no resistant cultivars are available. To find new breeding materials for gray mold resistance, assessment for resistance of the leaflet and stem in six tomato cultivars, 44 wild tomato accessions and a Solanum lycopersicoides accession was performed. Although no correlation was observed (r=−0.127^ns) between resistance of the leaflet and the stem, L. peruvianum LA2745, L. hirsutum LA2314 and L. pimpinellifolium LA1246 showed high resistance both in the leaflet and in the stem. Particularly, in the leaves of LA2745, no lesions were observed even more than two weeks after the inoculation with conidia, and F1s between a cultivated tomato and LA2745 also showed high resistance as observed in LA2745. From these results, LA2745 is thought to be a promising material for breeding gray-mold resistant cultivars.     

A shift in colony founding behaviour in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2

Summary. A shift in colony founding behaviour from single queen (haplometrosis) to multiple queens (pleometrosis) was observed locally in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2, which is associated with Macaranga trees in Borneo. In addition, about a quarter of all mature colonies (27 of 95 trees examined) were found to be multiple queen colonies. They arose either directly from pleometrotic founding colonies or secondarily by adoption of additional queens. Using microsatellite markers, we showed that queens in colonies founded through pleometrosis are unrelated and each queen participates in producing worker offspring, albeit with significant skew in a third of the colonies. In mature polygynous colonies, all resident queens contributed to the production of workers and sexual offspring. Relatedness of queens in mature polygynous colonies was not significantly higher than in foundress associations. We hypothesize that increased nest site limitation in this specific interaction trigger the observed shift in colony founding behaviour. Crematogaster msp. 2 inhabits the light demanding pioneer plant species Macaranga pearsonii that is typical for early successional stages of secondary forests. Thus suitable host-plants for colonisation are abundant for only a short time in highly disturbed sites and become increasingly sparse when secondary forest matures.Received 6 September 2004; revised 29 November; accepted 10 December 2004.     

Ability of the antagonistic yeast Cryptococcus albidus to control Botrytis cinerea in strawberry

The yeast Cryptococcus albidus, originally isolated from mature strawberry fruits, was tested for antagonistic activity against Botrytis cinerea, the causal agent of grey mould in strawberries. Conidial germination and germ tube growth of conidia of B. cinerea were inhibited by a cell suspension of the antagonist in aqueous strawberry fruit pulp suspension (1%) after 6 and 24 hours of incubation. Application of a cell suspension (1 × 10⁶ cells/ml) on detached strawberry leaf disks incubated at 10°C reduced incidence and conidiophore density of B. cinerea by 86 and 99%, respectively, but effectiveness was reduced at higher temperatures. Treatments with C. albidus during bloom of strawberries reduced incidence of grey mould on ripe strawberry fruits after harvest by 33, 28 and 21% in three years of field trials. The effectiveness of the yeast was increased when formulation substances (alginate, xanthan and cellulose) were added to the cell suspension.     

Effects of water extracts of a composted manure-straw mixture on the plant pathogen Botrytis cinerea

Manure-straw mixtures were composted and water extracts, made by incubating compost in water for 3 to 18 days, were assessed for antagonistic activity against Botrytis cinerea, using a range of tests. Extracts of all ages inhibited conidial germination on glass slides and reduced mycelial growth on agar. Mixing extracts of all ages with droplets of suspensions of B. cinerea conidia on detached Phaseolus bean leaves suppressed lesion development, but only 3- to 8-day-old extracts had an effect when sprayed onto leaves 2 days before inoculation. Extracts contained a large and varied microbial population of actinomycetes (0.3 to 2.4×10⁵ c.f.u.ml^–1), bacteria (1.5 to 5.6×10¹⁰ c.f.u.ml^–1), filamentous fungi (25.0 to 45.5 c.f.u. ml^–1) and yeasts (26.1 to 62.6 c.f.u.ml^–1). Eight- and 18-day-old extracts lost activity completely on filter sterilization or autoclaving. Weekly sprays of 8-day-old extracts onto lettuce in the glasshouse had no effect on the incidence of grey mould, but significantly reduced its severity and increased marketable yield. The use of compost extracts in biocontrol of plant diseases and their possible mode of action is discussed.M.P. McQuilken and J.M. Whipps are and J.M. Lynch was with the Microbiology and Crop Protection Department, Horticulture Research International, Littlehampton BN17 6LP, UK; J.M. Lynch is now with the School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK.     

Isolation and identification of the principal siderophore of the plant pathogenic fungusBotrytis cinerea

Summary The plant pathogenic hyphomyceteBotrytis cinerea has been shown to produce several trihydroxamate siderophores under conditions of low-iron stress. The total siderophores amounted to approximately 30 mg/l culture filtrate after 5 days of incubation in an asparagine/salt/glucose medium. Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) on a reversed phase indicated that ferrirhodin is the predominant siderophore of this fungus. Chemical characterization of the principal siderophore by fast-atom-bombardment (FAB) mass spectrometry, nuclear magnetic resonance (¹H-NMR,¹³C-NMR) and comparison with a reference revealed the identity with ferrirhodin. NMR studies performed on desferrirhodin (desferrirhodin) in dimethylsulfoxide and water revealed the existence of two conformers in D₂O resulting from acis-trans isomerization of the hydroxamic acid groups. Comparative iron-uptake studies showed the following order of uptake inB. cinerea: ferrichrysin (100%), ferrirubin (57%), ferrirhodin (45%), hexahydroferrirhodin (45%), coprogen 6%. Concentration-dependent uptake of ferrirhodin resulted in saturation kinetics only in the low concentration range of 0–30 M (K _m = 2.5 M,V _max = 80 pmol min^–1 mg(^–1). A non-saturable, linear uptake was observed in the high concentration range of 30–80 M. The low concentration range appears to be the physiologically significant range, where siderophore-mediated iron transport inB. cinerea occurs.     

Breeding system and reproductive skew in a highly polygynous ant population

Factors affecting relatedness among nest members in ant colonies with high queen number are still poorly understood. In order to identify the major determinants of nest kin structure, we conducted a detailed analysis of the breeding system of the ant Formica exsecta. We estimated the number of mature queens by mark-release-recapture in 29 nests and dissected a sub-sample of queens to assess their reproductive status. We also used microsatellites to estimate relatedness within and between all classes of nestmates (queens, their mates, worker brood, queen brood and male brood). Queen number was very high, with an arithmetic mean of 253 per nest. Most queens (90%) were reproductively active, consistent with the genetic analyses revealing that there was only a minimal reproductive skew among nestmate queens. Despite the high queen number and low reproductive skew, almost all classes of individuals were significantly related to each other. Interestingly, the number of resident queens was a poor predictor of kin structure at the nest level, consistent with the observation that new queens are produced in bursts leading to highly fluctuating queen number across years. Queen number also varied tremendously across nests, with estimates ranging from five to several hundred queens. Accordingly, the harmonic mean queen number (40.5) was six times lower than the arithmetic mean. The variation in queen number was the most important factor of the breeding system contributing to a significant relatedness between almost all classes of nestmates despite a high average number of queens per nest. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Received 12 November 2007; revised 4 May 2008; accepted 8 May 2008.     

Life span of queens in the antFormica exsecta

Summary The antFormica exsecta commonly has two types of colonies: either polygynous and polydomous or monogynous and monodomous. The longevity of queens was studied in monogynous colonies in southern Finland by indirect methods using genetic markers; these data were also used to estimate the number of matings and queen replacement. The average genetic relatedness among worker nest mates was 0.72. Taking inbreeding into account (the inbreeding coefficient wasF=0.16), this value agrees with the assumption that 40% of the queens mated with one male and 60% with two males. The distribution of genotypes within colonies remained stable in successive years, indicating that queen replacement did not occur or was extremely rare. This means that the life span of nests reflects directly the life span of the queens. Eleven of the 16 nests found in 1979 were still alive ten years later. This corresponds to an annual mortality of 3.7% and a mean life span of 27 years. A total of 57 colonies were mapped in the population over a period of ten years. Averaging over the years, the annual mortality was estimated to be 4.9%. This represents a mean life span of 20 years if mortality was independent of age.     

Production of laccase byBotrytis cinerea and fermentation studies with strain F226

After induction, seven strains ofBotrytis cinerea released into the culture broth considerable amounts of laccase in a brief production time. The set-up of a suitable production process was studied with a selected strain in a 10-L fermenter. The optimum fermentation conditions were a 3% inoculum with a high degree of sporulation, a simple medium containing 20 g L^–1 of glucose and 2 g L^–1 of yeast extract at pH 3.5, 2 g L^–1 gallic acid as inducer, added after 2 days of growth, an agitation speed of 300 rpm, an aeration rate of 1.2 vvm and a temperature of 24°C. By optimizing the culture conditions, the enzyme activity reached 28 U ml^–1 in 5 days with a specific activity of 560 U mg^–1 protein. The best procedure to obtain a suitable crude enzyme preparation was concentration of the supernatant medium to 10% of the initial volume by ultrafiltration, followed by a fractional precipitation with ethanol. The optimum pH and temperature for laccase activity were 5.5 and 40°C, respectively, with syringaldazine as the substrate.     

Experimental Conversion of Colony Social Organization in Fire Ants (<Emphasis Type="Italic">Solenopsis invicta</Emphasis>): Worker Genotype Manipulation in the Absence of Queen Effects

Colony social organization in the fire ant Solenopsis invicta appears to be under strong genetic control. In the invasive USA range, polygyny (multiple queens per colony) is marked by the presence of the Gp-9 ^b allele in most of a colony’s workers, whereas monogyny (single queen per colony) is associated with the exclusive occurrence of the Gp-9 ^B allele. Ross and Keller, Behav Ecol Sociobiol 51:287–295 (2002) experimentally manipulated social organization by cross-fostering queens into colonies of the alternate form, thereby changing adult worker Gp-9 genotype frequencies over time. Although these authors showed that social behavior switched predictably when the frequency of b-bearing adult workers crossed a threshold of 5–10%, the possibility that queen effects caused the conversions could not be excluded entirely. We addressed this problem by fostering polygyne brood into queenright monogyne colonies. All such treatment colonies switched social organization to become polygyne, coincident with their proportions of b-bearing workers exceeding 12%. Our results support the conclusion that polygyny in S. invicta is induced by a minimum frequency of colony workers carrying the b allele, and further confirm that its expression is independent of queen genotype or history, worker genotypes at genes not linked to Gp-9, and colony genetic diversity.     

Seasonal cycle of colony structure in the Ponerine ant Pachycondyla chinensis in western Japan (Hymenoptera, Formicidae)

Investigation of reproductive strategies of ants in the subfamily Ponerinae is important for understanding of the evolution of social structure and of the significance of caste dimorphisms. The biology of species with mated and egg-laying workers (gamergates) has been studied for many species, however, little attention has been paid to species that reproduce via alate queens only. We investigated the seasonal cycle of changes in the colony structure of Pachycondyla chinensis reproduced by alate queens in western Japan, and found the following novel biological characteristics of this species. P. chinensis showed a remarkable caste dimorphism in ovariole numbers: workers had no ovaries while queens had 18 to 36 ovarioles in their ovaries. The nesting system seemed to be polydomous: 266 of 400 nests collected were queenless. The number of queenless nests increased during the reproductive season. Among the 134 queenright nests, 38 had several mated-queens without significant differences in ovary activation and the remaining 96 nests were monogynous. During winter to early spring, most nests were polygynous. After alate production, most of the old queens seemed to die or be expelled and replaced by new queens. Virgin dealated queens were often found and they seemed to have laid eggs. Received 3 August 2007; revised 19 December 2007; accepted 20 December 2007     

Life history and coldhardiness ofAthrycia cinerea (Dipt.: Tachinidae) in western Canada

Athrycia cinerea Coq. is a univoltine parasitoid of the bertha armyworm,Mamestra configurata Walker (Lepidoptera: Noctuidae), in western Canada. This parasitoid overwinters as a pupa in the soil. These pupae are less sensitive than their host to increased cold stress caused by lower temperatures or danger durations of exposure. Exposure to −7.5°C for 140 days did not significantly reduce survival. Survival decreased with exposure to temperatures from −10 to −20°C, but survival was 48% even after 40 days exposure to −20°C. The frequency distribution ofA. cinerea puparia per host is highly contagious. Other aspects of the life history are described. Contribution No. 1403 Winnipeg Research Station.     

Botrytis cinerea induces the formation of free radicals in fruits ofCapsicum annuum at positions remote from the site of infection

Summary Free radical adducts of the spin trap -(4-pyridyl-1-oxide)-N-tert-butylnitrone have been observed by electron paramagnetic resonance spectroscopy in detached fruits ofCapsicum annuum investigated 5 days after infection withBotrytis cinerea.The spectra of these adducts were at a maximum within the soft rot lesion, but they could also be detected at distances up to 50 mm from the edge of the lesion in samples following main vascular bundles. At distances greater than 40 mm, the spectrum of the ascorbate radical was also seen, and at greater distances from the lesion it was the only radical detected. With samples taken from parenchyma tissue adjacent to the vascular bundles there was little adduct formation and the ascorbate radical could be detected, albeit with reduced intensity compared to healthy tissue, at distances as small as 10 mm from the edge of the lesion. This observation of chemical changes at considerable distances from the infected tissue is in contrast to previous observations on the behaviour of other markers of oxidative stress (e.g., 4-hydroxynonenal, malondialdehyde, single-peak free radical, and Fe(III) (g = 4.27) electron paramagnetic resonance signals), where their levels decreased rapidly outside of the soft rot.     

The grapevine polygalacturonase-inhibiting protein (VvPGIP1) reduces Botrytis cinerea susceptibility in transgenic tobacco and differentially inhibits fungal polygalacturonases

Polygalacturonase-inhibiting proteins (PGIPs) selectively inhibit polygalacturonases (PGs) secreted by invading plant pathogenic fungi. PGIPs display differential inhibition towards PGs from different fungi, also towards different isoforms of PGs originating from a specific pathogen. Recently, a PGIP-encoding gene from Vitis vinifera (Vvpgip1) was isolated and characterised. PGIP purified from grapevine was shown to inhibit crude polygalacturonase extracts from Botrytis cinerea, but this inhibitory activity has not yet been linked conclusively to the activity of the Vvpgip1 gene product. Here we use a transgenic over-expression approach to show that the PGIP encoded by the Vvpgip1 gene is active against PGs of B. cinerea and that over-expression of this gene in transgenic tobacco confers a reduced susceptibility to infection by this pathogen. A calculated reduction in disease susceptibility of 47–69% was observed for a homogeneous group of transgenic lines that was statistically clearly separated from untransformed control plants following infection with Botrytis over a 15-day-period. VvPGIP1 was subsequently purified from transgenic tobacco and used to study the specific inhibition profile of individual PGs from Botrytis and Aspergillus. The heterologously expressed and purified VvPGIP1 selectively inhibited PGs from both A. niger and B.␣cinerea, including BcPG1, a PG from B. cinerea that has previously been shown to be essential for virulence and symptom development. Altogether our data confirm the antifungal nature of the VvPGIP1, and the in vitro inhibition data suggest at least in part, that the VvPGIP1 contributed to the observed reduction in disease symptoms by inhibiting the macerating action of certain Botrytis PGs in planta. The ability to correlate inhibition profiles to individual PGs provides a more comprehensive analysis of PGIPs as antifungal genes with biotechnological potential, and adds to our understanding of the importance of PGIP:PG interactions during disease and symptom development in plants.Dirk A. Joubert and Ana R. Slaughter contributed equally to this work.     

Use of some essential oils as post-harvest botanical fungicides in the management of grey mould of grapes caused by Botrytis cinerea

During screening of twenty six essential oils against Botrytis cinerea, the essential oils of the ten plants viz. Chenopodium ambrosioides, Eucalyptus citriodora, Eupatorium cannabinum, Lawsonia inermis, Ocimum canum, O. gratissimum, O. sanctum, Prunus persica, Zingiber cassumunar and Z. officinale were found to exhibit absolute fungitoxic activity (100% growth inhibition). The essential oils of O. sanctum, P. persica and Z. officinale were selected for further investigation because these oils showed lower Minimum Inhibitory Concentration (MIC) as compared to the other fungitoxic oils. The selected oils were subsequently standardized through physico-chemical and fungitoxic properties. The MIC values of O. sanctum, P. persica and Z. officinale were found to be 200, 100 and 100 ppm (mg/l) respectively. The oils showed fungistatic nature at their respective MIC. The oils were thermostable, and exhibited a wide range of fungitoxicity against 15 other post-harvest fungal pathogens. The oils had the potency to withstand high inoculum density. The antifungal potency of oils was found to be greater in comparison to some prevalent synthetic fungicides. Practical applicability of the essential oils was observed in control of grey mould of grapes caused by B. cinerea during storage. The O. sanctum- and P. persica-oil-treated grapes showed enhancement of storage life up to 5 and 4 days respectively. The storage life of Z. officinale-oil-treated grapes was found to be enhanced up to 6 days. The oils did not exhibit any phytotoxic effect on the fruit peel. Therefore, the oils could be recommended as a potential source of ecofriendly botanical fungicide, after long term and wide ranging trials.