Searching for pheromone strains in the pecan nut casebearer

The pecan nut casebearer, Acrobasis nuxvorella Nuenzig (Lepidoptera: Pyralidae), is the most damaging insect pest of pecan, Carya illinoinensis (Wang) K. Koch (Juglandaceae), in the USA and Mexico. A pheromone monitoring program for A. nuxvorella has been developed to assist pecan growers in the timing of insecticide applications. The discovery that there are two pheromone types produced by A. nuxvorella has led to complications in the implementation of pheromone monitoring programs. One pheromone (referred to as standard) is attractive to moths in the southern USA, but not in Mexico. The other pheromone (referred to as Mexican) is attractive to moths in the southern USA and in Mexico. Because most male lepidopterans respond only to a specific pheromone, it was suspected that there were two pheromone strains of A. nuxvorella, one exclusively present in the northern distribution of A. nuxvorella (USA strain) and the other widely distributed from Sonora, Chihuahua, and Durango in northern Mexico to Texas, Georgia, and Oklahoma in the USA (Mexican strain). The goal of this research was to determine whether differences in pheromone response are sufficient to genetically isolate A. nuxvorella into pheromone strains. To confirm the existence of the two alleged pheromone strains, amplified fragment length polymorphism (AFLP) markers were obtained and analyzed. Four primer combinations were used to obtain a total of 483 polymorphic AFLP markers. Our results indicated that the standard and Mexican pheromones did not group A. nuxvorella into pheromone strains. However, three genetically distinct populations of A. nuxvorella were identified. Two of those three populations are sympatric throughout the southern USA and one is allopatric relative to the other two and occurs exclusively in pecan growing regions of Mexico.     

Relative abundance and flight phenology of two pheromone types of Acrobasis nuxvorella (Lepidoptera: Pyralidae)

Two synthetic sex pheromones have been developed and are currently used to detect the flight of the pecan nut casebearer, Acrobasis nuxvorella Neunzig, the most damaging pest of pecan [Carya illinoinensis (Wangenh.) K. Koch]. One pheromone (referred to as standard) is attractive to moths in the southern United States, but not in Mexico. The other pheromone (referred to as Mexican) is attractive to moths in the southern United States and in Mexico. These two pheromones have been implemented by producers as an important tool in monitoring the activity of this pest and have allowed for more efficient pesticide use. In the future, these pheromones could be used as a means of population reduction through pheromone based control methods. Trapping data taken over a 3-yr period were used to determine if phenological differences exist between pheromone types of pecan nut casebearer. The relative abundance of each pheromone type at several locations in the United States also was evaluated. Results of this study indicate that no phenological differences exist between the two pheromone types studied in the United States and that significantly more males are attracted to field-deployed pheromone traps baited with the standard pheromone than to traps baited with the Mexican pheromone.     

Environmental suitability for Agrilus auroguttatus (Coleoptera: Buprestidae) in Mexico using MaxEnt and database records of four Quercus (Fagaceae) species

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The potential global distribution of the Bronze bug Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae)

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Sequence data reflect the introduction pathways of the Sirex woodwasp parasitoid,Ibalia leucospoides (Ibaliidae,Hymenoptera)

1. The parasitoid wasp Ibalia leucospoides is native to the northern hemisphere and has been introduced to the southern hemisphere as a biological control agent for the invasive woodwasp Sirex noctilio. Two subspecies of the parasitoid, Ibalia leucospoides leucospoides (Palearctic distribution) and Ibalia leucospoides ensiger (Nearctic distribution), were introduced and are reported to have hybridized.
2. Despite extensive records of the numbers and origins of the wasps imported into the southern hemisphere, nothing is known regarding their current population diversity. We investigated the genetic variation of I. leucospoides in its native and introduced ranges using mitochondrial (COI) and nuclear (ITS) markers.
3. Mitochondrial DNA diversity in the introduced range was limited, with only five haplotypes, although sequence divergence between these haplotypes was high. Similarly, the ITS rDNA sequences revealed multiple clades present in the introduced range.
4. These results reflect introductions from a wide geographical range but where genetic bottlenecks have possibly reduced the genetic diversity. The data further reflect the origin of the I. leucospoides populations in South America and South Africa from New Zealand or Australia. We found no evidence of hybridization between the two subspecies of the parasitoid in its introduced range, and no evidence that I. leucospoides ensiger has established outside its native range.

     

The mango seed weevil Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) is characterized by low genetic diversity and lack of genetic structure

1. The mango seed weevil Sternochetus mangiferae (Fabricius) is distributed across the major mango-producing areas of the world and causes significant economic losses of mango fruit. Despite its importance as a crop pest, we have only limited information on the population genetics of the mango seed weevil.
2. Here, we examined the genetic diversity of this important pest using specimens intercepted by Beijing Customs District P. R. in China from 41 countries and regions. We used segments of the mitochondrial gene cytochrome c oxidase subunit I and the nuclear gene elongation factor 1-alpha to examine population genetic structure in this species.
3. Our results showed that genetic diversity is low in S. mangiferae, with a mean genetic distance of 0.095–0.14%. Other population genetic parameters also indicated a low level of genetic diversity among samples from a large geographic range. Analysis of molecular variance revealed little population genetic structure, and mismatch distribution analyses provided evidence of a population expansion, although other demographic metrics of population expansion were nonsignificant.
4. We suggest that the observed low level of genetic diversity and population genetic structure in S. mangiferae supports the hypothesis that the population genetics of this species has been impacted by anthropogenic transportation of mangoes and weevils.

     

Analysis of population genetic structure of two closely related tortricid species of economic importance on macadamias and litchis in South Africa

Abstract

• 1 The macadamia nut borer Thaumatotibia (Cryptophlebia) batrachopa and the litchi moth Cryptophlebia peltastica are Afrotropical species causing extensive damage to cultivated macadamias and litchis in the northernmost provinces in South Africa. Cryptophlebia peltastica also occurs as natural populations throughout the country.
• 2 To analyse the population genetic structure of the two species, amplified fragment length polymorphism analysis was conducted. Patterns of genetic diversity in C. peltastica populations in the Mpumalanga province, where the species is controlled, were compared with those in the Western Cape, where populations occur under natural conditions.
• 3 Gene diversity was high within T. batrachopa populations (H = 0.2219) with significant genetic differentiation among populations (G_st = 0.358). Cluster analysis showed that geographical populations were closely related and extensive divergence was found over local scales.
• 4 Similar to that of T. batrachopa, genetic diversity and population differentiation was high within both C. peltastica Mpumalanga and Western Cape populations (H = 0.1906 and 0.1687 and G_st = 0.4124 and 0.3799, respectively).
• 5 It is suggested that the population genetic structure of both species is influenced by their limited ability to disperse. In addition, chemical control of C. peltastica in the Mpumalanga province has not succeeded in reducing the population size, but the C. peltastica population subdivision in the Western Cape may be influenced by the limited distribution of host plants in this region.

     

Population genetic structure of Zeugodacus tau species complex in Thailand

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Genetic diversity of aboriginal and invasive populations of four‐eyed fir bark beetle Polygraphus proximus Blandford (Coleoptera,Curculionidae, Scolytinae)

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Genetic patterns and changes in availability of suitable habitat support a colonisation history of a North American perennial plant

• Climatic fluctuations during the Pleistocene influenced the geographical distribution of plant species across the southern region of California. Following an integrative approach, we combined genetic data analysis with Environmental Niche Models (ENMs) to assess the historical range expansion of Yucca schidigera, a long‐lived desert perennial native of the Baja California Peninsula.
• We genotyped 240 individuals with seven nuclear microsatellite to investigate genetic diversity distribution across 13 populations. Indeed, we used Environmental Niche Models to examine the changes on the distribution of suitable climatic conditions for this species during the LIG (~120 ka), LGM (~22 ka) and Mid Holocene (~6 ka).
• We detected high genetic diversity across Y. schidigera populations (A_R = 9.94 ± 0.38 SE; H_exp = 0.791 ± 0.011 SE) with genetic variation decreasing significantly with latitude (allelic richness: R ² = 0.38, P = 0.023; expected heterocigosity: R² = 0.32, P = 0.042). We observed low, but significant genetic differentiation (F_ST = 0.0678; P < 0.001) which was consistent with the parapatric distribution of the three genetic groupings detected by the Bayesian clustering algorithm. The ENMs suggest that suitable habitat for this species increased since the LGM.
• Our results support a range expansion of Y. schidigera across northwestern Baja California during the late Quaternary. Genetic data suggest that colonization of the current distribution followed a southward directionality as suitable climatic conditions became widely available in this region. High genetic variation across our sample suggests large historic effective population sizes for this section of the geographical range.

     

Risk assessment of Hass avocado and Mexican Lauraceae for attack by redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae)

1. The redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), vectors the mycopathogen that causes laurel wilt, a lethal vascular disease of trees in the Lauraceae. Since being detected in Georgia, USA in 2002, this invasive pest has become established in 11 additional states.
2. With continued spread, X. glabratus will likely enter Mexico. In advance of this event, this study was initiated to assess the risk posed to eight native laurels and Hass avocados, the predominant cultivar grown in Mexico.
3. Wood bolts from each species were used in (a) field tests to determine the relative attraction of female X. glabratus, (b) laboratory bioassays to evaluate boring preferences, and (c) GC–MS analyses to identify host kairomones. For comparison, tests included control bolt treatments consisting of silkbay (an attractive U.S. laurel) and Simmonds avocado (a Florida cultivar susceptible to laurel wilt).
4. Hass avocado and two native laurels (Persea schiedeana and Ocotea heribertoi vel aff.) were highly attractive to females and elicited strong boring responses. These species were high in sesquiterpene hydrocarbons, including α-copaene and α-cubebene.
5. Results of this study suggest that X. glabratus could become a serious agricultural and forest pest upon incursion into Mexico, with severe economic and ecological impacts.

     

Sodium sulfate exposure slows growth of native pecan seedlings

Pecan [Carya illinoensis (Wanngenh) K. Koch] is one of the most important nut crops in arid and semiarid regions of Mexico. Here, most pecans are grown in saline soils having poor permeability which are further degraded by the use of low-quality irrigation water. Salinity adversely affects both pecan nut quality and yield. Little work has been done to explore the physiological effects of salinity on native pecan trees. Here we examine physiological changes determined by exposure of pecan seedlings to sodium sulfate (Na₂SO₄) at four concentrations: 1000, 2000, 3000 and 4000 mg/L applied twice weekly over a 70 d period. Control plants were similarly irrigated but with water free of Na₂SO₄. The aim was to identify and quantify the putative salinity damage to native pecan seedlings growing in Chihuahua, Mexico. Seedlings exposed to Na₂SO₄ were of reduced height and stem diameter. At the highest exposure level (4000 mg/L), proline concentration in the leaflets was 820% higher (2.63 mg/g) than in the controls (0.32 mg/g), and chlorophyll was 35% lower (23.4 mg/L) than in the controls (36 mg/L). Meanwhile, sulfate ion concentration was increased by 104% from 84.47 to 172.5 mg/g. Root biomass decreased by 310% (from 30.5 to 9.5 g) and foliar biomass decreased by 260% (from 26.7 to 10 g). No disease symptoms were apparent in any seedlings suggesting that these changes were induced by Na₂SO₄ stress alone. Of the physiological parameters measured, proline, chlorophyll and sulfate ion concentration, as well as root and shoot biomasses were strongly affected by irrigation with Na₂SO₄ at concentrations of 2000 mg/L and above.     

Evidence of interaction between Sirex noctilio and other species inhabiting the bole of Pinus

• 1 Sirex noctilio is a woodwasp native to Eurasia and Northern Africa and has recently been found infesting pines in eastern North America. Its pest status in this new range is not yet known, although it is an important pest in other areas where it has been introduced. Pinus spp. in North America are hosts to several native and alien species of subcortical insects. Interactions between the woodwasp and these species may influence its distribution or the characteristics of its life history, thus affecting its population dynamics over time.
• 2 Sixty S. noctilio‐infested Pinus spp. were felled in Ontario, Canada, and all phloem‐feeding and woodboring insects were collected and identified from each 1‐m section of the tree.
• 3 Sirex noctilio was in a tree alone 10% of the time but commonly shared the tree with subcortical beetles, such as Tomicus piniperda, Pissodes nemorensis, Ips grandicollis, Gnathotrichus materiarius and Monochamus carolinensis. The woodwasp was distributed throughout the tree stem and this distribution overlapped with that of the beetles.
• 4 Fewer but larger S. noctilio males emerged from trees with beetles compared with those without, although there was no statistical difference in females.
• 5 These findings suggest that co‐habiting beetles could negatively affect S. noctilio population dynamics over time. The potential mechanisms for this interaction are discussed.

     

Niche conservatism and the potential for the crayfish Procambarus clarkii to invade South America

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Species status and population structure of the Australian Eucalyptus pest Paropsis atomaria Olivier (Coleoptera: Chrysomelidae)

1 Paropsis atomaria Olivier represents an emergent pest of Eucalyptus plantations in Queensland and New South Wales, Australia. Most prior studies on the biology and control of P. atomaria have centred on populations from Canberra in the Australian Capital Territory, but the biological relationship between beetles from Canberra and those from up to 1500 km further north are unknown. 2 DNA markers were used to determine whether P. atomaria from Canberra are the same biological species as those from Eucalyptus forestry plantations in northern New South Wales and Queensland, where the beetle has become an important pest. Using the mitochondrial gene, cytochrome c oxidase I (COI), individuals collected from across the distribution of P. atomaria were investigated for haplotype diversity and levels of mitochondrial divergence. 3 Within P. atomaria, genetic distance averaged 0.5% across 23 unique haplotypes for 93 individuals, with an average of 14% difference between P. atomaria and the outgroup species, Paropsis obsoleta. Significant genetic structure was observed relative to geographical distribution, but not with respect to host plant species of origin. Greatest divergence was between the southern‐most sample site (Canberra) and northern sites in New South Wales and Queensland, indicating reduced gene flow between these regions. 4 Individuals from across eastern Australia belong to the same genetic species with population substructuring evident. Consequently, there is no evidence to suggest cryptic species complexes exist within the currently defined taxon. Continued implementation of control strategies for P. atomaria across its distribution is appropriate.     

Microsatellite variation in Helicoverpa gelotopoeon (Lepidoptera: Noctuidae) populations from Argentina

1. Helicoverpa gelotopoeon (Dyar) (Lepidoptera: Noctuidae) is a polyphagous pest that has been reported causing damage in many agricultural crops such as soybean, chickpea and cotton. This species, together with Helicoverpa zea (Boddie), Helicoverpa armigera (Hübner) and Chloridea virescens (Fabricius), belongs to the Heliothinae complex of economic importance in Northwestern Argentina.
2. Many species in the Heliothinae subfamily have developed resistance to insecticides and insecticidal proteins from Bacillus thuringiensis (Bt). Managing resistance to these control tactics in H. gelotopoeon is of high importance and dependant on knowledge of population genetics of this species.
3. The objective of this study was to evaluate the genetic variability and structure of H. gelotopoeon populations from different host plants and geographic regions of Argentina. Towards this goal, six microsatellite loci were screened across 196 individuals.
4. The results obtained revealed high genetic diversity and lack of clear structure among the populations of H. gelotopoeon studied. This genetic homogeneity between populations from different geographical regions and hosts could be attributed to the long-range migratory capacity of Heliothinae and the generalist behaviour of H. gelotopoeon.

     

Genetic structure of cherry fruit fly (Rhagoletis cingulata) populations across managed,unmanaged, and natural habitats

The cherry fruit fly (CFF), Rhagoletis cingulata Loew (Diptera: Tephritidae: Trypetini), is endemic to eastern North America and Mexico, where its primary native host is black cherry [Prunus serotina Ehrh. (Rosaceae)]. Cherry fruit fly is also a major economic pest of the fruit of cultivated sweet (Prunus avium L.) and tart (Prunus cerasus L.) cherries. Adult CFF that attack wild black cherry and introduced, domesticated cherries in commercial and abandoned orchards are active at different times of the summer, potentially generating allochronic isolation that could genetically differentiate native from sweet and tart CFF populations. Here, we test for host‐related genetic differences among CFF populations in Michigan attacking cherries in managed, unmanaged, and native habitats by scoring flies for 10 microsatellite loci. Little evidence for genetic differentiation was found across the three habitats or between the northern and southern Michigan CFF populations surveyed in the study. Local gene flow between native black cherry, commercial, and abandoned orchards may therefore be sufficient to overcome seasonal differences in adult CFF activity and prevent differentiation for microsatellites not directly associated with (tightly linked to) genes affecting eclosion time. The results do not support the existence of host‐associated races in CFF and imply that flies attacking native, managed, and unmanaged cherries should be considered to represent a single population for pest management purposes.     

High genetic diversity and low structure in an endemic long-lived tree,Yucca capensis (Asparagaceae)

• Endemic species distributed in fragmented habitats are highly vulnerable to extinction because they may have low genetic diversity. However, some life-history traits can mitigate the effect of genetic drift on populations. We analysed the level and distribution of genetic variation and ancestral population size of Yucca capensis, a long-lived endemic plant of the Baja California Peninsula, Mexico. Its populations are scattered across a habitat that is suffering accelerated transformation.
• We used six nuclear microsatellites to genotype 224 individuals from 17 locations across the entire species' geographic range. We estimated polymorphisms, heterozygosity and genetic structure. We also evaluated the ancestral and recent effective size and time since the population started to change.
• We found high heterozygosity, high polymorphism and low differentiation among locations, suggesting a panmictic population across the range. We also detected a large ancestral effective population size, which suffered a strong reduction in the Mid-Holocene.
• Despite changes in environmental conditions caused by habitat modification, the high diversity and low differentiation in Y. capensis may result from its large ancestral effective size and life-history traits, such as plant longevity, clonal growth and mating system, which reduce the rate of loss of genetic variation. However, the dependence on a specialist pollinator that displays short flight range can reduce gene flow among the plant populations and could, shortly, lead them into an extinction vortex.

     

Uncovering the tracks of a recent and rapid invasion: the case of the fruit fly pest Bactrocera invadens (Diptera: Tephritidae) in Africa

Phytophagous insects of the genus Bactrocera are among the most economically important invasive fruit fly pests. In 2003, an unknown Bactrocera species was found in Kenya. First identified as an ‘aberrant form’ of the Asian B. dorsalis complex, it was later recognized as a new species, Bactrocera invadens. Within 2 years of its discovery, the species was recorded in several African countries, becoming an important quarantine pest. As this invasive fly was discovered only recently, no data are available on its invasion pattern in Africa. This pilot study attempts to infer from genetic data the dynamic aspects of the African invasion of this pest. Using microsatellite markers, we evaluated the level of genetic diversity and the extent of common ancestry among several African populations collected across the invaded areas. A sample from the Asian Sri Lankan population was analysed to confirm the Asian origin of this pest. Genetic data cast no doubt that Sri Lanka belongs to the native range, but only a small percentage of its genotypes can be found in Africa. African populations display relatively high levels of genetic diversity associated with limited geographical structure and no genetic footprints of bottlenecks. These features are indicative of processes of rapid population growth and expansion with possible multiple introductions. In the span of relatively few years, the African invasion registered the presence of at least two uncorrelated outbreaks, both starting from the East. The results of the analyses support that invasion started in East Africa, where B. invadens was initially isolated.     

Unravelling the global invasion routes of a worldwide invader,the red swamp crayfish (Procambarus clarkii)

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