Steroidal glycoalkaloid content of potato,tomato and their somatic hybrids

Summary Analyses of leaves and ‘tubers’ from somatic hybrids of potato and tomato (‘pomato’ with plastids of potato, ‘topato’ with plastids of tomato) produced by fusion of protoplasts from liquid cultures of dihaploid potato and mesophyll of tomato revealed the presence of the two major potato glycoalkaloids (α-solanine and α-chaconine) as well as the tomato glycoalkaloid (αtomatine). The total alkaloid content of leaves was greater than that of ‘tubers’ and similar to levels in the foliage of parent plants. However, glycoalkaloids were more abundant in hybrid ‘tubers’ than in normal potato tubers by a factor of 5–15. In hybrid foliage, approximately 98% of the alkaloid present was of potato origin whereas in ‘tubers’ the reverse was the case, with tomatine comprising 60–70% of the total alkaloid. The similarities in alkaloid content and ratios between the pomato and the topato lines indicate that plastomes do not influence the biosynthesis and distribution of these alkaloids. The results indicate that major secondary metabolites may prove useful for assessing the hybrid nature of such plants.     

How predatory mites find plants with whitefly prey

We investigated the searching behaviour of two species of predatory mites, Typhlodromips swirskii (Athias-Henriot) and Euseius scutalis (Athias-Henriot), both known to feed on immature stages of the whitefly Bemisia tabaci Gennadius. When released in a greenhouse inside a circle of cucumber plants that were alternatingly clean or infested with immature whiteflies, the mites took several days to find plants. Both species were recaptured significantly more on plants with whiteflies. This suggests that the mites are able to discriminate between plants with and without whiteflies. The predators may either have been attracted to plants with whiteflies from a distance or arrested on plants with whiteflies. Typhlodromips swirskii that had previously fed on whitefly immatures on cucumber leaves were significantly attracted by volatiles from cucumber plants with whiteflies in a Y-tube olfactometer. This suggests that the mites use volatile cues to discriminate between infested and clean plants. However, this response waned rapidly; if predators, experienced as above, were starved for 3–4 h in absence of cucumber leaves, they no longer preferred volatiles of infested plants to clean plants. Furthermore, T. swirskii that had no experience with immature whiteflies on cucumber plants also did not prefer odours of infested plants to those of clean plants. Because the release experiment with this species in the greenhouse was done with inexperienced predators, this suggests that the aggregation of mites on plants with whiteflies was mainly caused by differential arrestment of mites on plants with prey and clean plants. For T. swirskii, this was in agreement with the finding that the fraction of predators on plants with prey increased with time to levels higher than 70%. A less clear trend was found for E. scutalis, for which the fraction of predators on plants with prey stabilized soon after release to levels from 54–70%. Hence, the predatory mites may find plants with prey by random searching, but they are subsequently arrested on these plants. An earlier study showed that 87% of all whiteflies released in a set-up as used here were recaptured within 1 day. Hence, the effectiveness with which predatory mites locate plants with whiteflies is low compared with that of their prey. We expect this to generate spatial patterns in the dynamics of predator and prey and this may have consequences for biological control of whiteflies with predatory mites.     

Tomato-aphid-hoverfly: a tritrophic interaction incompatible for pest management

Trichome-based tomato resistance offers the potential to reduce pesticide use, but its compatibility with biological control remains poorly understood. We evaluated Episyrphus balteatus De Geer (Diptera, Syrphidae), an efficient aphidophagous predator, as a potential biological control agent of Myzus persicae Sulzer (Hemiptera, Aphididae) on trichome-bearing tomato cultivars. Episyrphus balteatus’ foraging and oviposition behavior, as well as larval mobility and aphid accessibility, were compared between two tomato cultivars (Lycopersicon esculentum Mill. ‘Moneymaker’ and ‘Roma’) and two other crop plants; broad bean (Vicia faba L.) and potato (Solanum tuberosum L.). Hoverfly adults landed and laid more eggs on broad beans than on three species of Solanaceae. Hoverfly larval movement was drastically reduced on tomato, and a high proportion of hoverfly larvae fell from the plant before reaching aphid prey. After quantifying trichome abundance on each of these four plants, we suggest that proprieties of the plant surface, specifically trichomes, are a key factor contributing to reduced efficacy of E. balteatus as a biological agent for aphid control on tomatoes. Handling editor: Stanislaw Gorb     

Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.     

Life history ofAphis gossypii on cucumber: influence of temperature, host plant and parasitism

Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2 days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9 and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25°C (r _m =0.556 day⁻¹). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀ on leaves of the lower, middle and upper leaf layer, respectively). Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to the longevity of aphids not stung byA. colemani.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

How species-specific is the phoretic relationship between the broad mite, Polyphagotarsonemus latus (Acari: Tarsonemidae), and its insect hosts?

Broad mite, Polyphagotarsonemus latus (Acari: Tarsonemidae), is a serious plant pest in tropical and subtropical regions. Phoretic associations between broad mite and two genera of whiteflies (Insecta: Homoptera: Aleyrodidae), namely Bemisia and Trialeurodes, have been reported from different parts of the world. Our purpose was to determine the specificity of the association between the mite and its phoretic hosts. Two host plants, potatoes and cucumbers, were used to study these relationships in the laboratory. Insects frozen for 24h were used as potential phoretic hosts in all experiments. Attachment levels were monitored by counting the number of mites attached to each insect. All tests were conducted for 4–6h, as attachment to Bemisia tabaci on potato shoots leveled off after 4h, increasing only marginally after 8h. Attachment levels to thrips (the western flower thrips, Frankliniella occidentalis) and to allate aphids (Myzus persicae) was negligible relative to the attachment to B. tabaci. Broad mite also attached to the whiteflies Dialeurodes citri, Aleyrodes singularis and Trialeurodes lauri, the latter being the least attractive species (including B. tabaci). Washing B. tabaci with pentane greatly reduced attachment. Using cucumbers as hosts did not substantially change the general trend, but attachment levels were lower. The phoretic relationship between broad mite and its insect hosts appears to be specific to whiteflies, with some whiteflies having a higher potential as phoretic hosts.     

Transfers ofVarroa mites from newly emerged bees: Preferences for age- and function-specific adult bees (Hymenoptera: Apidae)

Movements of the parasitic honey bee mite,Varroa jacobsoni (Oud.) were monitored in several assays as they moved among adult host honey bees,Apis mellifera. We examined the propensity of mites to leave their hosts and to move onto new bee hosts. We also examined their preference for bees of different age and hive function. Mites were standardized by selecting mites from newly emerged worker bees (NEWs). In closed jars, 50% ofVarroa left NEWs irreversibly when no physical path was present for the mites to return to the NEWs; about 90% of mites left newly emerged drones in identical assays. In petri dish arenas, mites were rarely seen off NEW hosts when monitored at 15-min intervals for 4 h; this was the case for single NEWs with one mite (NEWs+) and when a NEW+ and a NEW− (no mites) were placed together in a petri dish. When a NEW+ was held with either a nurse beeor a pollen forager, 25% of the mites moved to the older bees. When both a nurseand a pollen forager were placed in a petri dish with a NEW+, about 50% of the mites transferred to older bees; nurse bees received about 80% of these mites, whereas pollen foragers received significantly fewer mites (about 20%,P < 0.05). Most mite transfers occurred during the first 30 min after combining NEWs+ and test bees. When NEWs+ were combined with bees of known ages, rather than function, mites transferred more often to young bees than to older bees (1- and 5-day-old bees vs. 25-day-old bees,P < 0.05; 1-day-old vs. 13- and 25-day-old bees;P < 0.05). No differences in proportions of transferring mites were seen when the range of bee ages was ≤ 8 days (P > 0.05), implying that the factors mediating the mites’ adult-host preference change gradually with bee age. A possible chemical basis for host choice byVarroa is indicated by their greater propensity to move onto freezer-killed nurse bees than onto freezer-killed pollen foragers (P < 0.05) and by their lower movement onto heat-treated bees than onto control bees (P < 0.05). Bee age, hive function, and directional changes in cuticular chemistry are all correlated. Movements of newly emerged mites in relation to these variables may provide insights into their reproductive success inApis mellifera colonies.     

Factors affecting the distribution of a predatory mite on greenhouse sweet pepper

The predatory mite Neoseiulus cucumeris is used for biological control of phytophagous mites and thrips on greenhouse cucumber and sweet pepper. In a previous study, N. cucumeris provided effective control of broad mite but was only rarely found on the sampled leaves, raising questions about the factors affecting N. cucumeris distribution. To determine the distribution of N. cucumeris, leaves of pepper plants were sampled three times per day: just after sunrise, at noon and just before sunset for two years and throughout a 24 h period in one year. The presence of other mites and insects was recorded. Biotic (pollen) and abiotic (temperature, humidity) factors were monitored from the three plant levels. The effect of direct and indirect sunlight on the mites was assessed. N. cucumeris was found primarily in flowers; however, the mite’s distribution was affected by other predators (intraguild predation); in the presence of the predatory bug Orius laevigatus virtually no mites occurred in the flowers. Whereas temperature and humidity varied from the top to the lower level of the plants, apparently neither these factors nor the presence of pollen outside the flowers influenced mite distribution. N. cucumeris was found to be negatively phototropic; therefore N. cucumeris were pre-conditioned to light by rearing under light conditions for 4 months before being released. The light-reared mites were initially more numerous during the noon sampling period, however, rearing conditions caused only a temporary and non-significant change in distribution.     

Rust mite resistance in apple assessed by quantitative trait loci analysis

The aim of this study was to assess the genetic basis of rust mite (Aculus schlechtendali) resistance in apple (Malus × domestica). A. schlechtendali infestation of apple trees has increased as a consequence of reduced side effects of modern fungicides on rust mites. An analysis of quantitative trait loci (QTLs) was carried out using linkage map data available for F₁ progeny plants of the cultivars ‘Fiesta’ × ‘Discovery’. Apple trees representing 160 different genotypes were surveyed for rust mite infestation, each at three different sites in two consecutive years. The distribution of rust mites on the individual apple genotypes was aggregated and significantly affected by apple genotype and site. We identified two QTLs for A. schlechtendali resistance on linkage group 7 of ‘Fiesta’. The AFLP marker E35M42-0146 (20.2 cM) and the RAPD marker AE10-400 (45.8 cM) were closest positioned to the QTLs and explained between 11.0% and 16.6% of the phenotypic variability. Additionally, putative QTLs on the ‘Discovery’ chromosomes 4, 5 and 8 were detected. The SSR marker Hi03a10 identified to be associated to one of the QTLs (AFLP marker E35M42-0146) was traced back in the ‘Fiesta’ pedigree to the apple cultivar ‘Wagener’. This marker may facilitate the breeding of resistant apple cultivars by marker assisted selection. Furthermore, the genetic background of rust mite resistance in existing cultivars can be evaluated by testing them for the identified SSR marker. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of leguminous ground cover competition on red birch and soil nutrient status in the nursery

Legumes as ground cover are regularly planted to increase nitrogen economy of crops and to improve soil. In the present study various clover species were evaluated as vegetative ground cover in nursery field production of micropropagated red birch (Betula pubescensEhrh. f. rubraUlvinen f. nova) in two 2-year experiments. The clover species and cultivars, Trifolium pratenseL. ‘Bjursele’, T. repens L. ‘Jogeva’, T. repens L. ‘Sonja’, T. hybridum L. ‘Frida’, T. incarnatum L. ‘Opolska’, T. resupinatum L. and T. subterraneum L. were compared to grass sod Festuca rubra L. ‘Ensylva’ and to a coverless ground (control). The last one was kept weed free by hand hoeing. Birch (leaves, stems, branches and roots) and soil nutrient concentrations (N, P, K, Ca, Mg and Fe) were analysed and nutrient ratios in birch determined. The annual clovers, T. incarnatumL., T. resupinatumL. and T. subterraneumL., provided about the same nutrient status in birch as did the control. Perennial clovers and grass were strong competitors with trees. High levels of P and Mg in birch leaves relative to N concentration were typical for poorly growing seedlings. Neither annual nor perennial clovers did generally improve soil nutrient status. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inheritance of resistance to the two-spotted spider mite from L. pimpinellifolium (Jusl.) Mill. accession ‘TO-937’

The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of tomato (Lycopersicon esculentum Mill.) crops in temperate regions as this spider mite has a very large capacity for population increase and causes severe tomato yield losses. There is no described tomato cultivar fully resistant to this pest, although resistant accessions have been reported within the green-fruited tomato wild species L. pennellii (Corr.) D’Arcy and L. hirsutum Humb. & Bonpl. We observed a L. pimpinellifolium (Jusl.) Mill. accession, ‘TO-937’, which seemed to be completely resistant to mite attacks and we crossed it with the susceptible L. esculentum cultivar. ‘Moneymaker’ to obtain a family of generations consisting of the two parents, the F₁, the F₂, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium. This family was evaluated for mite resistance in a polyethylene greenhouse using an experimental design in 60 small complete blocks distributed along 12 double rows. Each block consisted of five F₂ plants in one row and one plant of each of the two parents, the F₁, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium in the adjacent row. Plants at the 10–15 leaf stage were artificially infested by putting on them two pieces of French bean leaf heavily infested with T. urticae. After two months, evaluations of infestation were made by visual observation of mite nets and leaf damage. Plants that were free of signs of mite reproduction on the top half were considered as resistant, plants with silky nets only on their basal leaves, intermediate, and plants with mite reproduction on both basal and top canopies were scored as susceptible. Dominance for resistance appeared because all the ‘To-937’, BC₁ to L. pimpinellifolium, and F₁ plants were resistant. Not all ‘Moneymaker’ plants behaved as susceptible because 35% of plants were intermediate. In the BC₁ to L. pimpinellifolium and the F₂, most plants were scored as resistant, only 7 % BC₁ and 3 % F₂ plants were intermediate, and a single F₂ plant (0.3 %) was susceptible. With these figures, resistance seemed to be controlled by either four or two genes according to whether segregation in the BC₁ or in the F₂, respectively, were considered. These results could in part be explained because of appearance of negative interplot interference due to the high frequency of resistant genotypes within most of the generations. Therefore, the family was evaluated again but using a different experimental design. In the new experiment, 16 ‘TO-937’, 17 ‘Moneymaker’, 17 F₁, 37 BC₁ to L. pimpinellifolium, 38 BC₁ to L. esculentum, and 125 F₂ plants were included. Each of these test plants was grown besides a susceptible ‘Moneymaker’ auxilliary plant that served to keep mite population high and homogeneous in the greenhouse. Negative interplot interference was avoided with this design and all the ‘TO-937’, F₁, and BC₁ to L. pimpinellifolium plants were resistant, all ‘Moneymaker’ test plants were susceptible, and 52 % BC₁ to L. esculentum and 25 % F₂ plants were susceptible, which fitted very well with the expected for resistance governed by a single dominant gene. The simple inheritance mode found will favour sucessful introgression of mite resistance into commercial tomatoes from the very close relative L. pimpinellifolium.     

Expression of hepatitis B surface antigen in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> utilizing glyceraldeyhyde-3-phosphate dehydrogenase promoter of <Emphasis Type="Italic">Pichia pastoris</Emphasis>

An expression vector constructed from genes of Pichia pastoris was applied for heterologous gene expression in Saccharomyces cerevisiae. Recombinant hepatitis B surface antigen was synthesized by cloning hepatitis B virus ‘S’ gene under the control of glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter of Pichia pastoris in Saccharomyces cerevisiae. Hepatitis B surface antigen was constitutively expressed, was stable and exhibited ∼20–22 nm particle formation. Stability and absence of toxicity to the host with the expression vector indicates the expression system can be applied for large-scale production.     

Response of antioxidant activity to excess copper in two cultivars of <Emphasis Type="Italic">Brassica campestris</Emphasis> ssp. <Emphasis Type="Italic">chinensis</Emphasis> Makino

Changes in ascorbic acid content and antioxidant enzyme activities were investigated in non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) leaves of ‘Wutacai’ and ‘Erqing’ exposed to excess copper (Cu). Cu treatment reduced the fresh weight of shoot and root by 57% and 46% in ‘Wutacai’, and 60 and 54% in ‘Erqing’, respectively. The accumulation of copper in leaves was higher in ‘Wutacai’ than that in ‘Erqing’. Compared to the control, ascorbic acid (AsA) contents were significantly decreased after copper treatment in both cultivars, while they were higher in ‘Wutacai’ than in ‘Erqing’, which may explain the higher copper-tolerance of ‘Wutacai’ with higher copper accumulation. The higher AsA contents of ‘Wutacai’ resulted from their lower activities of degrading enzymes, such as ascorbate oxydase (AAO) and ascorbate peroxidase (APX), as well as the increasing activity of dehydroascorbate reductase (DHAR) after copper treatment compared with ‘Erqing’. Copper stimulated superoxide dismutase (SOD) activity in both cultivars, but for catalase (CAT), there was little difference between both cultivars. Peroxidases (POD) activity was decreased after copper treatment in ‘Erqing’, while in ‘Wutacai’, it was significantly increased at 14 days, and POD activity was higher in ‘Wutacai’ than that in ‘Erqing’ at 21 and 28 days. Therefore, the induced increasing activity of POD in ‘Wutacai’ also played an important role in its copper tolerance.     

The influence of host fruit morphology on parasitization rates in the Caribbean fruit fly,Anastrepha suspensa

Among the host fruits of the Caribbean fruit fly there are a variety of sizes and shapes. These morphological differences may influence the vulnerability of the larvae to parasites. In the laboratory, Caribbean fruit fly larvae placed in the smaller of 2 different sizes of artificial ‘fruit’ (cloth spheres filled with a diet material) were parasitized at a higher rate by the braconid,Diachasmimorpha longicaudata (Ashmead) when spheres were presented separately. However, when parasites were simultaneously presented with 6 different sizes of ‘fruit’ there was no significant relationship between size and parasitization rate. This may be due to the parasites preference to search for larvae in larger ‘fruit’. In field collections of different species of host fruit, a significant inverse correlation exists between fruit radius and rate of parasitization. However, host fruit size accounts for only about 5% of the variance in yearly parasitization rates.      

Patterns of host ant use by sympatric populations of <Emphasis Type="Italic">Maculinea alcon</Emphasis> and <Emphasis Type="Italic">M. ‘rebeli’</Emphasis> in the Carpathian Basin

Maculinea butterflies show social parasitism via obligatory myrmecophily as their larvae are adopted and raised to pupation by Myrmica ants. Suitable hosts differ for different Maculinea species, and host ant specificity can further differ at the population-level. Although early studies suggested single ant species as main hosts for each Maculinea species, it has recently become clear that their host ant specificity is more complex. Maculinea alcon and Maculinea ‘rebeli’ have variously been separated according to adult and larval morphology, phenology, and their use of different ecosystems, including host plant and host ant species. However, recent genetic evidence has questioned their separation as good species. Here we compare the use of host ants by M. alcon and M. ‘rebeli’ at the regional scale in NE-Hungary and Transylvania (Romania), where molecular studies have found no species-level separation between the two forms. We opened 778 nests of Myrmica ants and searched for Maculinea specimens (larvae, pupae and exuviae) shortly before imago emergence from the nest in seven M. alcon sites, six M. ‘rebeli’- sites and one site where both M. alcon and M. ‘rebeli’ are syntopic. In all, Maculinea caterpillars were found in the nests of seven different ant species (M. alcon was recorded mainly with Myrmica scabrinodis and occasionally with M. salina and M. vandeli; M. ‘rebeli’ used mainly M. scabrinodis, M. sabuleti and M. schencki and occasionally M. lonae and M. specioides). Myrmica scabrinodis was found to be a general host of both M. alcon and M. ‘rebeli’, which is the first record for a common host ant of these two closely related butterflies within the same region. However there were also differences in host ant use patterns between the sites occupied by the two Maculinea taxa, which reflect differences in Myrmica communities between the two types of habitat. Possible explanations for the similar but not identical host use patterns of M. alcon and M. ‘rebeli’, and their relevance for the question of whether they are separate species are discussed. Received 27 November 2007; revised 28 May 2008; accepted 11 June 2008.     

Potential role of parasitism in the evolution of mutualism in astigmatid mites: Hemisarcoptes cooremani as a model

Phoresy is a symbiotic interaction that results in dispersal, benefiting the relocated organism without negatively impacting the phoretic host. It has long been considered that phoresy among astigmatid mites is somehow an intermediate precursor to the evolution of parasitism within the group. In astigmatid mites, only the heteromorphic deutonymph (hypopode) participates in phoretic dispersal, and the plesiomorphic hypopode may be the key to understanding the dynamics of the evolution of that parasitism. Hypopodes of Hemisarcoptes cooremani (Acari: Acariformes) and their phoretic beetle host Chilocorus cacti (Coleoptera: Coccinellidae) have become the experimental focus for studies concerned with the potential forces that influence the transition of a free-living life style into various coevolved relationships. Previous radiolabeling studies applied to H. cooremani and C. cacti determined that hypopodes of H. cooremani acquired resources from adults of C. cacti while in transit, negating the paradigm that the heteromorphy was purely phoretic. To further probe this relationship, we tested whether materials could be passed from the mites to their hosts. We report here a study using a tritium radiolabel, which indicated that beetles also acquire resources from the hypopodes. These results have implications for understanding the complex relationship between H. cooremani and C. cacti. We propose that this relationship should now correctly be defined as mutualistic (not phoretic) and develop a general model for the potential role of parasitism in the evolution of mutualism among the Astigmata.