Mass rearing methods for Galerucella calmariensis and G. pusilla (Coleoptera: Chrysomelidae), biological control agents of Lythrum salicaria (Lythraceae).

Purple loosestrife, Lythrum salicaria L., an invasive Eurasian perennial, is degrading wetlands across temperate North America. Because conventional control methods have proven ineffective, current emphasis is on the introduction and release of host-specific biological control agents. To increase the availability of control agents for distribution and thus the potential for faster control, mass rearing techniques for 2 leaf beetles, Galerucella calmariensis L. and G. pusilla Duftschmidt, were developed under greenhouse and field conditions. To evaluate the success of various rearing techniques on the number of beetles produced and the effect of these methods on offspring quality, female fecundity, larval development, and adult survival were monitored. Survival of adults maintained at 4 degrees C was approximately 60% and was independent of the type of material used for storage, duration of overwintering, and number of beetles per container. Survival rates increased with increasing numbers of dry stems offered as an overwintering substrate. Females in smaller cages had significantly higher oviposition rates, and with an increase in the number of beetles per cage, female fecundity doubled. Continuous rearing in the greenhouse reduced female fecundity. Allowing beetles to overwinter significantly improved fecundity and rearing efficiency, independent of whether beetles overwintered in a controlled environment or in the field. Field rearings consistently produced 2-5 times more offspring with higher survival than greenhouse rearings.     

Feeding and oviposition rates in the pine weevil Hylobius abietis (Coleoptera: Curculionidae)

Feeding and oviposition in the pine weevil Hylobius abietis (Linnaeus) were monitored under laboratory conditions in two long-term experiments lasting over an extended breeding season. Data were also collected from weevils under semi-natural conditions outdoors. In addition, the effects of crowding and starvation were studied in separate experiments. During the main peak oviposition period, female H. abietis consumed 50% more bark tissue than males. When oviposition ceased, the feeding rate of the females declined to the same level as in the males. The rates and spatial distribution patterns of oviposition and feeding were clearly affected by climatic conditions and the degree of crowding. Females were estimated to lay on average 0.8 eggs per day during the season under outdoor conditions. The realized fecundity of a female weevil during the first season was estimated to be approximately 70 eggs. The estimated average rate of feeding was 23 mm2 of Scots pine bark per weevil per day. This implies that planted seedlings can only constitute a minor part of the food resources needed to sustain H. abietispopulations of the size that usually appear on fresh clear-cuttings in northern Europe.     

Development of a meridic diet for Hylobius transversovittatus (Coleoptera: Curculionidae) and the role of carbohydrates in feeding, growth, and survival of larvae

The root-feeding weevil Hylobius transversovittatus Goeze (Coleoptera: Curculionidae) is used for biological control of the invasive plant purple loosestrife, Luthrum salicaria L. (Lythraceae). A simple rearing system for this weevil was developed with the goals of improving production techniques and increasing the availability of insects for field introduction. Additionally, the dietary effects of digestible and indigestible carbohydrates were explored. A meridic diet for rearing H. transversovittatus was formulated through nutritional alterations of a boll weevil, Anthonomus grandis grandis Boheman, diet. Diet attractiveness was evaluated on two levels: first, by recording the incidence of initial tunneling, and second, by estimating the larval establishment rate. The performance of test diet formulations was further assessed by measuring developmental and survival rates of H. transversovittatus. Sucrose, starch, and three types of indigestible carbohydrates were tested as components to improve diet performance. Physical properties of the diet, modified by fillers in test formulations, produced major effects on the initial tunneling of hatchlings. The establishment of hatchlings was affected by chemical properties of the diet. Increases in sucrose concentration decreased larval establishment, decreased the rate of larval development, and decreased larval survival. However, omitting sucrose from the diet, or replacing it with starch, increased mortality of first instars. In advanced stages of larval development, omitting sucrose from the diet did not significantly affect larval survival. The developmental rate of larvae was increased when the amount of digestible carbohydrate was reduced. To date, seven generations of the univoltine H. transversovittatus have been successfully produced on this new meridic diet.     

Laboratory rearing method for the stem weevil,Hyperodes bonariensis (Coleoptera: Curculionidae)

The stem weevil, Hyperodes bonariensis Kuschel, was reared from egg to adult for eight generations on an artificial medium. At 26±0.5°C, 55±5% RH, and 12‐h photo‐period, development time from newly hatched larva to adult averaged about 28 days. There were four larval instars lasting about 14 days, followed by prepupal and pupal stages lasting a further 14 days. Oviposition occurred 2 weeks after adult emergence; mated females laid viable eggs. Ovarian diapause in some females was also noted. It is possible to rear about six generations a year under these conditions.     

Maturation feeding and reproductive development in adult pine weevil, Hylobius abietis (Coleoptera: Curculionidae)

Maturation feeding on conifer bark by newly emerged Hylobius abietis(Linnaeus) is essential for reproductive development. When feeding occurs on young conifer transplants, this weevil causes significant economic damage. Between emergence and oviposition however, weevils feed on bark from different sources but of unknown nutritional 'quality'. The factors influencing the rate of feeding by males and females and female reproductive development were determined in laboratory bioassays using two contrasting food sources - the bark on different species of seedling conifer and on logs of mature trees. The nutritional 'quality' of bark was characterized by the concentration of nitrogen, total sugars, total polyphenols and resin. Regression models were used to show that overall, the rate of feeding on the bark of both seedlings and logs increased with weevil size and was negatively related to nitrogen concentration. The nitrogen concentration in seedling bark (mean 1.1%) was about three times higher than that of logs (mean 0.4%). The rate of reproductive development increased with nitrogen intake during feeding and the preoviposition period for weevils feeding on seedlings and logs was ~ 13 days and 46 days, respectively. Analysis of weevil mortality and of the weight gain of surviving weevils suggests that a nitrogen content of around 0.3% may be limiting for H. abietis. The possibility that nutritionally adequate food resources may be limiting for H. abietis is briefly discussed.     

Revised methods for the mass-rearing of the spotted knapweed biological control agent,Cyphocleonus achates (Coleoptera: Curculionidae), in field corrals

Cyphocleonus achates (Fahraeus), a root-feeding weevil introduced from Eurasia, is an effective biological control agent against spotted knapweed, Centaurea stoebe L. ssp. micranthos. Because C. achates is univoltine and does not fly, distribution of the weevil has been slow. To hasten the weevil's distribution, a rearing effort using field corrals was initiated at a facility in Corvallis, Montana. Procedures for mass-rearing the weevil in field corrals are described, with an emphasis on improvements over earlier methods. The described field-corral approach is effective and appropriate for producing C. achates for distribution in the western United States.     

Field evaluation of entomopathogenic nematodes for the biological control of the annual bluegrass weevil,Listronotus maculicollis (Coleoptera: Curculionidae), in golf course turfgrass

The ability of entomopathogenic nematodes to suppress larval populations of the annual bluegrass weevil, Listronotus maculicollis, was investigated under field conditions over a 3-year period (2006–2008). Combination of nematode species, application rate and timing produced strong numerical yet few statistically significant reductions. Steinernema carpocapsae Weiser, S. feltiae Filipjev, and Heterorhabditis bacteriophora Poinar applied at 2.5×10⁹ IJs/ha reduced first generation late instars between 69 and 94% in at least one field trial. Steinernema feltiae provided a high level of control (94%) to low densities (~20 larvae per 0.09 m²), but gave inadequate control for higher densities (24 and 50% suppression). No significant differences were found among treatment timings. However, applications timed to coincide with the peak of larvae entering the soil (fourth instars) generally performed better than applications made prior to (preemptive) or after the majority of the population advanced from the fourth instar. Nematode populations declined sharply between 0 and 14 days after treatment (DAT). Although nematode populations later increased (at 28 DAT), indicating an ability to recycle within hosts in the environment, they were nearly undetectable 56 DAT when the second generation host larvae were present in the soil. Applying commercially available nematode species at standard field rates cannot reliably reduce L. maculicollis immature densities on golf courses, nor will single applications suppress multiple generations. Future research will need to identify application strategies to improve biocontrol consistency.     

Population regulation of a classical biological control agent: larval density dependence in Neochetina eichhorniae (Coleoptera: Curculionidae), a biological control agent of water hyacinth Eichhornia crassipes

The release of classical biological control agents has reduced the economic, environmental and social problems caused by water hyacinth, Eichhornia crassipes; however, additional control measures are needed in some locations. Water hyacinth plants were treated with different densities of eggs of the weevil Neochetina eichhorniae Warner, one of the main control agents, under different nutrient regimes in a controlled experiment. Plants were destructively sampled and the development of N. eichhorniae was assessed. The survival of first and second instars declined as larval density increased. Plant nutrient status did not directly affect the mortality rate of larvae, but at higher nutrient concentrations larvae developed faster and were larger at a given developmental stage. It is argued that the density dependence operating in N. eichhorniae occurs through an interaction between young larvae and leaf longevity. Consequently, events which disrupt water hyacinth leaf dynamics, e.g. frost or foliar herbicides, will have a disproportionately large effect on the control agents and may reduce the level of control of the host.     

Biology and host specificity of Ceutorhynchus scrobicollis (Curculionidae; Coleoptera), a root-crown mining weevil proposed as biological control agent against Alliaria petiolata in North America

Ceutorhynchus scrobicollis is a root-crown mining weevil proposed for release as biological control agent of Alliaria petiolata (Brassicaceae, Thlaspideae), a European biennial herb, currently invading temperate North America. Using a combination of laboratory, common garden and fieldwork we studied biology, ecology and host range of C. scrobicollis, a univoltine species that oviposits and develops in A. petiolata rosettes in fall and spring. Individual C. scrobicollis can be long-lived (>2 years) and females show a second oviposition period. Weevils did not attack any of 31 test plant species outside the Brassicaceae. Within the Brassicaceae, five species allowed complete larval development under no-choice conditions. In subsequent choice tests, three of these five species (Nasturtium officinale, Peltaria alliacea and Thlaspi arvense; which are of European origin) were attacked. North American Rorippa sinuata was the only native species to be attacked by C. scrobicollis and only under no-choice conditions. Results of subsequent impact experiments showed that C. scrobicollis attack changed plant architecture but had no effect on overall plant vigour and reproductive output of R. sinuata, suggesting lack of impact on demography or population dynamics. A petition for field release of C. scrobicollis in North America has been submitted.     

Karyological investigations on seven weevil species (Coleoptera, Curculionidae)

Karyological studies were carried out on seven Palaearctic weevils. The following chromosome numbers were found in individual species, i.e. Otiorhynchus niger (F.), Phyllobius viridearis (Laich.), Phyllobius scutellaris Redt., Phyllobius calcaratus (F.), Polydrusus cervinus (L.), and Brachyderes incanus (L.) 2n = 22, n Male = 10 + Xyp, in Lixus elegantulus (Boh.) 2n = 22, n Male = 21 + Xyp. The heterochromosomes of all the examined species form, in the first meiotic metaphase, a typical parachute bivalent.     

Entomopathogenic nematodes to control black vine weevil (Coleoptera: Curculionidae) on strawberry.

We investigated the potential of heterorhabditid nematodes to control larvae of the black vine weevil, Otiorhynchus sulcatus (F.), in 2 field experiments in commercial strawberry plantings. In both experiments, nematodes were applied directly onto the straw mulch, or onto the soil after temporary removal of the mulch. Heterorhabditis marelatus Lui & Berry (Rhabditida: Heterorhabditidae) reduced numbers of weevil larvae and the percentage of plants infested in both experiments, irrespective of straw removal. In the 1st field experiment, a sponge-packed H. marelatus formulation produced lower numbers of O. sulcatus larvae per strawberry plant (mean O. sulcatus larvae per plant = 0.7) and proportion of infested plants (42%) compared with a vermiculite formulation (mean O. sulcatus larvae per plant = 1.8, proportion infested plants 67%) and an untreated control (mean O. sulcatus larvae per plant = 1.9, proportion infested plants 75%). In the first 2 wk after application, more H. marelatus were found in soil samples collected from plots treated with sponge-packed nematodes, than from plots treated with vermiculite-formulated nematodes. In the 2nd field experiment, sponge-packed formulations of H. bacteriophora Poinar (Rhabditida: Heterorhabditidae) and H. marelatus were tested. H. marelatus caused a reduction in both numbers of weevil larvae (mean O. sulcatus larvae per plant = 0.1) and proportion of infested plants (9%) but H. bacteriophora did not (mean O. sulcatus larvae per plant = 0.45, proportion infested plants 34%). More H. bacteriophora were recovered from soil samples than H. marelatus during the first 7 d of this experiment. However, laboratory studies revealed no difference in the persistence of these 2 nematodes in sand.     

Cytogenetic investigations on seven Palaearctic weevil species (Coleoptera, Curculionidae).

Cytogenetic investigations were carried out on seven species of bisexual weevils from five subfamilies. The following numbers of chromosomes were found in individual species: 2n = 22, n male = 10 + Xyp in Ptochus porcellus Boh. (Otiorhynchinae); 2n = 40, n male = 19 + Xyp in Larinodontes turbinatus Gyll. (Cleoninae); 2n = 26, n male = 12 + Xyp in Curculio pellitus (Boh.) (Curculioninae); 2n = 30, n male = 14 + Xyp in Acalles camelus (F.), Acalles echinatus (Germ.), Acalles hypocrita Boh. (Cryptorhynchinae), and 2n = 40, n male = 19 + Xyp in Cionus hortulanus (Foucr.) (Mecininae). The heterochromosomes of all the examined species form, in the first meiotic metaphase, a parachute bivalent. The chromosome number and sex determining system of six species and two genera are described for the first time.     

Geographical distribution of the weevil subfamily Ceutorhynchinae (Coleoptera, Curculionidae)

A brief general characteristic and review of distribution of the subfamily Ceutorhynchinae over zoogeographical realms are given, with an emphasis on the distribution within the Holarctic and Palaearctic. The potential of exploiting landscapes of all natural zones of the Holarctic by a low-rank taxon is exemplified by the Holarctic Ceutorhynchus cochleariae (Gyll.) species-group comprising ca. 20 species evenly distributed between the Palaearctic and Nearctic. Although neighboring with the powerful centers of tropical biota, the Holarctic fauna of the subfamily Ceutorhynchinae is formed mostly of endemic and subendemic genera which are especially abundant in the Palaearctic. This region possesses the most diversified generic and species composition of the fauna consisting of predominantly endemic and subendemic genera (in the Mediterranean and Saharo-Gobian regions, also of the highly diversified tribe Oxyonychini) up to its southern border. The existence of characteristic transitional faunas in the zones of contact of the Holarctic fauna with the faunas of the tropical regions in East Asia and Mexico is shown. These transitional faunas include a considerable number of endemic taxa of the genus and species groups. A conspicuous feature of the Palaearctic ceutorhynchine fauna is the rather numerous complex of the upland and high-latitude species.     

Identification and biological role of the endosymbionts Wolbachia in rice water weevil (Coleoptera: Curculionidae)

Wolbachia spp. are obligate intracellular bacteria present in reproductive tissues of many arthropod species. Wolbachia infection status and roles in host reproduction were studied in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae), an introduced species in China. We examined Wolbachia infection status in five populations in China where it reproduces parthenogenetically, and one native population in Southeast Texas, where it reproduces bisexually. All populations were infected by Wolbachia, and all specimens in each population were infected by Wolbachia of a single strain. Phylogenetic analyses based on multilocus sequence typing system indicated that Wolbachia in non-native L. oryzophilus weevils diverges evidently from those in native weevils. After treatments with tetracycline, parthenogenetic weevils reduced the fecundity significantly and eggs were not viable. Our results suggest that Wolbachia are necessary for oocyte production in L oryzophilus.     

Virulence of entomopathogenic nematodes to pecan weevil larvae, Curculio caryae (Coleoptera: Curculionidae), in the laboratory

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans in the Southeast. Entomopathogenic nematodes have been shown to be pathogenic toward the larval stage of this pest. Before this research, only three species of nematodes had been tested against pecan weevil larvae. In this study, the virulence of the following nine species and 15 strains of nematodes toward fourth-instar pecan weevil was tested: Heterorhabditis bacteriophora Poinar (Baine, HP88, Oswego, NJ1, and Tf strains), H. indica Poinar, Karunakar & David (original and Homl strains), H. marelatus Liu & Berry (IN and Point Reyes strains), H. megidis Poinar, Jackson & Klein (UK211 strain), H. zealandica Poinar (NZH3 strain), Steinernema riobrave Cabanillas, Poinar & Raulston (355 strain), S. carpocapsae (Weiser) (All strain), S. feltiae (Filipjev) (SN strain), and S. glaseri (Steiner) (NJ43 strain). No significant difference in virulence was detected among nematode species or strains. Nematode-induced mortality was not significantly greater than control mortality (in any of the experiments conducted) for the following nematodes: H. bacteriophora (Baine), H. zealandica (NZH3), S. carpocapsae (All), S. feltiae (SN), S. glaseri (NJ43), and S. riobrave (355). All other nematodes caused greater mortality than the control in at least one experiment. Heterorhabditis megidis (UK211) but not H. indica (original) displayed a positive linear relationship between nematode concentration and larval mortality. Results suggested that, as pecan weevil larvae age, they may have become more resistant to infection with entomopathogenic nematodes.     

Efficacy of diatomaceous earth to control internal infestations of rice weevil and maize weevil (Coleoptera: Curculionidae)

Densities of 10, 20, and 30 hard red winter wheat kernels, Triticum aestivum L., were infested with different life stages of the rice weevil, Sitophilus oryzae (L.), mixed with 35 g of wheat treated with 300 ppm of the Protect-It (Mississauga, Ontario, Canada) formulation of diatomaceous earth (DE), and held at 22, 27, and 32 degrees C. A similar test was conducted by exposing densities of 6, 12, and 18 corn kernels infested with different life stages of the maize weevil, Sitophilus zeamais Motschulsky, mixed with 30 g of corn, Zea mays L., treated with 300 ppm of DE. Mortality of adults emerging from kernels in wheat treated with DE was always greater than controls, and ranged from 56 to 90% at 22 degrees C and was >90% at 27 and 32 degrees C. In most treatment combinations, exposure to DE suppressed F1 progeny by 60-90% relative to untreated controls. Mortality of adult maize weevils on treated corn held at 22 and 27 degrees C was lower than mortality of rice weevils on wheat, and ranged from 4 to 84%. F1 production was low in corn held at 22 degrees C, and no F1s were produced in either the controls or the treatments at 32 degrees C. In treated corn held at 27 degrees C, exposure to the DE suppressed F1 progeny by approximately 70-80% relative to the untreated controls. Results of this study show that rice weevils and maize weevils emerging from infested kernels as adults are susceptible to DE, and these results are comparable to other studies in which adult weevils were exposed directly on wheat or corn treated with DE. Although adult weevils will be killed by exposure to DE, some oviposition could still occur and progeny suppression may not be complete; however, application of DE to commodities already infested with internal feeders, such as the rice weevil and the maize weevil, could help eliminate or suppress the infestation.     

Field parasitism of nontarget weevil species (Coleoptera: Curculionidae) by the introduced biological control agent Microctonus aethiopoides Loan (Hymenoptera: Braconidae) over an altitude gradient

The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was approximately 2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.