Host plant recognition by the root feeding clover weevil, Sitona lepidus (Coleoptera: Curculionidae)

This study investigated the ability of neonatal larvae of the root-feeding weevil, Sitona lepidus Gyllenhal, to locate white clover Trifolium repens L. (Fabaceae) roots growing in soil and to distinguish them from the roots of other species of clover and a co-occurring grass species. Choice experiments used a combination of invasive techniques and the novel technique of high resolution X-ray microtomography to non-invasively track larval movement in the soil towards plant roots. Burrowing distances towards roots of different plant species were also examined. Newly hatched S. lepidus recognized T. repens roots and moved preferentially towards them when given a choice of roots of subterranean clover, Trifolium subterraneum L. (Fabaceae), strawberry clover Trifolium fragiferum L. (Fabaceae), or perennial ryegrass Lolium perenneL. (Poaceae). Larvae recognized T. repens roots, whether released in groups of five or singly, when released 25 mm (meso-scale recognition) or 60 mm (macro-scale recognition) away from plant roots. There was no statistically significant difference in movement rates of larvae.     

Behavioural Acceptability of Sitona lepidus (Coleoptera: Curculionidae) to the Parasitoid Microctonus aethiopoides (Hymenoptera: Braconidae) Using the Pathogenic Bacterium Serratia marcescens Bizio

Microctonous aethiopoides Loan has been introduced into New Zealand to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) a pest of clover ( Trifolium spp.), has recently established in New Zealand. Laboratory experiments to test the potential of M. aethiopoides to parasitize S. lepidus has resulted in very low levels of parasitism. To investigate whether there were behavioural or physiological barriers to successful parasitism, two experiments were conducted using the insect pathogenic bacterium. Serratia marcescens Bizio as a marker for parasitoid ovipositor penetration. Firstly, M. aethiopoides 'treated' with S. marcescens were exposed to weevils and rapid weevil mortality was used to indicate ovipositor penetration. Up to 50% mortality of S. lepidus occurred, which was comparable with mortality observed in the permissive host Listronotus bonariensis . Dissection of S. lepidus exposed to parasitoids treated with distilled water showed that ca. 21% contained parasitoid eggs of which 98% were nonviable. In the second experiment, exposure periods of 24, 48 and 72 h to S. marcescens -treated parasitoids produced an increase in S. lepidus mortality of 14, 28 and 38%, respectively. There was 3% successful parasitoid development in weevils exposed for 72 h to parasitoids treated with distilled water. M. aethiopoides has been shown to develop successfully in a wide range of non-target weevil species both in the laboratory and field. Possible reasons for poor survival of M. aethiopoides immature stages in S. lepidus are discussed.     

Studies on the dispersal and migration of Sitona regensteinensis (Coleoptera: Curculionidae)

Sitona regensteinensis is dimorphic, with a brachypterous non-migratory form and a macropterous obligatory migratory form, existing in the ratio of 9 : 1 respectively. Three types of movements are involved in the dispersal of the beetle. The flight of the macropterous form leads to migration; the brachypterous adults disperse by walking when they emerge from hibernation in spring; but this causes only short range dispersal in contrast to the migratory flights of the macropterous individuals. Both forms move from the hostplant to the soil and back, depending on the weather, particularly the temperature. The migratory form is almost devoid of flight muscles when it emerges from pupation. The flight muscles grow during the autumn feeding period and remain unchanged through the winter until flight occurs during spring. Compared with the non-migratory form, the growth of the ovary and egg-production of the migratory form is retarded during the flight period.

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Zusammenfassung Sitona regensteinensis ist univoltin und dimorph, mit einer kurzflügeligen, nicht wandernden und einer macropteren, wandernden Form. Die brachypteren und macropteren Formen treten im Verhältnis 9 : 1 auf. Drei Fortbewegungsarten sind mit der Ausbreitung der erwachsenen Käfer verknüpft. Eine ist die Ausbreitung der vollflügeligen Individuen durch Flug, der alljährlich zur Migration führt. Die Ausbreitung der kurzflügeligen Käfer durch Lauf bald nach dem Verlassen des Winterlagers ist der zweite Typ. Diese Fortbewegungsart führt zur Ausbreitung der erwachsenen Käfer auf die Wirtspflanzen der Nachbarschaft, ist aber keine migratorische Ortsveränderung im heutigen Sinn. Drittens erfolgen Bewegungen beider Formen von Sitona vom Erdboden zur Wirtspflanze und zurück. Diese Bewegungen werden von den Boden- und Lufttemperaturen beherrscht und hängen aufs engste mit den Änderungen des Wetters während Herbst, Winter und Frühling zusammen. Es wurden bei den dimorphen Formen auch Unterschiede im Ablauf der Ovarienreife sowie der Eiproduktion festgestellt. Das Wachstum der Ovarien und die Eiproduktion der macropteren Form wird um einige Wochen verzögert, während der die Wanderflüge auftreten. Die Migrationszeit ist festgelegt und kurz. Sie ist auf den letzten Teil des Frühjahrs beschränkt. Die jahreszeitlichen Veränderungen der Flugmuskulatur der macropteren Form wurden quantitativ untersucht. Es wurde festgestellt, daß die Muskeln zur Zeit des Verlassens der Puppen unentwickelt sind. Sie wachsen während der Fraßperiode im Herbst heran und bleiben den Winter über unverändert erhalten. Diese Ergebnisse liefern Hinweise zur Unterstützung einiger der derzeitigen Vorstellungen über die Migration der Insekten.

     

Studies on the feeding of Sitona lineatus L. (Coleoptera: Curculionidae) on white clover (Trifolium repens L.) seedlings

Measurements of feeding damage by sitona weevil (Sitona lineatus L.) adults on differing numbers of seedlings of white clover (Trifolium repens L.) at the first and fourth trifoliate leaf stage were made in the glasshouse at 20°C. S. lineatus consumed more of the trifoliate component of the seedling. Sitona adults caused significant yield reduction at all levels of plant population. Total clover consumption increased with increasing size of sitona population, but consumption per adult weevil was reduced.     

Host selection behaviour of the banded pine weevil,Pissodes castaneus (Coleoptera: Curculionidae)

1. Pissodes castaneus represents an emerging pest species for Pinus spp. production in Latin America. This species attacks all the cultivated pine species in Patagonia Argentina causing wood damage and tree death. The objectives of this work were to describe the host preference behaviour of P. castaneus and the influence of wood damage by conspecifics on its host selection.
2. In two-choice bioassays, P. castaneus showed a feeding preference for Pinus contorta over P. ponderosa. However, percent weight gain when feeding on either species was similar.
3. In other bioassays, P. castaneus spent more time in areas with twigs on which other conspecifics had recently fed, although they were able to successfully feed on twigs without previous damage.
4. These results show that while P. castaneus can successfully colonize different pine species, P. contorta may be more susceptible to attack than P. ponderosa. Silvicultural management should be prioritized considering the weevil's preference for attacking damaged hosts.

     

Effects and implications of antibiotic treatment on Wolbachia-infected vine weevil (Coleoptera: Curculionidae)

1 The parthenogenetic weevil Otiorhynchus sulcatus was collected from five geographical locations in the U.S.A. All weevils from each location were infected by Wolbachia belonging to supergroup B. 2 We hypothesized that treatment with tetracycline, which has been used to clear Wolbachia infection, would influence the reproduction of Wolbachia‐infected parthenogenetic O. sulcatus females. Tetracycline treatment of preovipositional O. sulcatus females specifically inhibited egg hatching but had no effect relative to controls on any other physiological trait. 3 Treatment with gentamicin, which reportedly has no effect on Wolbachia infection but is indistinguishable from tetracycline in inhibiting protein synthesis of other bacterial genera, did not influence egg hatching. 4 These findings strongly suggest that the inhibition of egg development results from the antibiotic effect on Wolbachia rather than by direct toxic effects on O. sulcatus physiology. 5 We speculate that Wolbachia may be necessary for normal development of O. sulcatus eggs and discuss the implications of these findings for O. sulcatus ecology.     

Impact of azadirachtin on vine weevil (Coleoptera: Curculionidae) reproduction

Abstract 1 The dose–response of azadirachtin on vine weevil, Otiorhynchus sulcatus (Fabricius), reproduction is investigated by confining adults to feed on treated Taxus × media leaves, and by counting and evaluating development in the resulting eggs. 2 A dosage‐dependent reduction in oviposition is discovered for foliar surface residues of azadirachtin, with an EC₅₀ of 25–50 parts per million (p.p.m) and 99.2% inhibition of viable egg production with 100 p.p.m. 3 Switching weevils from treated to untreated foliage allows reproductive capability to be restored for weevils that cease egg laying after azadirachtin exposure of 50 p.p.m. Weevils that had already started laying eggs in untreated groups soon cease oviposition once switched to azadirachtin‐treated foliage. 4 A transovarial effect results in a decrease in the percentage of viable eggs as the azadirachtin concentration increases. 5 The amount of feeding on foliage does not appreciably decrease at these hormonally effective concentrations, and adult weevil mortality is only slightly greater in the azadirachtin‐treated groups. Therefore, the overall effect of azadirachtin on weevil populations in the field is difficult to assess, except by collecting weevils to determine whether they are able to lay viable eggs.     

Delimiting baridine weevil evolution (Coleoptera: Curculionidae: Baridinae)

Since the erection of the weevil subfamily Baridinae by Schönherr in 1836, no phylogenetic hypothesis using cladistic methods has been proposed for this extraordinarily diverse group. This study provides the first hypothesis for the evolution of Baridinae using phylogenetic methods, including 301 taxa and 113 morphological characters. Despite fairly well‐resolved results, indicating paraphyly of nearly all of the currently recognized intrasubfamilial divisions, no change to the current classification is made. Even though groupings are proposed based on the final results, it is believed that more rigorous analyses need to be made prior to a re‐evaluation and subsequent alteration of the current classification. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010.     

Characterization of olfactory receptor neurons for pheromone candidate and plant volatile compounds in the clover root weevil,Sitona lepidus

Antennal olfactory receptor neurons (ORNs) for pheromone and plant volatile compounds were identified and characterized in male and female clover root weevil, Sitona lepidus (Gyllenhal), using the single sensillum recording technique with five pheromone-related compounds, and 40 host and non-host plant volatile compounds. Overall, seven different types of olfactory sensilla containing specialized ORNs were identified in each sex of S. lepidus. Among them, three different types of sensilla in the males and two types in the females housed ORNs specialized for pheromone-related compounds. The ORNs in males were specialized for 4-methyl-3,5-heptanedione or one or more of four stereoisomers of 5-hydroxy-4-methyl-3-heptanone. In contrast, female sensilla did not contain ORNs sensitive to 4-methyl-3,5-heptanedione while they contained ORNs sensitive to and specialized for the stereoisomers of (4S,5S)-5-hydroxy-4-methyl-3-heptanone. In addition to the pheromone-related ORNs, four types of olfactory sensilla contained ORNs responsive to plant volatile compounds in male S. lepidus, and five types in females. Most of the ORNs identified in S. lepidus showed a high degree of specificity to specific volatile compounds although some of the active compounds showed overlapping response spectra in the ORNs across different types of sensilla. The most active plant volatile compounds were the four green leaf volatile compounds, (E)-2-hexenol, (Z)-2-hexenol, (Z)-3-hexenol and (E)-2-hexenal, and isomers of two monoterpenols, (±)-linalool and (±)-α-terpineol, all eliciting strong responses from relatively large numbers of ORNs in male and female S. lepidus. Our study indicates that S. lepidus has a set of highly sensitive and selective ORNs for pheromone and plant volatile compounds. Further work is needed to elucidate the behavioral implications of these findings.     

First record of Sitona discoideus Gyllenhal 1834 (Coleoptera: Curculionidae) on Norfolk Island

Abstract

The first records of Sitona discoideus and Trifolium repens on Norfolk Island are reported. The identities of both species were confirmed using morphological criteria and nucleotide sequences. Sequence data from the mitochondrial gene cytochrome oxidase subunit 1 of the Norfolk Island S. discoideus specimens were compared with 33 specimens from Australia, New Zealand and France. These data represent the first published sequences for S. discoideus, and suggest that Australia or New Zealand was the source of Norfolk Island's population. The implications of the introduction of S. discoideus to Norfolk Island are discussed.     

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.     

Temperature-dependent development and reproduction of the boll weevil (Coleoptera: Curculionidae)

Abstract Effects of temperature on development, survival, and fecundity of boll weevil, Anthonomus grandis grandis Boheman, were assessed at 10, 11, 12, 15,20,25,30,35,45, and 46 °C; 65% relative humidity; and a photoperiod of 13:11 (L: D) h. The mortality of boll weevil immature stages was 100% at 12°C and decreased to 36.4% as the temperature increased to 25°C. When the temperature increased from 30 °C to 45 °C, the mortality of weevils also increased from 50.1% to 100%. From 15°C to 35°C, the bollweevilpreimaginal development rate was linearly related to temperature. The average development time of total boll weevil immature lifestages decreased 3.6-fold and the preovipositional period decreased 3.3-fold when the temperature was increased from 15°C to 30°C. The lower threshold for development was estimated at 10.9, 6.6, 7.0, and 9.0 °C for eggs, larval, pupal, and total immature stages, respectively, with total thermal time requirement to complete immature stages of 281.8 DD (degree day) (15°C) and 247.8 DD (35 °C). At 1LC and 46°C, weevil females did not oviposit. Longevity of adult females decreased 4.6-fold with increasing temperatures from 15°C to 35°C. Fecundity increased with increasing temperatures up to 30°C and significantly decreased thereafter. These findings will be useful in creating a temperature-based degree-day model for predicting the occurrence of key life stages in the field. An accurate predictor of a pest's development can be very important in determining sampling protocols, timing insecticide applications, or implementing an integrated pest management control strategy targeting susceptible life stages.     

Speciation in the sub-Antarctic weevil genus Dusmoecetes Jeannel (Coleoptera: Curculionidae)

Relatively few instances of sympatric speciation have been reported in the literature, and both theoretical and empirical studies of this mode of speciation remain controversial. Recently, a model of sympatric speciation less restrictive than earlier ones has been proposed. This study presents a hypothetical speciation scenario, based on current observations, which seems to be consistent with the new model. Two morphologically similar, though ecologically separated, species are identified in the Dusmoecetes similis (C. O. Waterhouse) species complex on Marion Island (46° 54'S, 37° 45'E), based on a study of the morphology, biology and ecology of the group. Differences between the demands placed on angiosperm- and bryophyte-feeding members of the complex, and the differing demands of bryophyte and angiosperm-dominated communities, coupled with low vagility and a high degree of assortative mating, suggest that a sympatric model can be used to explain speciation in this genus, which probably occurred within the last 10,000 years. Differences between Dusmoecetes marioni Jeannel and D. Similis (Waterhouse) are discussed, and a lectotype designated for the latter species.     

Effects of kaolin-based particle film application on boll weevil (Coleoptera: Curculionidae) injury to cotton

This study examined a non-insecticidal tactic for suppressing boll weevil, Anthonomus grandis grandis Boheman, damage to cotton, Gossypium hirsutum L. In cage assays, kaolin, a reflective white mineral, applied to excised cotton squares or to the cotton foliage, initially resulted in lower levels of boll weevil injury to squares than nontreated squares. Boll weevil oviposition and feeding on kaolin-treated squares and squares on kaolin-treated cotton plants increased when nontreated squares and cotton plants were in short supply. A laboratory assay and field trials suggested that boll weevils distinguished between cotton plots based on color differences caused by kaolin and this appeared to influence levels of damage to squares. Random sampling in small plots indicated that oviposition damage to squares in plots treated with kaolin was reduced (P < 0.05) compared with nontreated controls, except when rain washed the kaolin off the foliage. Lint yield differences were not detected between the small plots, but the kaolin-treated small plots yielded as much as 2.36 times more cotton lint than a large but unreplicated adjacent nontreated control plot, and up to 1.39 times more than another large but unreplicated adjacent plot sprayed twice with preemptive applications of azinphosmethyl when cotton squares were first developing (pinhead stage). Potentially important avenues for future research on boll weevil injury suppression using kaolin are discussed.     

Size-dependent feeding and reproduction by boll weevil (Coleoptera: Curculionidae)

The considerable variation in adult size of the boll weevil, Anthonomus grandis grandis Boheman, has been well documented, but the influences of adult size on reproductive rate are not known. We examined the relationship between the size of boll weevils and their feeding and oviposition. Weevils weighed to the nearest milligram were grouped into five categories based on pupal weight: < or =5, 6-10, 11-15, 16-20, and >20 mg. Numbers of lifetime punctures produced in flower buds (squares) of cotton, Gossypium hirsutum L., by both sexes of adults tended to increase with pupal weight. Boll weevil females with pupal weights >10 mg produced progeny with significantly higher survival to adulthood and also produced a higher percentage of female progeny than those with pupal weights < or =10 mg. The population growth indices for females having pupal weights >10 mg averaged 1.8-fold higher than those of females weighing < or =10 mg. Survivorship of adults of both sexes also tended to increase with pupal weight. The percentage of females laying eggs on any given day averaged 2.1 times higher when their pupal weights were >10 mg than when their pupal weights were < or =10 mg. Although small size negatively affected female reproductive potential, even extremely small females produced some viable offspring. However, the penalties of small adult size, in terms of longevity and reproductive potential, suggest that cultural practices that result in the production of small adults may be used to impact weevil populations.     

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.     

Fine-tuning the composition of the cranberry weevil (Coleoptera: Curculionidae) aggregation pheromone

The cranberry weevil Anthonomus musculus Say is a key pest of highbush blueberries (Vaccinium corymbosum L.) and cranberries (Vaccinium macrocarpon Aiton) in the northeastern United States. Previous studies have reported A. musculus adult attraction to traps baited with the aggregation pheromone of the pepper weevil Anthonomus eugenii Cano, likely because these two weevils share similar pheromone blends that differ only in two components. The A. musculus aggregation pheromone contains (Z)-2-(3,3-dimethylcyclohexylidene) ethanol (Z grandlure II), (Z)-(3,3-dimethylcyclohexylidene) acetaldehyde (grandlure III), (E)-(3,3-dimethylcyclohexylidene) acetaldehyde (grandlure IV) and (E)-3,7-dimethyl-2,6-octadien-1-ol (geraniol); whereas A. eugenii produces a pheromone blend that includes (E)-2-(3,3-dimethylcyclohexylidene) ethanol (E grandlure II) and (E)-3,7-dimethyl-2,6-octadienoic acid (geranic acid) in addition to the four A. musculus pheromone components. Here, we hypothesized that differences in pheromone composition between these two species influence A. musculus adult attraction to its aggregation pheromone. To test this, we studied the response of A. musculus to its pheromone blend with and without E grandlure II and geranic acid, a commercial A. eugenii pheromone lure and a no-lure control in highbush blueberry and cranberry fields in New Jersey and Massachusetts, respectively. Regardless of crop type, A. musculus adults were more attracted to their four-component pheromone blend and the blend plus geranic acid than the commercial A. eugenii pheromone and the no-lure controls. The A. musculus pheromone blend plus E grandlure II and the A. eugenii pheromone blend also captured more A. musculus adults than the no-lure control but not compared to the commercial A. eugenii pheromone. Further analysis showed that A. musculus adults are significantly (~27%) less attracted to their pheromone blend if it contains E grandlure II, although the addition of geranic acid did not affect their response. These findings may help guide future efforts towards the development of behaviour-based tools to monitor and manage A. musculus.     

Effects of root nodules and taproots on survival and abundance of Sitona hispidulus (Coleoptera: Curculionidae) on Medicago sativa

ABSTRACT.

• 1 The effects of food resources on populations of larvae of Sitona hispidulus (F.), a root and nodule herbivore of Medicago sativa L., were investigated in 1983 and 1984.
• 2 Density-dependent mortality among first-instar larvae indicated that a lack of available root nodules, the primary resource for first instars, contributed to the 66.2±5.2% and 80.7±4.1% mortalities of first-instar larvae in 1983 and 1984, respectively. Initial densities of larvae entering the soil were 31.7±2.4 and 15.6±1.3 per soil sample (10.5 cm diam. ×15 cm deep) in 1983 and 1984, respectively (±SEM).
• 3 Survivorship and number of first-instar larvae per soil core sample were significantly related to number and biomass of nodules per soil sample. Percentage soil moisture was not consistently correlated with survivorship and number of larvae per soil sample.
• 4 Numbers of second- and third-instar larvae were not consistently correlated with either nodule or taproot biomass.
• 5 Numbers of fourth-instar larvae were associated with taproot biomass, suggesting that taproot surface area may also limit population levels of S.hispidulus. No correlations were found between taproot and nodule biomass on any sampling date indicating that high numbers of fourth-instar larvae associated with larger taproots were not merely due to a greater survival of first instars associated with larger taproots.
• 6 The study suggests that population levels of nodule-herbivores are controlled by the availability of root nodules. A sparse distribution of nodules results in high levels of mortality among nodule-herbivores of Medicago sativa.