Cucurbit Fruit Research Articles

The oomycete broad‐host‐range pathogen Phytophthora capsici

Phytophthora capsici is a highly dynamic and destructive pathogen of vegetables. It attacks all cucurbits, pepper, tomato and eggplant, and, more recently, snap and lima beans. The disease incidence and severity have increased significantly in recent decades and the molecular resources to study this pathogen are growing and now include a reference genome. At the population level, the epidemiology varies according to the geographical location, with populations in South America dominated by clonal reproduction, and populations in the USA and South Africa composed of many unique genotypes in which sexual reproduction is common. Just as the impact of crop loss as a result of P. capsici has increased in recent decades, there has been a similar increase in the development of new tools and resources to study this devastating pathogen. Phytophthora capsici presents an attractive model for understanding broad-host-range oomycetes, the impact of sexual recombination in field populations and the basic mechanisms of Phytophthora virulence. Kingdom Chromista; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Phytophthora; Species capsici. Symptoms vary considerably according to the host, plant part infected and environmental conditions. For example, in dry areas (e.g. southwestern USA and southern France), infection on tomato and bell or chilli pepper is generally on the roots and crown, and the infected plants have a distinctive black/brown lesion visible at the soil line (Fig. 1). In areas in which rainfall is more common (e.g. eastern USA), all parts of the plant are infected, including the roots, crown, foliage and fruit (Fig. 1). Root infections cause damping off in seedlings, whereas, in older plants, it is common to see stunted growth, wilting and, eventually, death. For tomatoes, it is common to see significant adventitious root growth just above an infected tap root, and the stunted plants, although severely compromised, may not die. For many cucurbit fruit, the expanding lesions produce fresh sporangia over days (or even weeks depending on the size of the fruit) and the fruit often look as if they have been dipped in white powdered confectioner's sugar (Fig. 1). Generally, hyphae do not emerge from infected plants or fruit (common with Pythium infections) and all that is visible on the surface of an infected plant is sporangia. Phytophthora capsici presents an oomycete worst-case scenario to growers as it has a broad host range, often produces long-lived dormant sexual spores, has extensive genotypic diversity and has an explosive asexual disease cycle. It is becoming increasingly apparent that novel control strategies are needed to safeguard food production from P. capsici and other oomycetes. Considering that P. capsici is easy to grow, mate and manipulate in the laboratory and infects many plant species, this pathogen is a robust model for investigations, particularly those related to sexual reproduction, host range and virulence. Phytophthora capsici genome database: http://genome.jgi-psf.org/Phyca11/Phyca11.home.html. Molecular tools to identify Phytophthora isolates: http://phytophthora-id.org.

Differences in virulence of Phytophthora capsici isolates from a worldwide collection on host fruits

Phytophthora capsici causes root, crown, and fruit rot of vegetable and tropical hosts. Cucumber, zucchini, tomato, and pepper fruits were inoculated using 6-mm-diameter agar plugs of P. capsici, incubated in clear plastic boxes at room temperature (25 ± 2°C and 100% relative humidity), and virulence was estimated by measuring the lesion diameter, pathogen growth diameter, and pathogen sporulation density three (cucumber, zucchini) or four (tomato, pepper) days later. When isolates were grouped by genetic cluster, significant differences in virulence were observed on cucumber and zucchini, with isolates belonging to genetic cluster five causing larger lesions than isolates from genetic cluster six. On tomato, no significant differences were observed for isolates grouped by genetic cluster, but isolates from vegetable crops were generally more virulent than isolates from tropical hosts. Isolates from fabaceous hosts sporulated better on cucumber fruits than isolates from solanaceous hosts. Isolates from vegetable hosts sporulated better on zucchini than isolates from tropical hosts. No significant differences in lesion diameter were noted on pepper when isolates were grouped by host family of origin or genetic cluster, but differences in pathogen sporulation were apparent by host family. Our findings suggest that isolate characteristics such as host family of origin and genetic cluster membership may be used to guide initial isolate selection for cucurbit fruit resistance screening. Final isolate selection should incorporate the phenotypic and genetic diversity of P. capsici, including isolates with differing virulence to the host organ of interest.

Semitic-language records of snake melons (Cucumis melo, Cucurbitaceae) in the medieval period and the “piqqus” of the “faqqous”

The snake melon, Cucumis melo subsp. melo Flexuosus Group, is a cucurbit crop that was grown and esteemed in Mediterranean lands in antiquity and classical times. Images of snake melons appear in ancient Egyptian wall paintings and sculptures and in mosaics from the Roman Empire. The sikyos of Greek, the cucumis of Latin, and the qishu’im of Hebrew, thought by many to be cucumbers, Cucumis sativus, have now been identified as snake melons. Less iconographic and written evidence exists concerning the appreciation of snake melons during the medieval period. The present work focuses on some philologically based evidence of the importance of snake melons leading into and including the medieval period, with two specific objectives. One was to trace the records of the Hebrew epithet piqqus, which applied to removal of the hairs of young cucurbit fruits, and the Arabic epithet faqqous, used historically and to the present day to designate snake melons. Another objective was to re-affirm how piqqus was actually conducted, as mandated in the second-century code of Jewish Oral Law known as the Mishna. Various conjugational forms of the Hebrew word piqqus were found in writings dating from 200 CE to approximately 600 CE. Evidence is presented that further establishes the exact meaning of piqqus as the rubbing off of the hairs of young cucurbit fruits. The Arabic word faqqous was found in writings dating from the beginning of the tenth century and through to the end of the medieval period in the fifteenth century, the writers hailing from Andalusia in the west to Iraq in the east. These writings suggest that the snake melon was a familiar vegetable across a wide geographic belt throughout the medieval period.

Transgenic watermelon lines expressing the nucleocapsid gene of Watermelon silver mottle virus and the role of thiamine in reducing hyperhydricity in regenerated shoots

Viral diseases are very detrimental to watermelon production. Watermelon silver mottle virus (WSMoV) is a major limiting factor for the production of watermelon and other cucurbit fruits. There are no effective natural sources of resistance to WSMoV, making transgenic resistance an appropriate solution for attenuating virus infection. Hyperhydricity is an important problem in watermelon culture in vitro, resulting from lower multiplication rates, poor quality shoots and tissue necrosis. In this study, we report an Agrobacterium-mediated genetic transfer protocol for commercial watermelon cultivars expressing the nucleocapsid (N) gene of WSMoV and a suitable approach to overcome hyperhydricity in watermelon culture in vitro. Murashige and Skoog (MS) salts containing Schenk and Hildebrandt (SH) vitamins + 50 mg l−1 thiamine HCl could diminish the hyperhydric phenotype. The proximal halves of cotyledons from 3-day-old seedlings were cut into 1.5 × 1.5 mm segments as explants. Four days after co-cultivation, the explants were transferred to a selection medium for shoot regeneration. The putative transgenic shoots developed within 6 weeks of culture and were then transferred to stringent medium for 8 weeks to eliminate ‘escape type’ shoots. Fifty putative transgenic watermelon lines were obtained from three cultivars. PCR and Southern blot analysis confirmed that the foreign gene was incorporated into the genomic DNA of the transgenic lines.

Sucrose accumulation in watermelon fruits: Genetic variation and biochemical analysis

Sugar accumulation, the key process determining fruit quality, is controlled by both the translocation of sugars and their metabolism in developing fruits. Sugar composition in watermelon, as in all cucurbit fruits, includes sucrose, fructose and glucose. The proportions of these three sugars are determined primarily by three enzyme families: invertases, sucrose synthases (SuSys) and sucrose phosphate synthases (SPSs). The goal of the present research was to explore the process of sugar metabolism in watermelon fruits. Crosses between the domestic watermelon ( Citrullus lanatus) and three wild species provided a wide germplasm to explore genetic variability in sugar composition and metabolism. This survey demonstrated great genetic variability in sugar content and in the proportions of sucrose, glucose and fructose in mature fruits. Genotypes accumulating high and low percentage of sucrose provided an experimental system to study sugar metabolism in developing fruits. Insoluble invertase activity was high and constant throughout fruit development in control lines and in genotypes accumulating low levels of sucrose, while in genotypes accumulating high levels of sucrose, activity declined sharply 4 weeks after pollination. Soluble acid invertase activity was significantly lower in genotypes accumulating high levels of sucrose than in low-sucrose-accumulating genotypes. Conversely, activities of SuSy and SPS were higher in the high-sucrose-accumulating genotypes. The present results establish that, within the genus Citrullus, there are genotypes that accumulate a high percentage of sucrose in the fruit, while others accumulate high percentages of glucose and fructose. The significant negative correlation between insoluble invertase activity and fruit sucrose level suggests that sucrose accumulation is affected by both phloem unloading and sugar metabolism.

Age-related Resistance of Diverse Cucurbit Fruit to Infection by Phytophthora capsici

Phytophthora capsici causes severe losses in vegetable production, including many cucurbit crops. Our previous work showed that cucumber (Cucumis sativus) fruit are most susceptible to P. capsici when they are very young and rapidly elongating, but develop resistance as they approach full length at 10 to 12 days postpollination (DPP). In this study, fruit from seven additional cucurbit crops representing four species, melon (Cucumis melo), butternut squash (Cucurbita moschata), watermelon (Citrullus lanatus), and zucchini, yellow summer squash, acorn squash, and pumpkin (Cucurbita pepo), were tested for the effect of fruit development on susceptibility to P. capsici. Field-grown fruit of the different crops varied in overall susceptibility. Zucchini and yellow summer squash were the most susceptible, with the majority of fruit exhibiting water-soaking symptoms within 24 hours postinoculation. Fruit from all of the crops exhibited size-related decrease in susceptibility, but to varying degrees. Cucumber had the most pronounced effect. In infested fields, cucumber fruit were found to be most frequently infected at the blossom end. Comparison of the peduncle and blossom end showed a difference in susceptibility along the length of the fruit for cucumber, butternut squash, and zucchini. Greenhouse-grown, hand-pollinated pumpkin, acorn squash, and butternut squash showed an age-related decrease in susceptibility similar to field-grown fruit. For all of these fruit, a pronounced reduction in susceptibility accompanied the transition from the waxy green to green stage at ≈3 to 8 DPP.

Sewage and community shower drains are environmental reservoirs of Fusarium solani species complex group 1, a human and plant pathogen

In two recent studies, clinical isolates in the Fusarium solani species complex (FSSC) were sequenced; one of the most common lineages was FSSC Group 1 (FSSC 1), a phylogenetic species that is synonymous with F. solani f. sp. cucurbitae race 2, a pathogen of cucurbit fruits. FSSC 1 was also identified in sink and shower drains in two hospitals. The environmental sources of FSSC 1 are important for understanding the epidemiology of both human and plant diseases caused by this organism. FSSC 1 was detected in sewage influent at all six tested urban wastewater treatment plants (WWTPs) in California with a concentration ranging from 75 to 413 colony-forming units (cfu) l(-1), a mean of 246 +/- 52 cfu l(-1) and a median of 254 cfu l(-1). During the treatment process, the concentration of FSSC 1 in the solid and liquid fractions diminished. FSSC 1 was detected in five and six of 14 community shower drains by culturing and polymerase chain reaction, respectively, whereas FSSC DNA was detected in all drains. FSSC accounted for 17 +/- 6% (n = 14) of the total fungal DNA in the drains. FSSC 1 was rarely isolated from post-harvest cucurbit fruits and was not found in cucurbit fields in California.

Fusarium solani species complex isolates conspecific with Fusarium solani f. sp. cucurbitae race 2 from naturally infected human and plant tissue and environmental sources are equally virulent on plants, grow at 37°C and are interfertile

SummaryIn a previous taxonomic study based on multilocus sequencing of Fusarium from clinical specimens and hospital environments, the most common lineage was Fusarium solani species complex group 1 (FSSC 1) which is conspecific with F. solani f. sp. cucurbitae race 2, a pathogen of cucurbit fruits. The aims of our study were to determine if clinical and environmental isolates of FSSC 1 are plant pathogens and members of the same biological species as cucurbit isolates, and to determine if all isolates can germinate, grow and sporulate at 37°C. Isolates from the different sources did not differ in virulence on zucchini fruits. All FSSC 1 isolates were pathogenic and produced more rot than FSSC isolates from plant hosts other than cucurbits. Both mating types were found among isolates from each of the sources, and all isolates were sexually compatible with cucurbit isolates. All isolates germinated, grew and sporulated at 37°C. This is the first report in which plant pathogenicity has been verified for a collection of human clinical isolates. Our data are consistent with the hypothesis that all FSSC 1 isolates, regardless of source, are a single biological species, equally virulent plant pathogens and tolerant of the human body temperature.

Heterosis in Bittergourd

Summary Bittergourd is an important cucurbit fruit vegetable grown in the tropics. It has rich nutritional and medicinal value. Hybrids are becoming popular in this crop. Gynoecy is also reported in this crop which could be a useful tool to exploit heterosis on commercial scale with more cheaper rates. But at present hybrid seed is produced by hand pollination without emasculation.

Cucurbits under protected cultivation

Cucurbits under protected cultivation

Purification of an Alpha — Amylase Inhibitor from Seeds of Little Millet (Panicum sumatrens Roth)

An insect specific alpha-amylase inhibitor (α-Al) from seeds of CO3 variety of little millet (Panicum sumatrens Roth) was isolated and purified to homogeneity following ammonium sulfate precipitation, successive chromatographic separations on Sephadex G75 and CM- cellulose columns and finally through RP-HPLC. Western blotting using polyclonal antibodies raised against the purified α-Al identified a unique band. The purified protein was found to be a non-glycosylated polypeptide with a molecular weight of 36kD. The isolated inhibitor severely inhibited the larval midgut alpha-amylases of tomato fruit borer (Helicoverpa armigera), brinjal shoot and fruit borer (Leucinodes orbonalis) and cucurbit fruit fly (Dacus cucurbitae).

Mefenoxam Insensitivity and the Sexual Stage of Phytophthora capsici in Michigan Cucurbit Fields

ABSTRACT The potential for outcrossing, occurrence of oospores, and inheritance of mefenoxam sensitivity was assessed in naturally occurring populations of Phytophthora capsici. Between 1997 and 1998, 14 farms were sampled, with 473 isolates recovered from cucurbit hosts and 30 from bell pepper. The A1 and A2 compatibility types were recovered in a roughly 1:1 ratio in 8 of 14 farms with sample sizes larger than 15. In 1997, one isolate was designated as insensitive and four as sensitive to mefenoxam. In 1998, 55% of the 498 isolates sampled were sensitive, 32% were intermediate, and 13% were fully insensitive to mefenoxam. In vitro characterization of mefenoxam sensitivity was conducted by crossing field isolates. Chi-square analysis of crosses between sensitive, intermediately sensitive, and insensitive isolates indicate that mefenoxam insensitivity segregated as an incompletely dominant trait unlinked to compatibility type (P = 0.05). Oospores were observed in diseased cucurbit fruit from four farms in 1998, and 223 oospore progeny were recovered from a single diseased cucumber. All six mefenoxam sensitivity-compatibility type combinations were present in these oospore progeny and within single fields. Based on these findings, we conclude that oospores likely play a role in the survival of P. capsici and that sexual recombination may significantly influence population structure.

A novel alkaline alpha-galactosidase from melon fruit with a substrate preference for raffinose

The cucurbits translocate the galactosyl-sucrose oligosaccharides raffinose and stachyose, therefore, alpha-galactosidase (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) is expected to function as the initial enzyme of photoassimilate catabolism. However, the previously described alkaline alpha-galactosidase is specific for the tetrasaccharide stachyose, leaving raffinose catabolism in these tissues as an enigma. In this paper we report the partial purification and characterization of three alpha-galactosidases, including a novel alkaline alpha-galactosidase (form I) from melon (Cucumis melo) fruit tissue. The form I enzyme showed preferred activity with raffinose and significant activity with stachyose. Other unique characteristics of this enzyme, such as weak product inhibition by galactose (in contrast to the other alpha-galactosidases, which show stronger product inhibition), also impart physiological significance. Using raffinose and stachyose as substrates in the assays, the activities of the three alpha-galactosidases (alkaline form I, alkaline form II, and the acid form) were measured at different stages of fruit development. The form I enzyme activity increased during the early stages of ovary development and fruit set, in contrast to the other alpha-galactosidase enzymes, both of which declined in activity during this period. In the mature, sucrose-accumulating mesocarp, the alkaline form I enzyme was the major alpha-galactosidase present. We also observed hydrolysis of raffinose at alkaline conditions in enzyme extracts from other cucurbit sink tissues, as well as from young Coleus blumei leaves. Our results suggest different physiological roles for the alpha-galactosidase forms in the developing cucurbit fruit, and show that the newly discovered enzyme plays a physiologically significant role in photoassimilate partitioning in cucurbit sink tissue.

Cucurbit Seed Development and Production

Seed production in the family Cucurbitaceae is more complicated than in dry-seeded grain crops because seeds mature within a moist fruit and are often held at high moisture content for several weeks before seed harvest. Muskmelon (Cucumis melo L.), a member of this family, was used as a model system to contrast seed development with crops that are dry at maturity. A detailed time course for `Top Mark' fruit and seed development is presented based on previous studies. In muskmelon fruit, precocious germination is inhibited osmotically by the low water potential of the surrounding fruit tissue. Muskmelon seeds exhibit primary dormancy that affects viability very early in development but has a greater effect on seed vigor and is removed by afterripening during dry storage. Osmotically distended or fish-mouth seeds are dead seeds that occur in cucurbit seed lots after aging kills the embryo without disrupting the semipermeable endosperm that completely surrounds and protects the embryo. Cucurbit seed crops should be harvested before the onset of fruit senescence to prevent aging of the seeds inside. Open-pollinated cucurbit seed crops are frequently once-over mechanically harvested. Mechanical harvesting combines seeds from many stages of development into a single seed lot, which may adversely affect quality and increase seed to seed variability. Hand harvesting cucurbit fruit at the optimal stage of development could improve seed quality in some instances but is more costly and time consuming and would increase production costs.

Current Status of Cucurbit Anthracnose

Anthracnose is a destructive foliage and fruit disease of cucurbits worldwide, particularly on cucumber, watermelon, and cantaloupe. Three fungal taxa have been implicated in the cucurbit anthracnose complex [Colletotrichum orbiculare (CO), C. magna (CM), and the putative teleomorph Glomerella cingulata var. orbiculare (GC)]. In the past 7 years we have assembled a large geographically diverse collection of cucurbit isolates that have been characterized for virulence, vegetative (heterokaryon) compatibility, and mitochondrial and nuclear DNA RFLPs. All isolates that are pathogenic on cucurbit foliage are CO, belong to one of the four VCGs, and belong to a single mtDNA RFLP haplotype. Three races of CO (1, 2, and 2B) can be distinguished by their disease reactions on cucumber (`Marketer' and `H19') and watermelon (`Black Diamond' and `Charleston Gray') differentials. Race 1 (cucumber pathogen) and race 2 (watermelon pathogen) were the most common. Examination of virulence on cucurbit fruit indicates that CM and GC are more aggressive than CO, indicating that they could primarily be fruit-rot pathogens. Race 1 and 2 have been used effectively for screening disease resistance in cucumber and watermelon. Isolates of CM, GC, and Colletotrichum spp. recovered from fruit lesions were not pathogenic or were weakly virulent on cucurbit foliage and were diverse with regard to VCGs, nuDNA, and mtDNA RFLPs. However, CM and GC were more virulent on cucurbit fruit than CO.

Changes in soluble sugar and activity of α-galactosidases and acid invertase during muskmelon ( Cucumis melo L.) fruit development

Summary Soluble sugar, a-galactosidase (EC 3.2.1.22) and soluble acid invertase (EC 3.2.1.26) were determined in fruit tissues and peduncles of melon (Cucumis melo L. cv. Ranjadew) in the course of fruit development. Fruit development was followed from anthesis to fruit abscission (53-55 days after anthesis). At fruit maturity, the exo-mesocarp had the highest sugar content followed by endocarp and placenta, seeds and peduncles. Stachyose and raffinose were present in all fruit tissues and peduncles at all stages of development. Stachyose was the main sugar of the peduncles. In all other fruit tissues, sucrose and the hexoses prevailed. The sugar composition of phloem exudate collected from peduncles cut near stem or fruit was identical, indicating that translocate is conducted along the phloem of fruit peduncles unchanged. Acid invertase activity followed optimum curves, alkaline α-galactosidase activity declined and acid α-galactosidase slightly increased during fruit development, a-galactosidase and invertase activities are closely correlated with the distribution of raffinose oligosaccharides, sucrose and hexoses. Our data confirm a recent conclusion that raffinose oligosaccharides are translocated within the phloem into Cucurbit fruits and seeds and that oligosaccharides are effectively decomposed here by a-galactosidases.

PATHOGENICITY AND VIRULENCE OF COLLETOTRICHUM SPECIES ON CUCURBIT FRUIT

Three taxa, Colletotrichum orbiculare, the unconfirmed teleomorph of C. orbiculare (Glomerella cingulata var. orbiculare), and C. magna, have been reported to cause anthracnose of cucurbits. In a previous study, virulence, vegetative compatibility, and mtDNA RFLPs have been used to examine these taxa. The three taxa can be distinguished based on mtDNA RFLPs. Under controlled greenhouse inoculation tests, only isolates of C. orbiculare (CO) from cucurbit hosts were highly virulent on cucurbit foliage; isolates of G. cingulata (GC) and C. magna (CM), and CO from cocklebur hosts were weakly virulent or avirulent. The majority of CM and GC isolates were recovered from fruit, whereas most CO isolates were recovered from foliage. A study was conducted to evaluate the pathogenicity and virulence of anthracnose isolates on cucurbit fruit. Twenty-seven isolates of the three taxa were selected based on the host and geographic origin, mtDNA RFLP haplotype, vegetative compatibility group, and race. Mature fruit from cucumber cultivars Marketer (susceptible) and H19 (resistant) and watermelon cultivars Black Diamond (susceptible) and Charleston Gray (resistant) were used. Fruit were inoculated by placing Torula yeast agar inoculum plugs (8mm in diameter) into wounds. Following inoculation, the wounds were covered with Parafilm and incubated for 8 days at 25C at 100% RH. On the third day the Parafilm was removed from the wound. Disease symptoms were evaluated by measuring lesion diameter and depth and evaluating the presence or absence of sporulation. All three anthracnose taxa are capable of infecting cucurbit fruit. CM and GC isolates were more virulent than CO isolates on cucumber. In contrast, on `Black Diamond', CO isolates were more virulent than CM and GC isolates. No significant differences in virulence were observed on `Charleston Gray'. There were no significant differences in virulence between the races of CO except on `Charleston Gray', where race 2 isolates were significantly more virulent than race 1. CO isolates from cocklebur were only weakly virulent on cucurbit fruit.

Pest management and pollination of cantaloupes grown under spunbonded row covers in West Africa

SummaryCantaloupe is non parthenocarpic and requires insects for pollination. However, it is severely affected by sap-sucking insects, the viruses they vector, and cucurbit fruit flies throughout West Africa. Our study was conducted in Senegal to evaluate spunbonded row cover as an integrated production tool with special reference to pest management and pollination. We used an andromonoecious cultivar and compared an open treatment with four cover treatments. In the first two treatments, the covers were removed at the onset of fruiting to allow open pollination. The fabric was laid directly on the plants in one treatment and arranged in small tunnels in the other. In the other two treatments, small tunnels of fabric were maintained over the plants for 20 d after the onset of fruiting. In one, an end of the tunnel was cut open to allow open pollination while in the last treatment, the tunnel was kept closed and pollination was provided by a colony of African honey bees in a multiple-entrance hive. All plants were sprayed with fungicides as needed, but only the plants in the open or those with the cover removed were treated with insecticides. Honey bees foraged in all plots and pollination was not a limiting factor in any of the treatments. Chemical applications alone provided poor protection and yielded an average of 0.18 kg of export-grade fruit per plant. Removal of the covers at the onset of fruiting resulted in severe insect damage and plant losses regardless of the layout of the cover and the final yield of export-grade fruit was 0.40 kg per plant. Tunnels with the opening at one end allowed adequate open pollination while maintaining a significant level of protection from insect pests and gave a yield of 0.56 kg of export-grade fruit per plant. The closed tunnels with beehives gave the best results from the standpoint of plant growth and development as well as a yield of export-grade fruit of 0.97 kg per plant.

Taxonomic notes on some dacine (Diptera: Tephritidae) fruit flies associated with citrus, olives and cucurbits

AbstractThe taxonomic identity and synonymy of four serious fruit fly pests, one of olives in Europe, and three Oriental species, two associated with citrus fruits and one with cucurbit fruits and vegetable, is clarified.PolistomimetesEnderlein is a new synonym ofTetradacusMiyake, which was originally described as a subgenus ofDacus, but is newly placed as a subgenus ofBactrocera. HeterodaculusHardy is removed from synonymy withPolistomimetes. Mellesis citriChen is a new synonym ofB. minax(Enderlein);D. cheniChao is a new synonym ofB. tsuneonis(Miyake); andD. nubilusHendel is replaced in synonymy withB. tau(Walker).Callantra splendidaPerkins andD. discipennisWalker are transferred to the genusBactroceraMacquart. The limits of the subgeneraB. (Daculus) andB. (Tetradacus) are discussed; it is concluded that oviscape form separates those subgenera.B. (Daculus) includes the olive fly,B. oleae(Gmelin) andB. (Tetradacus) includes the Oriental citrus flies,B. minax(Enderlein) andB. tsuneonis(Miyake), plus three other species. It is also concluded that the presence or absence of anterior supra-alar setae and prescutellar acrostichal seatae should not be used in the diagnosis ofBactrocerasubgenera. A lectotype ofPolistomimetes minaxEnderlein is designated.

Weather‐based models to predict the population densities of melon fruit fly,Dacus cucurbitaeCoq.

Abstract Based on the weekly male catches in pheromone traps and weather data for 2 years (1985, 1986), regression models were developed to predict the densities of melon fruit fly, Dacus cucurbitae Coq., which is an important pest of cucurbit and solanaceous fruits. Among the simple linear regression models, the model SQRT (male counts + 1) = —5.37+0.75 (mean daily temperature in degrees Celsius) was the best, as it explained the highest (68%) variability. The model log(male counts + 1) = —7.54 + 0.35 (maximum temperature) + 0.63 (minimum temperature) —0.02 (maximum × minimum temperature) explained 80% variability, and was considered to be the best for forecasting fruit fly populations.