Fitness costs in clothianidin-resistant population of the melon aphid, Aphis gossypii

Clothianidin is a second-generation neonicotinoid insecticide, widely used against sap-sucking insect pest including melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae). This pest causes severe economic damage to Cucurbitaceae plants worldwide. In this study, we investigated clothianidin resistance development under continuous selection pressure. Moreover, the age-stage, two-sex life table approach was used to evaluate the impact of clothianidin resistance on the fitness of A. gossypii. A clothianidin resistant strain (CT-R) with a 23.17-fold resistance level was developed from a susceptible strain (CT-S) after continuous selection for 24 generations. Life table results showed a significant reduction in the relative fitness (0.847) of CT-R strain compared to the CT-S strain of A. gossypii. The developmental duration, oviposition days, total pre-oviposition period (TPOP), longevity, and fecundity of CT-R strain were found to be significantly lower when compared to CT-S strain. The demographic parameters, including the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0), and mean generation time (T) were also significantly decreased in CT-R strain compared to the CT-S strain. Both the reproductive and survival rates were affected by clothianidin resistance in CT-R strain compared with the CT-S strain of A. gossypii. Overall, our results demonstrate that in-depth knowledge about the trade-off at play between resistance degree and fitness cost might be useful to design resistance management strategies against A. gossypii.

Elevated CO2 concentration affects the defense of tobacco and melon against lepidopteran larvae through the jasmonic acid signaling pathway

The massive use of fossil fuels since the industrial revolution has led to a rapid increase in the concentration of carbon dioxide (CO2) in the atmosphere. What effects elevated CO2 concentrations (ECO2) have on the defense mechanisms plants employ against insects remains poorly understood. This study showed that ECO2 of 750 ± 20 mmol/mol, increased the photosynthetic rate and biomass gain of tobacco and melon plants. However, while mass gain of Spodoptera litura, a nocturnal moth in the Noctuidae family, was higher when feeding on tobacco plants under ECO2, mass gain of Diaphania indica was reduced when feeding on melon plant at ECO2 compared to ambient CO2. Plants have many mechanisms to defend themselves against insects. Jasmonic acid (JA) is a crucial element of plant defense against lepidopteran insects. Our study showed that JA levels increased in tobacco plants under ECO2 but decreased in melon plants. It is speculated that ECO2 changes plant resistance to insects mainly by affecting the JA signaling pathway. Nutrient analysis suggested defensive metabolites rather than changes in the total nitrogen or protein content of the plants led to the changes in plant defense levels under ECO2. In summary, ECO2 affects the interaction between plants and insects. The results may provide a theoretical basis for studying the changes in crop resistance to pests under ECO2 and predicting the impact of ECO2 on future agro-ecosystems.

Cucumis metuliferus reduces Meloidogyne incognita virulence against the Mi1.2 resistance gene in a tomato-melon rotation sequence

BACKGROUND

Susceptible tomato cv. Durinta, ungrafted or grafted onto cv. Aligator resistant rootstock, both followed by the susceptible melon cv. Paloma, ungrafted or grafted onto Cucumis metuliferus BGV11135, and in the reverse order, were cultivated from 2015 to 2017 in the same plots in a plastic greenhouse, infested or not with Meloidogyne incognita. For each crop, soil nematode densities, galling index, number of eggs per plant and crop yield were determined. Virulence selection was evaluated in pot experiments.

RESULTS

In the tomato-melon rotation, nematode densities increased progressively for the grafted tomato, being higher than for ungrafted plants at the end of the study; this was not the case in the melon-tomato rotation. Grafted crops yielded more than ungrafted crops in the infested plots. Virulence against the Mi1.2 gene was detected, but not against C. metuliferus. Reproduction of M. incognita on the resistant tomato was ∼ 120% that on the susceptible cultivar after the first grafted tomato crop, but this decreased to just 25% at the end of the experiment.

CONCLUSION

Alternating different resistant plant species suppresses nematode population growth rate and yield losses. Although this strategy does not prevent virulence selection, the level was reduced. © 2018 Society of Chemical Industry.

Plant Growth Promotion and Biocontrol of Pythium ultimum by Saline Tolerant Trichoderma Isolates under Salinity Stress

This present study evaluates three isolates of Trichoderma as plant growth promoting or biological control agents: Trichoderma aggressivum f. sp. europaeum, Trichoderma saturnisporum, and the marine isolate obtained from Posidonia oceanica, Trichoderma longibrachiatum. The purpose is to contribute to an overall reduction in pesticide residues in the fruit and the environment and to a decrease in chemical fertilizers, the excess of which aggravates one of the most serious abiotic stresses, salinity. The tolerance of the different isolates to increasing concentrations of sodium chloride was evaluated in vitro, as well as their antagonistic capacity against Pythium ultimum. The plant growth promoting capacity and effects of Trichoderma strains on the severity of P. ultimum on melon seedlings under saline conditions were also analysed. The results reveal that the three isolates of Trichoderma, regardless of their origin, alleviate the stress produced by salinity, resulting in larger plants with an air-dry weight percentage above 80% in saline stress conditions for T. longibrachiatum, or an increase in root-dry weight close to 50% when T. aggressivum f. sp. europaeum was applied. Likewise, the three isolates showed antagonistic activity against P. ultimum, reducing the incidence of the disease, with the highest response found for T. longibrachiatum. Biological control of P. ultimum by T. aggressivum f. sp. europaeum and T. saturnisporum is reported for the first time, reducing disease severity by 62.96% and 51.85%, respectively. This is the first description of T. aggressivum f. sp. europaeum as a biological control agent and growth promoter. The application of these isolates can be of enormous benefit to horticultural crops, in both seedbeds and greenhouses.

Sustainable alternatives to 1,3-dichloropropene for controlling root-knot nematodes and fungal pathogens in melon crops in Mediterranean soils: Efficacy and effects on soil quality

The control of agricultural pests is key to maintain economically viable crops. Increasing environmental awareness, however, is leading to more restrictive European policies regulating the use of certain pesticides due to their impact on human health and the soil system. Given this context, we evaluated the efficacy of three alternatives to the soil fumigant 1,3-dichloropropene (1,3-D), which is currently banned in Europe: two non-fumigant nematicides [oxamyl (OX) and fenamiphos (FEN)] and the soil fumigant dimethyl disulfide (DMDS). We analysed the efficiency of these pesticides against root-knot nematodes and soil fungal pathogens (determined by qPCR) as well as the soil biological quality after treatments application (estimated by enzyme activities). Among treatments, 1,3-D and DMDS significantly reduced nematode populations. FEN was more effective in sandy soil, while OX had no effect in any soil. OX and FEN had no effect on fungal pathogens, whereas DMDS reduced the abundance of Rhizoctonia solani and Fusarium solani at the root level in clay-loam soil. Soil quality decreased after treatment application but then recovered throughout the experiment, indicating the possible dissipation of the pesticides. Our findings support DMDS as a potential sustainable alternative for controlling root-knot nematodes and fungal pathogens due to its effectiveness in both studied soils, although its negative impact on soil biological quality in sandier soils must be taken into account. Main finding of the work. DMDS is a reliable alternative to 1,3-D for controlling agricultural pest but its inhibitory effect on soil enzyme activities varied according to the soil characteristics.

Impact of the secondary plant metabolite Cucurbitacin B on the demographical traits of the melon aphid, Aphis gossypii

Cucurbitacin B is a natural triterpene present in plants of Cucurbitaceae family, which are among the host plants for melon aphid, Aphis gossypii. In present study we characterized the effects of two cucurbitacin B concentrations on the biological parameters of adults (F0) and of juveniles and adults of their progeny (F1). The results showed that cucurbitacin B at 25 ppm significantly reduced the adult longevity and fecundity of both F0 and F1 generation. Exposure of F0 generation to 25 ppm though reduced the demographic traits of F1 including the intrinsic rate of increase r (day-1), generation time T (day), finite rate of increase λ (day-1), however, only net reproductive rate R0 (offspring/individual) decreased significantly. While 100 ppm reduced not only the longevity and fecundity of F0 generation but also the longevity of F1 generation. Fecundity of F1 was not affected by 100 ppm of cucurbitacin B, however, R0 (offspring/individual) and T (day) of F1 generation were lower than the control population. These results support the hypothesis that high contents of cucurbitacin B caused negative impact on melon aphid and could be used as a lead for classical selection of resistant varieties of plants that are main hosts for the melon aphid.

Using Next-Generation Sequencing to Develop Molecular Diagnostics for Pseudoperonospora cubensis, the Cucurbit Downy Mildew Pathogen

Advances in next-generation sequencing (NGS) allow for rapid development of genomics resources needed to generate molecular diagnostics assays for infectious agents. NGS approaches are particularly helpful for organisms that cannot be cultured, such as the downy mildew pathogens, a group of biotrophic obligate oomycetes that infect crops of economic importance. Unlike most downy mildew pathogens that are highly host-specific, Pseudoperonospora cubensis causes disease on a broad range of crops belonging to the family Cucurbitaceae. In this study, we identified candidate diagnostic markers for P. cubensis by comparing NGS data from a diverse panel of P. cubensis and P. humuli isolates, two very closely related oomycete species. P. cubensis isolates from diverse hosts and geographical regions in the United States were selected for sequencing to ensure that candidates were conserved in P. cubensis isolates infecting different cucurbit hosts. Genomic regions unique to and conserved in P. cubensis isolates were identified through bioinformatics. These candidate regions were then validated using PCR against a larger collection of isolates from P. cubensis, P. humuli, and other oomycetes. Overall seven diagnostic markers were found to be specific to P. cubensis. These markers could be used for pathogen diagnostics on infected tissue, or adapted for monitoring airborne inoculum with real-time PCR and spore traps.

NBS-LRR-mediated resistance triggered by aphids: viruses do not adapt; aphids adapt via different mechanisms

BACKGROUND

Aphids are serious pest on crops. By probing with their stylets, they interact with the plant, they vector viruses and when they reach the phloem they start a continuous ingestion. Many plant resistances to aphids have been identified, several have been deployed. However, some resistances breaking down have been observed. In the melon, a gene that confers resistance to aphids has been deployed in some melon-producing areas, and aphid colony development on Vat-carrying plants has been observed in certain agrosystems. The Vat gene is a NBS-LRR gene that confers resistance to the aphid species Aphis gossypii and exhibits the unusual characteristic of also conferring resistance to non-persistently transmitted viruses when they are inoculated by the aphid. Thus, we characterized patterns of resistance to aphid and virus using the aphid diversity and we investigated the mechanisms by which aphids and viruses may adapt to the Vat gene.

RESULTS

Using a Vat-transgenic line built in a susceptible background, we described the Vat- spectrum of resistance to aphids, and resistance to viruses triggered by aphids using a set of six A. gossypii biotypes. Discrepancies between both resistance phenotypes revealed that aphid adaptation to Vat-mediated resistance does not occur only via avirulence factor alterations but also via adaptation to elicited defenses. In experiments conducted with three virus species serially inoculated by aphids from and to Vat plants, the viruses did not evolve to circumvent Vat-mediated resistance. We confirmed discrepancies between both resistance phenotypes by testing each aphid biotype with a set of thirteen melon accessions chosen to reflect the natural diversity of the melon. Inheritance studies revealed that patterns of resistance to virus triggered by aphids are controlled by different alleles at the Vat locus and at least another locus located at a short genetic distance. Therefore, resistance to viruses triggered by aphids is controlled by a gene cluster.

CONCLUSIONS

Under the Flor model, changes in the avirulence gene determine the ability of the pathogen to overcome the resistance conferred by a plant gene. The Vat gene belongs to a resistance gene family that fits this pest/pathogen-plant interaction, and we revealed an additional mechanism of aphid adaptation that potentially exists in other interactions between plants and pests or pathogens.

Implementing a spinosad-based local bait station to control Bactrocera cucurbitae (Diptera: Tephritidae) in high rainfall areas of Reunion Island

Three species of fruit flies cause serious damage to cucurbit crops on Reunion Island: Bactrocera cucurbitae (Diptera: Tephritidae) (Coquillett 1899), Dacus ciliatus (Loew 1901), and Dacus demmerezi (Bezzi 1917). To control them, a program of agroecological management of cucurbit flies has been implemented based on the application of Synéis-appât, especially spot sprays on corn borders. However, the high rainfall on Reunion Island limits the long-term efficiency of the bait; in addition, this method cannot be used for large chayote trellises, because corn borders cannot be planted around them. The aim of this study was to design a bait station adapted to prevailing conditions on Reunion Island. An 'umbrella trap' tested in Taiwan was used as a reference to compare its efficacy with our local bait station. Experiments were conducted in field cages on B. cucurbitae to test different characteristics of bait stations and to construct one using local materials. Results were validated in the field. The attractiveness of the bait station was related mainly to the color of the external surface, yellow being the most attractive color. The efficacy of the bait station with respect to fly mortality was found to be linked to the accessibility of the bait, and direct application of Synéis-appât on the bait station was found to be the most efficient. In the field, B. cucurbitae were more attracted to the local bait station than to the umbrella trap, while the two other fly species displayed equal attraction to both trap types. Our local bait station is a useful alternative to spot sprays of Synéis-appât and is now included in a local pest management program and is well accepted by farmers.

Patterns of species richness and diversity of insects associated with cucurbit fruits in the southern part of Cameroon

Patterns of species diversity and community structure of insects associated with fruits of domesticated cucurbits were investigated from January 2009 to 2011 in three localities from two agroecological zones in the southern part of Cameroon. Rarefaction curves combined with nonparametric estimators of species richness were used to extrapolate species richness beyond our own data. Sampling efforts of over 92% were reached in each of the three study localities. Data collected revealed a total of 66 insect morphospecies belonging to 37 families and five orders, identified from a set of 57,510 insects. The orders Diptera (especially Tephritidae and Lonchaeidae) and Hymenoptera (mainly Braconidae and Eulophidae) were the most important, in terms of both abundance and species richness on the one hand, and effects on agronomic performance on the other. Values for both the species diversity (Shannon and Simpson) and the species richness indices (Margalef and Berger-Parker) calculated showed that the insect communities were species-rich but dominated, all to a similar extent, by five main species (including four fruit fly species and one parasitoid). Species abundance distributions in these communities ranged from the Zipf-Mandelbrot to Mandelbrot models. The communities are structured as tritrophic networks, including cucurbit fruits, fruit-feeding species (fruit flies) and carnivorous species (parasitoids). Within the guild of the parasitoids, about 30% of species, despite their low abundance, may potentially be of use in biological control of important pests. Our field data contribute in important ways to basic knowledge of biodiversity patterns in agrosystems and constitute baseline data for the planned implementation of biological control in Integrated Pest Management.

Evaluation of cucurbitacin-based gustatory stimulant to facilitate cucumber beetle (Coleoptera: Chrysomelidae) management with foliar insecticides in melons

The bitter plant-derived compounds cucurbitacins are known to stimulate feeding of adult cucumber beetles (Coleoptera: Chrysomelidae). A cucurbitacin-based gustatory stimulant applied as a flowable bait combined with either spinosad or carbaryl was compared with foliar sprays of spinosad and carbaryl for controlling two cucumber beetle species (Diabrotica undecimpunctata undecimpunctata Mannerheim and Acalymma trivittatum Mannerheim) in honeydew melons (Cucumis melo L.). Field studies were conducted on the University of California-Davis plant pathology farm in 2008 and 2009. Beetle densities after applications and fruit damage from beetle feeding were compared among treatments. In addition, beetle survival was compared within field cages placed over the treated foliage infested with beetles. Using all three measures of efficacy, we determined that the addition of cucurbitacin bait had no effect on the level of cucumber beetle control with carbaryl in either 2008 or 2009. In both years, spinosad did not significantly reduce cucumber beetle densities in either field cages or field plots and did not reduce fruit damage relative to the untreated control. The addition of the bait to spinosad did not improve its efficacy. A laboratory bioassay of the spinosad formulation used in the field showed it had significant lethal effects on adults of both cucumber beetle species. Results indicated that the bait formulation used did not improve cucumber beetle control but may benefit from the addition of floral attractants or using a different type of cucurbitacin.

Effect of reproductive mode on host plant utilization of melon aphid (Hemiptera: Aphididae)

Variation in the reproductive mode of melon aphid Aphis gossypii Glover occurred on the large geographic scale, but the performance of different reproductive modes to use host plant is poorly understood. Life tables of melon aphid population that undergo the anholocyclic, androcyclic, and intermediate reproductive mode were conducted on different host plants. The results showed that the anholocyclic and androcyclic strains could become adults and produce offspring on cotton Gossypium hirsutum L., whereas the intermediate strain could not. The survival rate, net reproductive rate (R(0)), and intrinsic rate of natural increase (r(m)) of the androcyclic strain on cotton were significantly greater than that of the anholocyclic strain. The three strains could aptly use cucurbits host plants including cucumber Cucumis sativa L., pumpkin Cucurbita moschata (Duchesne ex Lam.), and zucchini Cucurbita pepo L.; survival rate and R(0) were not significantly different on these two host plants. Moreover, the r(m) of the anholocyclic strain on cucumber and the androcyclic strain on pumpkin and zucchini were significantly greater than that of the other two strains. The abilities of the three strains to use a host plant were flexible, because their r(m) on pumpkin or zucchini became equal after rearing for four successive generations; furthermore, the intermediate strain attained the ability to use cotton, and the performance of anholocyclic and intermediate strains to use cotton also significantly increased after feeding on pumpkin or zucchini for one or three generations. It was concluded that the reproductive mode and feeding experience affected the performance of melon aphid to use a host plant.

Mapping and validation of QTLs for resistance to aphids and whiteflies in melon

Aphis gossypii and Bemisia tabaci are severe hemipteran pests of melon crops and breeding for resistance to both insects is required to reduce pesticide use. Resistance was evaluated for its effect on behaviour and biotic potential of both hemipterans in a population of recombinant inbred lines (RILs) derived from the cross Védrantais x PI 161375. Insect variability was considered using two A. gossypii clones and two B. tabaci populations. Two additive QTLs affected the whiteflies. Four additive QTLs and two couples of epistatic QTLs affected the aphids. Amongst them, a major QTL affects both behaviour and biotic potential of A. gossypii and therefore a same R gene induces both antixenosis and antibiosis. This major QTL colocalizes with the Vat gene belonging to the NBS-LRR gene family. No loci affected both aphids and whiteflies contrary to what was observed for the Mi1.2 gene, a NBS-LRR gene in tomato. Original populations with different allelic compositions at QTLs affecting A. gossypii were built by one inter-crossing of RILs used for the mapping process. The genetic background was shown homogeneous between these populations what allowed validating QTLs and investigating the effect of allelic combinations at QTLs. Effects of QTLs were stronger than expected and some QTLs had a wider spectrum than expected. This strategy of validation appeared rapid and low cost.

Green lacewings (Neuroptera: Chrysopidae) associated with melon crop in Mossoró, Rio Grande do Norte State, Brazil

A survey of the green lacewings associated with the melon agroecosystem was carried out with the aim of including lacewings into the integrated management program of melon pests. Three species of this predator were found: Ceraeochrysa cubana (Hagen), Chrysoperla externa (Hagen) and Chrysoperla genanigra Freitas. A key to these species is presented.

A comparison of alternative plant mixes for conservation bio-control by native beneficial arthropods in vegetable cropping systems in Queensland Australia

Cucurbit crops host a range of serious sap-sucking insect pests, including silverleaf whitefly (SLW) and aphids, which potentially represent considerable risk to the Australian horticulture industry. These pests are extremely polyphagous with a wide host range. Chemical control is made difficult due to resistance and pollution, and other side-effects are associated with insecticide use. Consequently, there is much interest in maximising the role of biological control in the management of these sap-sucking insect pests. This study aimed to evaluate companion cropping alongside cucurbit crops in a tropical setting as a means to increase the populations of beneficial insects and spiders so as to control the major sap-sucking insect pests. The population of beneficial and harmful insects, with a focus on SLW and aphids, and other invertebrates were sampled weekly on four different crops which could be used for habitat manipulation: Goodbug Mix (GBM; a proprietary seed mixture including self-sowing annual and perennial herbaceous flower species); lablab (Lablab purpureus L. Sweet); lucerne (Medicago sativa L.); and niger (Guizotia abyssinica (L.f.) Cass.). Lablab hosted the highest numbers of beneficial insects (larvae and adults of lacewing (Mallada signata (Schneider)), ladybird beetles (Coccinella transversalis Fabricius) and spiders) while GBM hosted the highest numbers of European bees (Apis mellifera Linnaeus) and spiders. Lucerne and niger showed little promise in hosting beneficial insects, but lucerne hosted significantly more spiders (double the numbers) than niger. Lucerne hosted sig-nificantly more of the harmful insect species of aphids (Aphis gossypii (Glover)) and Myzus persicae (Sulzer)) and heliothis (Heliothis armigera Hübner). Niger hosted significantly more vegetable weevils (Listroderes difficillis (Germar)) than the other three species. Therefore, lablab and GBM appear to be viable options to grow within cucurbits or as field boundary crops to attract and increase beneficial insects and spiders for the control of sap-sucking insect pests. Use of these bio-control strategies affords the opportunity to minimise pesticide usage and the risks associated with pollution.

Host use of Bactrocera latifrons, a new invasive tephritid species in Tanzania

Bactrocera latifrons (Hendel) is a pest of Asian origin, first detected in Africa in 2006. We assessed the host utilization of this quarantine pest in Morogoro region, eastern central Tanzania, by collecting a wide range of cultivated and wild host plants of species belonging to Solanaceae and Cucurbitaceae from April 2007 to April 2008. Fruit were collected from 29 plant species and varieties (16 Solanaceae and 13 Cucurbitaceae) in all agroecological zones of Morogoro region. Twelve solanaceous fruit species yielded B. latifrons of which four are new host records: Capsicum annuum L. cov. longum A. DC., Capsicum chinense Jacq., Solanum sodomeum L., and Solanum scabrum Mill. Similarly, three cucurbitaceous fruit species provided positive rearings and are new host records: Citrullus lanatus (Thunb.) Matsum & Nakai, Cucumis dipsaceus L., and Momordica cf trifoliata L. The infestation rate and incidence of the pest was mainly high in the solanaceous hosts of nightshades (Solanum nigrum L. and Solanum scabrum) and African eggplants (Solanum aethiopicum Lam. and Solanum anguivi). In a host preference study involving limited number of cultivated solanaceous crops, S. scabrum was recorded as the most preferred host. The pest has been found to outnumber Bactrocera invadens (Drew et al.), Bactrocera cucurbitae (Coquillett), and Ceratitis capitata (Wiedemann) in most of the common solanaceous hosts.

Response of Melittia oedipus (Lepidoptera: Sesiidae) to visual cues is increased by the presence of food source

Visual and olfactory cues were shown to mediate short-distance orientation to different colors in the presence and in the absence of food in Melittia oedipus Oberthür (Lepidoptera: Sesiidae), a biological control agent of Coccinia grandis (L.) Voigt (Violales: Cucurbitaceae). Yellow was the color most preferred by M. oedipus, and adults landed significantly more on yellow paper moistened with honey-water. The next preferred colors were gray and white with the identical food source. Colors such as red, blue, green, brown, and black were least preferred by M. oedipus and attracted the adults on par with each other. The M. oedipus landings on petri dishes which held yellow-, gray-, and white-colored papers were significantly higher than the colorless petri dishes with olfactory stimuli only. There was no significant difference in landings on different-colored papers moistened with honey-water or with water alone in the morning compared with those in the evening. The cumulative response of M. oedipus to different-colored papers moistened with honey-water was significantly higher than the colored papers moistened with water only. Correspondingly, the response of M. oedipus to yellow-colored paper moistened with honey-water was significantly higher than the yellow-colored paper moistened with water only. Therefore, yellow paper moistened with honey-water can increase the feeding rate of M. oedipus and can be a potential technique in developing mass cultures for field release to control the invasive weed.

[Development and reproduction of B-biotype Bemisia tabaci on four cucurbitaceous host plants]

The study on the development and reproduction of B-biotype Bemisia tabaci on four cucurbitaceous host plants, i. e., cucumber, hairy gourd, bitter cucumber, and sponge gourd, showed that the one generation development duration of B. tabaci was the shortest (19.3 d) on hairy gourd and the longest (29.0 d) on bitter cucumber, the survival rate from egg to adult was the highest (92.85%) on cucumber and the lowest (53.08%) on bitter cucumber, the laid eggs were the most (187.4 eggs per female) on cucumber and the least (30.0 eggs per female) on bitter cucumber, and the longevity was the longest (25.2 d) on cucumber and the shortest (10.9 d) on bitter cucumber. The intrinsic rate of increase (r(m)) on cucumber, hairy gourd, bitter cucumber, and sponge gourd was 0.1453, 0.1429, 0.0616, and 0.1055, respectively. Among the test cucurbitaceous host plants, cucumber was the most suitable host plant for B. tabaci.

Development of immature stages and comparative demography of two cucurbit-attacking fruit flies in Reunion Island: Bactrocera cucurbitae and Dacus ciliatus (Diptera Tephritidae)

On Reunion Island, two species of Dacini, Bactrocera cucurbitae (Coquillett) and Dacus ciliatus Loew, infest 16 host plant species belonging to the family Cucurbitaceae from sea level to 1,600 m. These two species represent two primary pests of this plant family on the island. Melon fly, Bactrocera cucurbitae, and Ethiopian fruit fly, D. ciliatus, larval development was studied at four different constant temperatures (15, 20, 25, and 30 degrees C) with three host plants (cucumber, pumpkin, and squash). Adult life histories of these two species were studied at 25 degrees C with the three host plants. The results led to the conclusion that B. cucurbitae had a faster egg incubation time. Its preimaginal instars developed significantly faster than those of D. ciliatus independent of temperature. B. cucurbitae and D. ciliatus had similar mean preoviposition duration and egg hatching success. Fecundity was significantly higher for the melon fly on cucumber and pumpkin and lower on squash. Two distinctly different life- history patterns were evident: (1) later onset of reproduction, longer oviposition time, longer life span, and higher fecundity (B. cucurbitae) and (2) early reproduction, lower oviposition time, shorter life span, and lower fecundity (D. ciliatus). These results are useful for improving laboratory-rearing methods and for building simulation models to predict Dacini population dynamics.

Monitoring Diabrotica v. virgifera (Col.: Chrysomelidae) in southeastern Slovenia: increasing population trend and host spectrum expansion

Ever since the western corn rootworm (WCR) (Diabrotica virgifera virgifera), an alien invasive species from North America, has been introduced into Europe on at least 3 separate occasions, it spread within 15 years over the entire area of south-eastern and central Europe (except Denmark). Until quite recently, Zea mays L. was the only known host plant whereas in North America WCR also attacks members of the plant family Cucurbitaceae. In August of 2006, we were able to validate these findings also in the Old World by observing WCR visiting blossoms of oil pumpkin (Cucurbita pepo L.). Beside this first report of WCR on this regionally and economically important crop, a population increase in Gaberje near Lendava, Eastern Slovenia, was observed. Some future consequences of multiple hosts for integrated pest management (IPM) of WCR are being discussed.

Morphological discrimination of Aphis gossypii (Hemiptera: Aphididae) populations feeding on Compositae

Aphis gossypii Glover is a polyphagous aphid pest with a worldwide distribution. However, there is evidence that on a global scale the name A. gossypii is being applied to a number of forms with different life cycles and/or host-plant associations. Morphometric variation of A. gossypii samples from crops and non-cultivated plants in many parts of the world was examined, to determine whether this variation is correlated with the hosts from which the aphids originated. Samples of A. gossypii were collected from Cucurbitaceae and Malvaceae in Europe, and from Compositae in various parts of the world. Morphometric data for 13 parameters measured from 97 clonal lineages (728 specimens) and 27 field-collected samples (313 specimens) were analysed by a series of canonical variates analyses, using the field sample/clonal lineage as grouping factor. Clonal lineages were reared on a common host in controlled conditions to standardize the effect of host and environment on morphology. The analyses provided a clear morphometric separation of the aphids originating from Compositae and those collected on Cucurbitaceae and Malvaceae, regardless of the geographical origin of the aphids and the host plant on which they were reared. This indicates that within A. gossypii there are two widely distributed host races or subspecies with different plant family associations. The taxonomic implications are discussed.

Releases of Psyttalia fletcheri (Hymenoptera: Braconidae) and sterile flies to suppress melon fly (Diptera: Tephritidae) in Hawaii

Ivy gourd, Coccinia grandis (L.) Voigt, patches throughout Kailua-Kona, Hawaii Island, HI, were identified as persistent sources of melon fly, Bactrocera cucurbitae (Coquillett). These patches had a low incidence of Psyttalia fletcheri (Silvestri), its major braconid parasitoid natural enemy in Hawaii, and were used to evaluate augmentative releases of P. fletcheri against melon fly. In field cage studies of releases, numbers of melon flies emerging from ivy gourd fruit placed inside treatment cages were reduced up to 21-fold, and numbers of parasitoids were increased 11-fold. In open field releases of P. fletcheri into ivy gourd patches, parasitization rates were increased 4.7 times in release plots compared with those in control plots. However, there was no significant reduction in emergence of melon flies from fruit. In subsequent cage tests with sterile melon flies and P. fletcheri, combinations of sterile flies and P. fletcheri produced the greatest reduction (9-fold) in melon fly emergence from zucchini, Cucurbita pepo L. Reductions obtained with sterile flies alone or in combination with parasitoids were significantly greater than those in the control, whereas those for parasitoids alone were not. Although these results suggest that the effects of sterile flies were greater than those for parasitoids, from a multitactic melon fly management strategy, sterile flies would complement the effects of P. fletcheri. Cost and sustainability of these nonchemical approaches will be examined further in an ongoing areawide pest management program for melon fly in Hawaii.

Interactions between root-knot nematode Meloidogyne javanica and Fusarium wilt disease, Fusarium oxysporum f.sp. Melonis in different varieties of melon

Fusarium oxysporum f.sp. melonis and root-knot nematode (Meloidogyne javanica) are destructive pathogens on cucurbits in Varamin area of Iran. The interaction between two pathogens was studied on local melon cultivars, Garmsar and Sooski. Inoculum of Meloidogyne javanica was prepared on susceptible cultivar, Rutgers using single egg mass method in greenhouse. Inoculum of Fusarium oxysporum f.sp. melonis (race 1) was prepared using Richard solution. A concentration of 2 x 10(5) micro conidia of fungus and 2000, 3000, 4000, 5000 eggs of nematode was used in 1 kg of autoclaved soil. Plants were inoculated with nematode at 2-3 leave stage then with fungus 2 weeks after nematode inoculation. The experiment was conducted in factoriel design based on CRD with 20 treatments, including varieties in 2 levels (Garmsar and Sooski), nematode in 5 levels (0, 2000, 3000, 4000, 5000 eggs) and fungus in 2 levels (presence and absence) and 3 replicates. The index that evaluated were growth index including fresh and dry weight of shoot and root, height, Fusarium wilt index and root gall index. Results of this experiment showed that all of treatments comparison to control were significantly different (p = 0.05) in growth index. Combination of fungus and nematode (5000 eggs) caused the most decrease in growth index on Garmsar and Sooski.

Convergent evolution of cucurbitacin feeding in spatially isolated rootworm taxa (Coleoptera: Chrysomelidae; Galerucinae, Luperini)

Historically, chemical ecologists assumed that cucurbitacin feeding and sequestration in rootworm leaf beetles is a remnant of an ancient association between the Luperini (Coleoptera: Chrysomelidae; Galerucinae) and Cucurbitaceae (ancestral host hypothesis). Under this premise, rootworms that do not develop on cucurbits but undergo pharmacophagous forays for cucurbitacins are thought to do so to supplement novel host diets that lack these bitter compounds. The ancestral host hypothesis is supported from studies of pyrrolizidine alkaloid pharmacophagy in Lepidoptera but has not been subjected to phylogenetic analysis within the Luperini. New evidence that this feeding behavior is better correlated with an adult affinity for pollen than with larval host offers the possibility that Old and New World rootworm species with an affinity for cucurbitacins converged on this behavior through apomorphic taste receptor modifications (loose receptor hypothesis). Here we test the monophyly of cucurbitacin feeding within the Luperini by using nuclear and mitochondrial sequence data to infer phylogenetic relationships among 49 taxa representing tribes of the Galerucinae and subtribes of the Luperini. The resulting phylogenetic hypothesis is mostly concordant with existing tribal and subtribal delineations within the Subfamily Galerucinae sensu stricto (Galerucinae not including the flea beetles). The establishment of ancestry among the subtribes of the Luperini refutes the monophyly of cucurbitacin feeding and cucurbit specialization, with the New World Diabroticina being paraphyletic to the Old World Aulacophorina and cosmopolitan Luperina. These data unambiguously support the convergent evolution of cucurbitacin feeding in rootworms and are inconsistent with the ancestral host hypothesis.

Morphological, biochemical and molecular characterization of Herpetomonas samuelpessoai camargoi n. subsp., a trypanosomatid isolated from the flower of the squash Cucurbita moschata

We report the morphological, biochemical and molecular characteristics of a trypanosomatid isolated from the flower of Cucurbita moschata. Although the trypanosomatid was isolated from a plant, the lack of recognition of Phytomonas-specific molecular markers based on spliced-leader and ribosomal genes as well as by monoclonal antibodies specific for Phytomonas argues against assigning it to this genus. Because the isolate displayed typical opisthomastigote forms in culture, it is assigned to the genus Herpetomonas. Analysis of randomly amplified polymorphic DNA (RAPD) patterns and characterization of ribosomal SSU and ITS markers suggest that it is more closely related to H. samuelpessoai than to any other species. However, the presence of spined flagellates in culture (displaying lateral expansions of the plasma membrane originating near the flagellar pocket) and isolate-specific RAPD fingerprints argue strongly that the trypanosomatid belongs to a new subspecies, for which the name Herpetomonas samuelpessoai camargoi n. subsp. is proposed.

Local and systemic changes in squash gene expression in response to silverleaf whitefly feeding

Squash genes (SLW1 and SLW3) induced systemically after silverleaf whitefly feeding were identified. Differences in the local and systemic expression of SLW1 and SLW3 after feeding by the closely related silverleaf and sweetpotato whiteflies were observed. Temporal and spatial studies showed that SLW1 and SLW3 were induced when second, third, and fourth nymphal instars were feeding. Although only barely detected after wounding and bacterial infection, SLW1 and SLW3 RNAs were abundant during water-deficit stress. Treatments with wound/defense signal molecules showed that SLW1 RNAs accumulated in response to methyl jasmonate and ethylene, whereas SLW3 was not regulated by known wound/defense signals, suggesting utilization of a novel mechanism for defense signal transduction. SLW1 RNAs accumulated during floral and fruit development, whereas SLW3 RNAs were not detected during vegetative or reproductive development. The potential roles of SLW1, an M20b peptidase-like protein, and SLW3, a beta-glucosidase-like protein, in defense and the leaf-silvering disorder are discussed.

Local and systemic changes in squash gene expression in response to silverleaf whitefly feeding

Squash genes (SLW1 and SLW3) induced systemically after silverleaf whitefly feeding were identified. Differences in the local and systemic expression of SLW1 and SLW3 after feeding by the closely related silverleaf and sweetpotato whiteflies were observed. Temporal and spatial studies showed that SLW1 and SLW3 were induced when second, third, and fourth nymphal instars were feeding. Although only barely detected after wounding and bacterial infection, SLW1 and SLW3 RNAs were abundant during water-deficit stress. Treatments with wound/defense signal molecules showed that SLW1 RNAs accumulated in response to methyl jasmonate and ethylene, whereas SLW3 was not regulated by known wound/defense signals, suggesting utilization of a novel mechanism for defense signal transduction. SLW1 RNAs accumulated during floral and fruit development, whereas SLW3 RNAs were not detected during vegetative or reproductive development. The potential roles of SLW1, an M20b peptidase-like protein, and SLW3, a beta-glucosidase-like protein, in defense and the leaf-silvering disorder are discussed.