Impact of the arundo wasp,Tetramesa romana (Hymenoptera: Eurytomidae), on biomass of the invasive weed,Arundo donax (Poaceae: Arundinoideae), and on revegetation of riparian habitat along the Rio Grande in Texas

An invasive grass, Arundo donax, occupies thousands of hectares of arid riparian habitat along the Rio Grande in Texas and Mexico, and has negative impacts on national security, water resources, and riparian ecosystems. The shoot-tip-galling wasp Tetramesa romana was released in 2009 between Brownsville and Del Rio, Texas, and has dispersed over 800?km along the river channel. Plots along the river were surveyed for shoot counts of arundo and all other plant species in 2016 at seven sites in regions in which prior studies had documented a 22% decline in arundo biomass (estimated from live shoot length) from 2007 to 2014. Estimated live biomass declined a further 32% between 2014 and 2016. Native plants accounted for 86% of the 44 species encountered in plots. Individual plots averaged five plant species, and arundo was most abundant in only 9 of 21 plots. Arundo live biomass and shoot density were negatively associated with plant diversity, indicating that live arundo interferes with germination and/or survival of other plant species. The proportion of dead shoots in plots, proportion of wasp-galled shoots, and density of exit holes made by emerging adult wasps per metre live main shoot length were positively associated with plant diversity in a combined model. Regressions indicated that the effects of wasp damage measures on diversity were mediated through their effects on main shoot mortality. By reducing live arundo biomass, the arundo wasp is fostering recovery of native plant communities at riparian sites along the Rio Grande.     

Effect of water deficit on generation time and reproduction of the gall wasp Tetramesa romana,a biological control agent of giant reed (Arundo donax)

Water deficit stress can reduce the reproductive performance of galling insects, but has not previously been studied in the context of mass-rearing of a galling agent on a perennial grass. The effects of water deficit were examined for the wasp Tetramesa romana Walker (Hymenoptera: Eurytomidae), released in the Lower Rio Grande Basin of Texas and Mexico in 2009 and in northern California in 2010 for control of giant reed (Arundo donax (L)) (Poaceae). In one study, water deficit was imposed for 7–10 weeks during gall maturation, ending when adult progeny began to emerge. Aboveground water content was reduced by 1.7% and culm height by 41% in pots receiving one-fourth of normal watering (soil saturation), indicating that water deficit stress occurred. Water deficit did not affect proportion of culms successfully galled or number of progeny produced. However, time to first exit hole appearance was 2–4 days longer and adult wasp generation time 5–7 days longer on galls on water deficit–stressed compared to control culms, thereby reducing the wasp's intrinsic rate of increase. Water deficit imposed only during parent wasp oviposition had no effect on galling success or reproduction. Water deficit thus has a negative effect on rearing by delaying adult emergence and reducing the rate of population increase, even without affecting adult fertility. Mass-rearing should involve well-watered plants, and variable drought conditions in the field should be considered when evaluating T. romana establishment and impact.     

Effect of nitrogen fertilization on growth of Arundo donax and on rearing of a biological control agent,the shoot gall-forming wasp Tetramesa romana

The shoot tip-galling wasp Tetramesa romana Walker (Hymenoptera: Eurytomidae) has been released for biological control of giant reed or arundo (Arundo donax L.) (Poaceae), an invasive grass in the USA and Mexico. The role of urea fertilization to improve plant-based mass-rearing was examined. In a greenhouse study, rhizomes were fertilized with urea pellets at rates equivalent to 1000 kg (low), 2000 kg (moderate), and 4000 (high) kg N per ha^–1. Total nitrogen content of ungalled stems was significantly 0.60–0.65% higher under low and moderate fertilization compared to unfertilized pots, and shoot water content was elevated 3–4% at all urea levels. Moderate fertilization significantly (by 1.4-fold) increased the relative growth rate of all shoots in pots, but did not affect final dry biomass. Fertilization did not affect number and duration of probing events by females. The percentage of shoots colonized by wasps that were galled, progeny production per shoot and per female, and emergent wasp size were not affected. However, average generation time (adult to adult) of emergent wasps was 4–5 days shorter on shoots in pots under moderate and high urea fertilization. After a four-week wasp emergence period, only 3–9% of progeny remained in fertilized shoots, while 21% of progeny remained inside unfertilized shoots. In field plots, fertilization did not affect gall density per m shoot length or per female released. Urea fertilization increased the efficiency of greenhouse rearing of the arundo wasp and availability of adults for release, even without direct effects on gall production.     

Impact of the Arundo scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) on the weight of Arundo donax (Poaceae: Arundinoideae) rhizomes in Languedoc southern France and Mediterranean Spain

Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale.     

Evaluation of Spanish Arundo scale Rhizaspidiotus donacis (Hemiptera; Diaspididae) survival and fecundity on three new world genotypes of Arundo donax (Poaceae; Arundinoideae)

A pre-release evaluation of survival and fecundity of the arundo scale, Rhizaspidiotus donacis, was conducted on three invasive genotypes of the riparian weed, Arundo donax. The three A. donax genotypes were collected from Laredo, Austin and Balmorhea, TX, which represented the majority of the genotypic diversity found in Texas watersheds. Although R. donacis developed on all three genotypes of the plant, the Austin A. donax genotype, followed by the Laredo genotype, were the most suitable in terms of the size of first-generation immature and adult scale populations that developed after crawler release. Both the Laredo and Austin genotypes of A. donax are likely to be of Spanish origin and are close genetic matches with scale's original host plant genotype in Alicante, Spain. In comparison, survival was lowest on the phylogenetically distant genotype of A. donax from Balmorhea, TX. Although the population size of settled, immature second-generation scales varied in a manner similar to that of the first generation, the fecundity of isolated first-generation females was not significantly different across the three plant genotypes, suggesting that R. donacis is not a genotype specialist in terms of nutrient assimilation for reproduction. Rather, differences in genotype suitability affect rates of success of crawler settling. These results indicate that selection of scale genotype from the native range may have a moderate influence on the success of R. donacis and ultimately the biological control programme.     

The effect of the armored scale,Rhizaspidiotus donacis (Hemiptera: Diaspididae), on shoot growth of the invasive plant Arundo donax (Poaceae: Arundinoideae)

The effect of feeding by the armored scale, Rhizaspidiotus donacis (Leonardi, 1920) (Hemiptera: Diaspididae) on the growth of the plant Arundo donax L. (Poaceae) was evaluated under field conditions in its native range. The study was designed to evaluate the impact of R. donacis, a candidate agent for biological control of A. donax which is invasive in arid riparian ecosystems of the Southwestern USA and Mexico. The study was carried out at five A. donax sites in the Province of Alicante, Spain, differing in altitude and climate. At each site, 30 infested lateral shoots were selected and 15 were randomly treated monthly with imidacloprid insecticide. Shoot lengths were measured monthly over a 1-year period in a comparative growth analysis. Shoots infested with R. donacis had an over 2-fold reduced growth rate as compared to treated shoots. Growth of shoots varied by site, and the effect of R. donacis on growth was most pronounced in the late spring, when mature females produced first instar scale crawlers. The impact of R. donacis on A. donax growth under field conditions in the native range, combined with its narrow host specificity, indicate that R. donacis is a promising candidate for biological control of A. donax in North America and other areas invaded by this weed.     

Origin of the invasive Arundo donax (Poaceae): a trans-Asian expedition in herbaria

Background and Aims

The hypothesis of an ancient introduction, i.e. archaeophyte origin, is one of the most challenging questions in phylogeography. Arundo donax (Poaceae) is currently considered to be one of the worst invasive species globally, but it has also been widely utilzed by man across Eurasia for millennia. Despite a lack of phylogenetic data, recent literature has often speculated on its introduction to the Mediterranean region.

Methods

This study tests the hypothesis of its ancient introduction from Asia to the Mediterranean by using plastid DNA sequencing and morphometric analysis on 127 herbarium specimens collected across sub-tropical Eurasia. In addition, a bioclimatic species distribution model calibrated on 1221 Mediterranean localities was used to identify similar ecological niches in Asia.

Key Results

Despite analysis of several plastid DNA hypervariable sites and the identification of 13 haplotypes, A. donax was represented by a single haplotype from the Mediterranean to the Middle East. This haplotype is shared with invasive samples worldwide, and its nearest phylogenetic relatives are located in the Middle East. Morphometric data characterized this invasive clone by a robust morphotype distinguishable from all other Asian samples. The ecological niche modelling designated the southern Caspian Sea, southern Iran and the Indus Valley as the most suitable regions of origin in Asia for the invasive clone of A. donax.

Conclusions

Using an integrative approach, an ancient dispersion of this robust, polyploid and non-fruiting clone is hypothesized from the Middle East to the west, leading to its invasion throughout the Mediterranean Basin.     

Host range of the European leaf sheath mining midge,Lasioptera donacis Coutin (Diptera: Cecidomyiidae), a biological control of giant reed,Arundo donax L.

The fundamental host range of the arundo leafminer, Lasioptera donacis a candidate agent for the invasive weed, Arundo donax was evaluated. L. donacis collects and inserts spores of a saprophytic fungus, Arthrinium arundinis, during oviposition. Larvae feed and develop in the decomposing leaf sheath channel tissue. Thirty-six closely related and economic grass species along with several key habitat associates were evaluated in no-choice tests. L. donacis and its associated saprophyte completed development only on A. donax, in concurrence with published reports from its native range in Mediterranean Europe. The arundo leafminer feeding leads to premature defoliation, constituting a different mode of attack on the host plant as compared to two previously released insects, the arundo wasp and arundo scale, which feed on shoot tips and rhizomes, respectively. Defoliation of A. donax is expected to increase light penetration into stands of A. donax which increases visibility for law enforcement, reduces the survival of cattle fever ticks, and enhance recovery of the native riparian vegetation along the Rio Grande and other habitats where this weed is invasive.     

Densities of the arundo wasp,Tetramesa romana (Hymenoptera: Eurytomidae) across its native range in Mediterranean Europe and introduced ranges in North America and Africa

Tetramesa romana is a biological control agent of the giant reed, Arundo donax (Poaceae: Arundinoideae), which is an invasive weed in the riparian habitats of the Rio Grande Basin of Texas, the southwestern U.S.A. and northern Mexico. Field evaluations were conducted in the native range of T. romana in Mediterranean Europe and in the introduced ranges of Texas, California, and South Africa to compare densities of the wasp. Population densities and percentage parasitism levels for the 2017 year are compared to meteorological variables (average temperature, precipitation, and heat units). In the introduced ranges of Texas (intentional) and South Africa (adventive) T. romana population densities were 39 and 10-fold higher than in the native range, respectively. Percentage parasitism of T. romana in Texas and in the native range of Thessaloniki, Greece were 2.0% and 34.3%, respectively. Annual heat unit accumulation was 1.3–2.7-fold higher at Texas sites than at other introduced or native sites, and heat units were positively associated with exit hole counts at introduced sites. Annual precipitation was 2-fold higher at Texas and South African sites than in California and the native range sites. Favourable weather conditions and reduced parasitism in Texas along the Rio Grande, as compared to the native range, allows T. romana to reach higher population levels and cause considerable damage to A. donax.     

Host range of the European,rhizome-stem feeding scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate biological control agent for giant reed,Arundo donax (Poales: Poaceae) in North America

The armored scale Rhizaspidiotus donacis (Leornardi) was evaluated as a potential biological control agent of the invasive reed grass Arundo donax in North America. No-choice tests, native range field surveys and non-target host exposures were used to determine the fundamental host range of the scale collected from Caloma, Spain and Perpignan, France. Thirty-five species, including two genotypes of A. donax and seven ecotypes of Phragmites australis, along with closely related grasses, economic grasses and habitat associates were tested. In quarantine no-choice testing using releases of 200 crawlers per plant, normal development of R. donacis was observed on A. donax and A. formosana, with very limited survival to the adult stage on Spartina alterniflora and Leptochloa spp. In follow-up studies using 1000 crawlers per plant, 10 live adult females were found on Leptochloa virgata, and one adult female on Spartina alterniflora, but average adult female abundance per plant was (2580%) 26-times lower on L. virgata and over (39,090%) 100-times lower on S. alterniflora than on A. donax. Field surveys were conducted at five locations in Spain and France at which A. donax infested with R. donacis, co-occurred with two non-target species of concern and R. donacis was only found on A. donax. Six-month field host exposures in Spain using potted Leptochloa plants entwined with heavily infested A. donax confirmed that R. donacis is specific to Arundo under field conditions. Based on our results, the scale R. donacis appears to be specific to the genus Arundo and is unlikely to harm native or cultivated plants in the Americas.     

Host range of the leaf-tier Tentamen atrivirgulatum Metz (Lepidoptera: Gelechiidae); an unsuitable candidate for biological control of Brazilian peppertree

ABSTRACT

The life history and host range of the South American leaf-tier Tentamen atrivirgulatum Metz, 2019 (Lepidoptera: Gelechiidae) was evaluated to determine its suitability for classical biological control of invasive Brazilian peppertree, Schinus terebinthifolia, in the USA. Larvae were collected during a survey in the native range of Brazil feeding on Brazilian peppertree. A quarantine colony was established and no-choice tests were conducted to determine the host range of this species. The results of these tests indicated that the larvae fed and completed development on seven of the eleven non-target species tested. Percent survival on these non-targets ranged from 20% to 100%. Larval survival was 50% when fed the target weed Brazilian peppertree. When larvae were fed leaves of these non-targets, pupal weights were significantly lower only for those fed Pistacia chinensis. Development time to the pupal and adult stages did not differ with larval diet. These no-choice results indicate T. atrivirgulatum larvae have a broad host range and thus this species will not be developed as a biological control agent for Brazilian peppertree in the USA.     

Two-sex life table of Nasonia vitripennis (Hymenoptera: Pteromalidae) and the effects of Wolbachia on its reproduction and parasitism of Musca domestica (Diptera: Muscidae)

Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) is now emerging as genetic model organism for development and genetics research. As a parasitic insect, the egg, larval, pupal, and early adult developmental stages of N. vitripennis occur within the enclosed fly pupae, which differ a lot from the life cycle of other insects that undergo complete metamorphosis. Previous report on the life table of N. vitripennis was based on females only. In this study, the two-sex life table approach was used to examine the parasitic efficiency of N. vitripennis within the pupae of Musca domestica L. (Diptera: Muscidae), and the influence of low temperature and the endosymbiotic bacteria Wolbachia on wasp population growth were investigated. Wolbachia could improve the fecundity of N. vitripennis and prolong the host life history. We propose the preservation of M. domestica pupae at 4 °C for 15 days is suitable in practical use. Age-stage, two-sex life table analysis revealed the stage structure and variability of N. vitripennis population growth, and also provide useful information about the effects of Wolbachia on its reproduction and parasitism of M. domestica.     

Parasitisation of Tetrastichus brontispae (Hymenoptera: Eulophidae), a biological control agent of the coconut hispine beetle Brontispa longissima (Coleoptera: Chrysomelidae)

The gregarious endoparasitoids Tetrastichus brontispae Ferrière is one of the important natural enemies of the coconut hispine beetle Brontispa longissima (Gestro), a serious invasive pest on coconut palm plants (Cocos nucifera L.) in Southeast Asia. Development at different temperatures, effect of host and female ages, effect of food and oviposition frequency and superparasitism were investigated in the laboratory. Females were allowed only one attack against one host in all experiments. The wasp developed in a host between 19 and 30°C, whilst no wasp completed its immature development at 16 and 31°C. Host and female ages affected parasitisation. Parasitoid emergence was high on day 0 and day 1 pupal hosts, and younger females produced more offspring than older females. The longevity of the female was affected not only by food supply, but also by oviposition frequency. The female survived longer when oviposition frequency was low. However, the total number of hosts parasitised by the female during her lifetime did not differ at different oviposition frequencies. In superparasitism, although the percentage of adult emergence and body size of offspring decreased with an increasing number of attacks per host, a host parasitised by up to four females could produce parasitoid offspring.     

Non-selective feeding and oviposition behaviour of Cryptocephalus trifasciata (Coleoptera: Cerambycidae: Cryptocephalinae) precludes its use as a biological control agent for downy rose myrtle (Rhodomyrtus tomentosa)*

Downy rose myrtle (Rhodomyrtus tomentosa), a southeast Asian native shrub, invades natural areas in Florida and Hawaii, where it forms dense, impenetrable thickets. We tested the host affinity and survivorship of a case-bearing beetle, Cryptocephalus trifasciata on R. tomentosa and related species. C. trifasciata adults and larvae fed, oviposited and/or completed development on all non-target species tested (N?=?11). C. trifasciata has a broad host range and is unsuitable for use as a biological control agent.     

Potential impact of the native hyperparasitoid Conura albifrons (Hymenoptera: Chalcididae) on the exotic biological control agent Diadromus pulchellus (Hymenoptera: Ichneumonidae)

The solitary pupal parasitoid Diadromus pulchellus was released in 2010 as a classical biological control agent against leek moth, Acrolepiopsis assectella, an important new pest of onion crops, Allium spp. in Eastern North America. Post-release monitoring using sentinel leek moth pupae revealed that the facultative hyperparasitoid Conura albifrons was attacking leek moth and potentially D. pulchellus as well. We used laboratory choice and no-choice tests to assess the potential impact of C. albifrons on leek moth and D. pulchellus. C. albifrons is capable of developing in newly formed leek moth pupae and leek moth pupae containing first instar D. pulchellus, as well as in fully developed D. pulchellus pupae. Survivorship of both leek moth and D. pulchellus exposed to C. albifrons was significantly lower than that of unexposed controls. In choice trials, prior host experience significantly influenced host choice by C. albifrons. These results suggest that C. albifrons could impact the establishment of D. pulchellus through both competition and intraguild predation, and that the impact has the potential to change as the relative frequency of the two hosts shifts in field populations.     

Introduction,establishment, and impact of Lathrolestes thomsoni (Hymenoptera: Ichneumonidae) for biological control of the ambermarked birch leafminer,Profenusa thomsoni (Hymenoptera: Tenthredinidae), in Alaska

The ambermarked birch leafminer, Profenusa thomsoni Konow (Hymenoptera: Tenthredinidae), was first discovered in Alaska in 1991 but was not correctly identified until 1996 when it invaded Anchorage and became a widespread and damaging pest to forest and urban birches. In 2003, the parasitoid wasp, Lathrolestes thomsoni Reshchikov (Hymenoptera: Ichneumonidae), was selected as a candidate for a classical biological control program against P. thomsoni. Parasitized leafminer larvae were collected from the Northwest Territories and Alberta, Canada, where it was previously introduced and causing injury to Betula spp., and transferred to Alaska in soil as pre-pupae for emergence. From 2004 to 2008, 3636 adult L. thomsoni adults were released in birch stands in Alaska. Parasitoids were later recovered at all six release sites in Anchorage and the Kenai Peninsula. While percent leaves mined declined by 30–40% at parasitoid release sites over the period of this study, a similar decline was also observed at paired, non-release long-term monitoring sites. Therefore, the decline in the pest density cannot be ascribed entirely to L. thomsoni.     

Discovery of a CI-inducing Wolbachia and its associated fitness costs in the biological control agent Aphytis melinus DeBach (Hymenoptera: Aphelinidae)

Wolbachia is an endosymbiotic bacterium that infects a large percentage of arthropods and can affect the fitness of its host. Here we verified for the first time that the biological control agent Aphytis melinus DeBach is infected with a Wolbachia that causes complete cytoplasmic incompatibility, and conducted an insectary and field survey to determine the infection frequency. A. melinus appears to suffer fitness costs associated with infection based on measurements of longevity and fecundity. We also quantified the Wolbachia titers of A. melinus reared at different temperatures and found that, although not completely cured, increased temperature resulted in a significant reduction in the number of Wolbachia copies found in an individual wasp. Implications of our results for biological control are discussed.     

The role of augmentative releases of indigenous parasitoid Metaphycus lounsburyi (Hymenoptera: encyrtidae) in enhancing the biological control of Saissetia oleae (Homoptera: coccidae) on olive in Egypt

The Mediterranean black scale, Saissetia oleae (Olivier) (Homoptera: Coccidae) is the most important pest of olive in Egypt. Indigenous parasitoid Metaphycus lounsburyi (Howard) (Hymenoptera: Encyrtidae) from different localities in Egypt, were manipulated, reared and mass produced for classical biological control in Egypt, more than 193130 parasitoids were released. Several releases were made between May 1999 to April 2001. Increases of the parasitism from 17.4 to 42.0 and from 6.4 to 19.2 during the first year (1999–2000) and the second year (2000–2001), respectively in the Northern Coast. This parasitoid became established in some of the release sites in El-Arish and Matruh Governorates.     

Predicting the host range of Nystalea ebalea: Secondary plant chemistry and host selection by a surrogate biological control agent of Schinus terebinthifolia

The safety of weed biological control depends upon the selection and utilization of the target weed by the agent while causing minimal harm to non-target species. Selection of weed species by biological control agents is determined by the presence of behavioral cues, generally host secondary plant compounds that elicit oviposition and feeding responses. Non-target species that possess the same behavioral cues as found in the target weed may be at risk of damage by classical biological control agents. Here we conducted host range tests and examined secondary plant compounds of several test plant species. We studied the specialist herbivore Nystalea ebalea (Lepidoptera: Notodontidae) a Neotropical species, present in Florida as a surrogate biological control agent of the weed, Brazilian peppertree Schinus terebinthifolia, invasive in Florida and Hawaii. We found that the larvae had the greatest survival when fed the target weed, the Neotropical species Spondias purpurea, the Florida native species Rhus copallinum, and the ornamental Pistacia chinensis. Reduced survival and general larval performance were found on the native species Metopium toxiferum and Toxicodendron radicans. Both the volatiles and the allergen urushiols were chemically characterized for all species but urushiol diversity and concentration best predicted host range of this herbivore species. These results provide insight into host selection and utilization by one oligophagous Schinus herbivore. Other potential biological control agents may also be sensitive to plants that contain urushiols and if so, they may pose minimal risk to these native species.     

Host specificity ofAceria (Eriophyes) malherbe, [Acari: Eriophyidae], a biological control agent for the weed,Convolvulus arvensis [Convolvulaceae]

The host specificity of the gall mite,Aceria (Eriophyes) malherbe (Nalepa), from Greece was studied under quarantine conditions at Albany, California USA. Of the species, ecotypes, or strains tested, onlyConvolvulus andCalystegia spp. supported gall formation and mite reproduction. Although 2 of the native, North AmericanCalystegia species that served as laboratory hosts are threatened or endangered species,A. malherbe is considered safe for release in the USA as a biological control agent of the weed,Convolvulus arvensis (L.).