Genetic variation among populations of the Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae) in Morocco and Syria

The RAPD-PCR technique was used to study genetic variation within and among geographical populations of the Hessian fly, Mayetiola destructor (Say), from Morocco and Syria, associated with the fly's ability to overcome resistance in three wheat cultivars containing H5, H13 and H22 resistance genes. Variation was detected both for the level of susceptibility of the cultivars and RAPD profiles of M. destructor populations. By the use of RAPD-PCR, high genetic variability was detected among individuals and populations of M. destructor within and between areas separated geographically. The DNA fingerprints of populations of M. destructor were area-specific with Nei's measures of genetic distance ranging from 0.156 (between Abda and Beni Mellal, Morocco) to 1.977 (between Marchouch, Morocco and Lattakia, Syria). Cluster analysis of the genetic distances among the populations, identified the Syrian population as an outlier. A highly significant correlation (r = 0.81) observed between the genetic and geographic distances among the populations, provided genetic support for dispersal of the fly from its presumed origin in West Asia to Morocco.     

Virulence of Hessian fly (Diptera: Cecidomyiidae) in the Fertile Crescent

The Hessian fly, Mayetiola destructor (Say), is an important insect pest of wheat (Triticum spp.) in North Africa, North America, southern Europe and northern Kazakhstan. Both wheat and this pest are believed to have originated from West Asia in the Fertile Crescent. The virulence of a Hessian fly population from Syria against a set of cultivars carrying different resistance genes, in addition to other effective sources with unknown genes, was determined in the field and laboratory at the International Center for Agricultural Research in the Dry Areas (ICARDA) during the 2005/2006 cropping season. Only two resistance genes (H25 and H26) were effective against the Syrian Hessian fly population, making it the most virulent worldwide. This high virulence supports the hypothesis that Hessian fly coevolved with wheat in the Fertile Crescent of West Asia. The ICARDA screening programme is using this Hessian fly population to identify new resistance genes to this pest.     

Uncoupling of growth and cytological development in egg follicles ofHeteropeza pygmaea (Dipt., Cecidomyiidae)

Summary Oogenesis of egg follicles in paedogenetic reproduction of the gall midgeHeteropeza pygmaea is accompanied by a relatively slight growth of the oocyte. Egg growth takes place mainly during embryonic development. The nurse chamber in the egg follicle degenerates only at the beginning of embryogenesis. When ovaries of the female larvae are cultured in vitro under male-determining conditions, the ovaries produce mostly male-determined egg follicles. These follicles show nurse chamber degeneration and they grow to about the size of an egg in late cleavage division or blastoderm stage developing in situ, but cytological development invariably stops at the first or second meiotic division. Thus, growth and cytological development in such follicles are uncoupled. The presence of a meiotic block in paedogenetically developing follicles ofH. pygmaea gives a clue to the mode of evolution of paedogenetic reproduction.Dedicated to Professor Dr. Hans Bauer on the occasion of his 75th birthday     

No fitness cost for wheat's H gene-mediated resistance to Hessian fly (Diptera: Cecidomyiidae)

Resistance (R) genes have a proven record for protecting plants against biotic stress. A problem is parasite adaptation via Avirulence (Avr) mutations, which allows the parasite to colonize the R gene plant. Scientists hope to make R genes more durable by stacking them in a single cultivar. However, stacking assumes that R gene-mediated resistance has no fitness cost for the plant. We tested this assumption for wheat's resistance to Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). Our study included ten plant fitness measures and four wheat genotypes, one susceptible, and three expressing either the H6, H9, or H13 resistance gene. Because R gene-mediated resistance has two components, we measured two types of costs: the cost of the constitutively-expressed H gene, which functions in plant surveillance, and the cost of the downstream induced responses, which were triggered by Hessian fly larvae rather than a chemical elicitor. For the constitutively expressed Hgene, some measures indicated costs, but a greater number of measures indicated benefits of simply expressing the H gene. For the induced resistance, instead of costs, resistant plants showed benefits of being attacked. Resistant plants were more likely to survive attack than susceptible plants, and surviving resistant plants produced higher yield and quality. We discuss why resistance to the Hessian fly has little or no cost and propose that tolerance is important, with compensatory growth occurring after H gene-mediated resistance kills the larva. We end with a caution: Given that plants were given good growing conditions, fitness costs may be found under conditions of greater biotic or abiotic stress.     

Approved quarantine treatment for Hessian fly (Diptera: Cecidomyiidae) in large-size hay bales and Hessian fly and cereal leaf beetle (Coleoptera: Chrysomelidae) control by bale compression

A quarantine treatment using bale compression (32 kg/cm2 pressure) and phosphine fumigation (61 g/28.3 m3 aluminum phosphide for 7 d at 20 degrees C) was approved to control Hessian fly, Mayetiola destructor (Say), in large-size, polypropylene fabric-wrapped bales exported from the western states to Japan. No Hessian fly puparia (45,366) survived to the adult stage in infested wheat, Triticum aestivum L., seedlings exposed to the treatment in a large-scale commercial test. Daily temperatures (mean +/- SEM) inside and among bales in three test freight containers were 17.8 +/- 0.2 front top, 17.0 +/- 0.2 front bottom, 17.3 +/- 0.2 middle bale, 15.7 +/- 0.3 middle air, 18.5 +/- 0.1 back top, and 18.1 +/- 0.1 degrees C back bottom, allowing the fumigation temperature to be established at > or = 20 degrees C. Mean fumigant concentrations ranged from 208 to 340 ppm during the first 3 d and ranged from 328 to 461 ppm after 7 d of fumigation. Copper plate corrosion values inside the doors, and in the middle of the large-size bales in all locations indicated moderate exposure to hydrogen phosphide (PH3). PH3 residues were below the U.S. Environmental Protection Agency tolerance of 0.1 ppm in animal feeds. The research was approved by Japan and U.S. regulatory agencies, and regulations were implemented on 20 May 2005. Compression in large-size bale compressors resulted in 3-3.6 and 0% survival of Hessian fly puparia and cereal leaf beetle, Oulema melanopus (L.), respectively. Bale compression can be used as a single treatment for cereal leaf beetle and as a component in a systems approach for quarantine control of Hessian fly.     

Lygid bug damage as a pod access mechanism for Dasineura brassicae (Dipt., Cecidomyiidae) oviposition

Abstract: In a no-choice laboratory experiment, damage to Brassica napus pods created by Lygus feeding showed equivalent levels of Dasineura brassicae oviposition as both Ceutorhynchus assimilis damage and artificial injury (P > 0.05). No oviposition was recorded on undamaged controls (P < 0.01). Although Lygus damage provided equal pod access in the laboratory, lygid species are unlikely to be as efficacious a field vector as C. assimilis , primarily due to their less synchronous phenology.     

Distribution,population dynamics and damage of Hessian fly,Mayetiola destructor (Diptera: Cecidomyiidae) in North Tunisia

A three years survey and monitoring studies (2013–2014–2015) were carried out through 4 regions of north Tunisia in order to follow the evolution of the distribution, the frequency of occurrence and damage caused by the Hessian fly Mayetiola destructor (Say) to bread wheat (Triticum aestivum L.) and durum wheat (Triticum durum Desf). Moreover, the effectiveness of resistance genes H3, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, H22, H23, H25 and H26 to protect wheat from Hessian fly attack was assessed in natural field and under controlled laboratory conditions at INRAT-Kef Station. Results showed that Hessian fly was detected in 60.33% and 51.5% of all sampled durum and bread wheat fields, respectively. This pest was more frequent with a higher percentage of infestation in semi-arid regions. Indeed, during 2013, infestation rate attained 12.39% in Kef region against 0.9% registered in Bizerte region. In order to update information about the annual number of generations, we surveyed the population dynamic of Hessian fly in Kef region. Three generations of the fly were counted annually on wheat, with two complete and one incomplete generation. This insect affects host plant growth at different developmental stages. Plant height was the most affected parameter followed by shoot dry weight and tiller number. Field investigations on host resistance revealed that among the 16 tested resistance genes, and only three were strictly effective (H22, H25 and H26). The resistance genes H5, H9, H13 and H9H13 have also conferred high levels of protection against Hessian fly. This work indicated that H22, H25 and H26 genes could be incorporated into Tunisian wheat varieties and released to farmers to manage the threat due to Hessian fly attacks.     

A reproductive fitness cost associated with Hessian fly (Diptera: Cecidomyiidae) virulence to wheat's H gene-mediated resistance

We studied whether adaptation of the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), to plant resistance incurs fitness costs. In this gene-for-gene interaction, adaptation to a single H resistance gene occurs via loss of a single effector encoded by an Avirulence gene. By losing the effector, the adapted larva now survives on the H gene plant, presumably because it evades the plant's H gene-mediated surveillance system. The problem is the Hessian fly larva needs its effectors for colonization. Thus, for adapted individuals, there may be a cost for losing the effector, with this then creating a trade-off between surviving on H-resistant plants and growing on plants that lack H genes. In two different tests, we used wheat lacking H genes to compare the survival and growth of a nonadapted strain to two H-adapted strains. The two adapted strains differed in that one had been selected for adaptation to H9, whereas the other strain had been selected for adaptation to H13. Tests showed that two H-adapted strains were similar to the nonadapted strain in egg-to-adult survival but that they differed in producing adults with smaller wings. By using known relationships between wing length and reproductive potential, we found that losses in wing length underestimate losses in reproductive potential. For example, H9- and H13-adapted females had 9 and 3% wing losses, respectively, but they were estimated to have 32 and 12% losses in egg production. Fitness costs of adaptation will be investigated further via selection experiments comparing Avirulence allele frequencies for Hessian fly populations exposed or not exposed to H genes.     

Detection of the solanum fruit fly, Bactrocera latifrons (Hendel) in Tanzania (Dipt., Tephritidae)

Abstract:  The presence of the Solanum fruit fly, Bactrocera latifrons , in Africa is reported for the first time, based on trapped and reared specimens in Tanzania. Two new host records, Solanum aethiopicum and Solanum macrocarpon , are reported.     

Temperature-dependent post-diapause development and prediction of spring emergence of the pine needle gall midge (Dipt., Cecidomyiidae)

Abstract:  We determined the influence of temperature on post-diapause development of overwintered Thecodiplosis japonensis Uchida et Inouye (Dipt., Cecidomyiidae) under various treatments (12, 15, 18, 21, 24, 27 and 30°C) in an effort to predict its spring emergence. Survival and developmental period for the overwintered larvae and pupae were significantly influenced by temperature. Linear and nonlinear regression models quantitatively described temperature-dependent development and survival of T. japonensis . The survival models exhibited right-skewed bell shape patterns for all stages, indicating a more detrimental impact on survival at high temperatures. Theoretical optimum temperatures with highest survival were 22.3, 24.0 and 24.0°C for the overwintered larvae, pupae and total post-diapause development (the larvae to adults) respectively. Pupal mortality was higher at all temperatures than larval mortality and the suitable range of temperature for pupae was narrower than that of larvae. The nonlinear Briere model estimated that optimum temperatures with the fastest development were 29.1°C for larvae, 27.6°C for pupae and 27.0°C for larvae to adults. In a linear model, the lower threshold temperatures were 5.1, 7.1 and 5.9°C for larvae, pupae, and larvae to adults respectively. A predictive degree-day model was developed using trap catches of T. japonensis adult emergence during 1991–1995. The model accounted for 84.6% of year-to-year variation in adult emergence and predicted accurately the median emergence time in 1996.     

Distribution of infestation by lentil gall midge Contarinia lentis (Dipt., Cecidomyiidae) in lentil fields: statistical model

The horizontal distribution of infestation by Contarinia lentis in lentil fields, not subjected to chemical control was recorded and analysed in Slovak Republic during outbreaks of this pest in 1986–89. Infestation level was defined as the percentage of galls form the total number of galls, pods, and flowers. The highest level of infestation were found along the edges and the lowest levels in the centres of fields. The distribution of the infestation between the edge and the centre has been described for 18 fields using a nonlinear function containing two parameters. The first parameter represents the infestation level at the edge. The second parameter represents the rate of decreas of infestation from the edge towards the centre of the field. The relationship between the first parameter and the distance to the adult midge emerge site and the relationship between second parameter and the mean velocity of winds caryring females from the emergence site is described using exponential functions. The results indicate that (1) the longer the distance to the midge emergence site, the lower the infestation at the edge; and (2) the gretaer the wind velocity, the weaker the decrese in infestation from the edge towards the centre of a field.     

Revisiting within-tree trap positioning for apple maggot fly (Dipt., Tephritidae) behavioural control

Abstract:  Aiming to minimize visual competition between large red apples and red sphere traps from influencing effectiveness of traps for apple maggot fly (AMF) control, we compared AMF captures by red spheres in standard recommended position (no fruit within 15 cm), red spheres in similar position but with all fruit removed within a 30-cm radius (fruitless), red spheres with additional visual competition provided by three plastic red spheres hung 15 cm from sphere traps, and yellow panels. Traps were coated with adhesive, baited with synthetic fruit odour, and hung on trees of an apple cultivar bearing red fruit (Akeene) and trees of an apple cultivar bearing pale yellow fruit (Golden Delicious). On Akeene trees, red spheres in recommended position and fruitless red spheres caught more AMF than red spheres surrounded by plastic spheres and than yellow panels. Towards harvest, effectiveness of red spheres in recommended position decreased as reflectance of the surface of Akeene apples approached that of red spheres. By contrast, effectiveness of fruitless spheres increased over time. On Golden Delicious trees, fruitless spheres were the most effective, followed by spheres surrounded by uncoated plastic spheres and red spheres in recommended position. We conclude that removing all fruit within a 30-cm radius around red sphere traps results in similar or increased trap effectiveness relative to red spheres in recommended position.     

Genotypic interaction between resistance genes in wheat and virulence genes in the Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae)

The genotypic interaction between wheat resistance genes H3, H6, H7H8, H9 and virulence genes vH3, vH6, vH7vH8, vH9 of Hessian fly, Mayetiola destructor (Say), was studied in a growth chamber. Results showed that plants homozygous and heterozygous for the H3 gene expressed a high level of resistance against homozygous avirulent and heterozygous larvae carrying the vH3 virulence allele. The H7H8 genes were highly effective in the homozygous condition, but displayed a reduced level of resistance in the heterozygous condition. The H6 and H9 genes showed different levels of resistance against the reciprocal heterozygous larvae (vH6(a)vH6(A) versus vH6(A)vH6(a) and vH9(a)vH9(A) versus vH9(A)vH9(a)). Adults reared from vH6(a)vH6(A) and vH9(a)vH9(A) larvae were all males, consistent with the vH6 and vH9 X-linkage. Plants homozygous for H3, H6, H7H8, and H9 allowed for greater larval survival of heterozygous larvae, which suggests that avirulence to these resistance genes is incompletely dominant. Greater survival of homozygous avirulent larvae on heterozygous plants (H3h3, H6h6, H7h7H8h8, H9h9) suggests incomplete dominance of these wheat genes. Survival of heterozygous along with homozygous virulent larvae would reduce selection pressure for virulence in Hessian fly populations infesting fields of resistant wheat cultivars. This would be expected to slow the increase in frequency of virulence alleles that often results from deployment of resistant cultivars.     

Uptake of adhesive powders from lure stations by Mediterranean fruit fly (Dipt., Tephritidae)

Powders that are capable of adhering to insect cuticles can act as carrier particles when combined with insecticides, entomopathogens, or pheromones, for targeted insect control. One potential method of delivering the powder to an insect is to lure the insects to stations containing powder using a species‐specific attractant. Here, we report on the uptake of two different powders from lure stations (henceforth called ‘dispensers’) by the Mediterranean fruit fly, Ceratitis capitata, and the transfer of the powders to conspecifics during field studies in Portugal, as part of a research programme to develop lure‐and‐kill technologies based on adhesive powder. Uptake of an electrostatic wax powder, Entostat?, from dispensers was greater than uptake of a proprietary metallic powder, Entomag?, for both wild male C. capitata visiting field‐placed dispensers and laboratory‐reared males confined with dispensers in field cages. In agreement with field data, C. capitata also took up more Entostat than Entomag when artificially dosed on dispenser trays containing powder in the laboratory, and the quantities taken up were shown to be greater than that calculated from field experiments. Increasing the amount of Entostat powder in field‐placed dispensers resulted in greater uptake of powder by visiting male C. capitata. Laboratory‐reared male and female C. capitata were released in field cages in which were hung dispensers containing adhesive powder that were baited with the male attractant trimedlure. After 24 h, the powder was successfully extracted from all males and nearly all females collected, indicating that males probably transferred powder to conspecific females after visiting dispensers. The results underscore that a lure‐and‐kill system based on adhesive powder might have potential for controlling Mediterranean fruit fly and other flying insects.     

Changes in phytohormones and fatty acids in wheat and rice seedlings in response to Hessian fly (Diptera: Cecidomyiidae) infestation

Phytohormones and fatty acids (FAs) play important roles in plant resistance to insects and pathogens. In this study, we investigated the similarities and differences in the accumulations of phytohormones and FAs in the resistant wheat (Triticum aestivum L.) 'Molly' and the nonhost rice (Oryza sativa L.) 'Niponbare' in responses to Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), larval attacks. Using chemical ionization-gas-chromatography/mass spectrometry, we analyzed the concentrations of 13 phytohomones and FAs at the attack site of wheat and rice plants at 1, 6, 24, or 48 h after the initial attack. Hessian fly attack resulted in increases of salicylic acid (SA), 12-oxo-phytodienoic acid (OPDA), palmitic acid (FA16:0), but a decrease of abscisic acid in both wheat and rice plants. In addition, the accumulation of jasmonic acid (JA) increased, whereas the accumulation of cinnamic acid (CA) decreased in wheat plants, but no changes were observed in the accumulation of JA, and the accumulation of CA increased in rice plants after Hessian fly attack. However, the accumulations of benzoic acid, strearic acid (FA18:0), and oleic acid (FA18:1) increased in rice plants, but no changes were observed in wheat plants after Hessian fly attack. Hessian fly-induced changes were more rapid in wheat plants in comparison with those in rice plants. Our study suggests that SA and OPDA may be involved in resistance of wheat and rice plants to Hessian fly and that the R gene-mediated resistance responses are more rapid than nonhost resistance responses.     

Virulence in Hessian fly (Diptera: Cecidomyiidae) field collections from the southeastern United States to 21 resistance genes in wheat

Genetic resistance in wheat, Triticum aestivum L., is the most efficacious method for control of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). However, because of the appearance of new genotypes (biotypes) in response to deployment of resistance, field collections of Hessian fly need to be evaluated on a regular basis to provide breeders and producers information on the efficacy of resistance (R) genes with respect to the genotype composition of Hessian fly in regional areas. We report here on the efficacy of 21 R genes in wheat to field collections of Hessian fly from the southeastern United States. Results documented that of the 21 R genes evaluated only five would provide effective protection of wheat from Hessian fly in the southeastern United States. These genes were H12, H18, H24, H25, and H26. Although not all of the 33 identified R genes were evaluated in the current study, these results indicate that identified genetic resistance to protect wheat from Hessian attack in the southeastern United States is a limited resource. Historically, R genes for Hessian fly resistance in wheat have been deployed as single gene releases. Although this strategy has been successful in the past, we recommend that in the future deployment of combinations of highly effective previously undeployed genes, such as H24 and H26, be considered. Our study also highlights the need to identify new and effective sources of resistance in wheat to Hessian fly if genetic resistance is to continue as a viable option for protection of wheat in the southeastern United States.     

Parasitoids of Apiomyia bergenstammi (Wachtl) (Dipt., Cecidomyiidae), a new pest on pears, in Hatay province, Turkey

Abstract:  Studies were carried out on the galls formed by Apiomyia bergenstammi (Wa.) on buds and/or twigs of pear trees, in Yayladagi, Senköy, and Belen, Hatay province, Turkey in 2003. The pest was introduced into Hatay province at least 5 years ago. It produces one generation a year and hibernates as larvae in the galls. In Yayladagi, Senköy and Belen, 20, 18 and 5%, respectively, of buds/twigs of pear trees were attacked by A. bergenstammi . Each of the galls contained on average 9.6 ± 0.5 (range: 6–11) larval chambers. Adults were reared from galls collected at the beginning of spring, viz. A. bergenstammi emerged in the first half of April 2003, Oxyglypta rugosa Ruschka (Hym., Pteromalidae) and Torymus apiomyiae Boucek & Mihajlovic (Hym., Torymidae) (a new record for Turkey) emerged in the second half of April. Other chambers contained unemerged adults of Platygaster sp. (Hym., Platygasteridae). Natural parasitism rates obtained by dissecting 10 galls from Yayladagi and Senkoy in 2003 were: 26.6 ± 4.4% by O. rugosa and 10.0 ± 3.2% by Platygaster sp. The parasitism rate by T. apiomyiae was 16.6% as determined from the galls collected from Belen.