Reduced Weevil Damage Research Articles

Biogenic secondary organic aerosol participates in plant interactions and herbivory defense.

Biogenic secondary organic aerosols (SOAs) can be formed from the oxidation of plant volatiles in the atmosphere. Herbivore-induced plant volatiles (HIPVs) can elicit plant defenses, but whether such ecological functions persist after they form SOAs was previously unknown. Here we show that Scots pine seedlings damaged by large pine weevils feeding on their roots release HIPVs that trigger defenses in neighboring conspecific plants. The biological activity persisted after HIPVs had been oxidized to form SOAs, which was indicated by receivers displaying enhanced photosynthesis, primed volatile defenses, and reduced weevil damage. The elemental composition and quantity of SOAs likely determines their biological functions. This work demonstrates that plant-derived SOAs can mediate interactions between plants, highlighting their ecological significance in ecosystems.

Evaluating combined effects of pesticide and crop nutrition (with N, P, K and Si) on weevil damage in East African Highland Bananas.

Banana weevil (Cosmopolites sordidus, Germar) is a major pest in East African Highland Banana. The influence of crop nutritional status on weevil damage is poorly understood. Nutrient availability affects the nutritional quality of plants for weevils and may affect weevil damage. Here, we evaluate the effect of insecticides alone and in combination with fertilisers (N, P, K and Si) on weevil damage using data from two experiments in central and southwest Uganda. In the first experiment, we varied chlorpyrifos and application rates of N, P and K. In the second experiment, we varied the application rates of K and Si. Treatment effects were analysed using generalised linear mixed models with a negative binomial distribution. In the first experiment, chlorpyrifos reduced and N increased weevil damage, while P and K had no significant effect. In the K or Si application rates reduced weevil damage compared with the control. We conclude that the combined application of chlorpyrifos with K and Si fertilisers can contribute to weevil damage control on sites with low nutrient availability and should form part of integrated weevil management in bananas. Future studies should assess how much reduction in insecticide use is possible in EAHB with judicious input rates.

Non‐pesticide alternatives for reducing feeding damage caused by the large pine weevil (Hylobius abietis L.)

AbstractThe large pine weevil (Hylobius abietis L.) is an important pest of young forest stands in Europe. Larvae develop under the bark of freshly cut pine and spruce stumps, but maturing weevils feed on the bark of coniferous seedlings. Such seedlings frequently die because of bark consumption near the root collar. We tested the effect of three treatments (the insecticide alpha cypermethrin, a wax coating and a glue coating) on the feeding damage caused by H. abietis on Douglas fir (Pseudotsuga menziesii) and Norway spruce (Picea abies) seedlings under semi‐natural conditions. In two experiments (one in 2016 and another in 2017) seedlings in cages were subjected to pine weevil feeding for 16 weeks under shaded outdoor conditions. The experiment in 2016 compared insecticide and wax treatments and an untreated control on Douglas fir and Norway spruce, and the experiment in 2017 compared insecticide, wax and glue treatments and an untreated control on Norway spruce. In both experiments, all treatments significantly reduced H. abietis feeding damage at week 8 at the end of both experiments (week 16); the effect of treatments was significant only on spruce seedlings. The damages on Douglas fir seedlings was less on treated seedlings than on untreated control seedlings but differences were not significant. Coating stems with glue and especially with wax was generally effective at reducing weevil damage and in most cases provided control that was not significantly different from that provided by insecticide treatment. Our results suggest that a wax coating has the potential to replace the protection of seedlings provided by insecticides.

Screening barrier plants to reduce crop attack by sweet potato weevil (Cylas formicarius).

Sweet potato weevil, Cylas formicarius (Fabricius) attacks stems and storage roots of sweet potato, Ipomoea batatas, and is a major pest of this globally significant crop. To minimize the immigration of weevils into sweet potato fields from nearby donor habitat, we assessed scope for a barrier plant approach. Here, we report a novel, two-stage, multiple choice olfactometer method to screen candidate barrier plant species and a field study of the effects of shortlisted barrier plants of weevil movement and plant damage. Initial work established that a combination of sweet potato foliage and storage root was significantly more attractive to adult C. formicarius than either tissue alone in the distal chamber of choice arms. Among 15 candidate barrier plant species in intermediate chambers in arms, spring onion, oregano, chilli, basil, sweetcorn, fennel, lime mint and lemongrass significantly reduced passage of C. formicarius. Of these, sweetcorn and lime mint significantly reduced the numbers of oviposition holes in sweet potato storage roots. A field study showed that basil and chives were effective barrier plants for reducing weevil damage to sweet potato storage roots. Our method has utility for screening additional candidate plants, and suggests that weevil dispersal and subsequent oviposition are affected by passage through some plants, suggesting scope for barrier plants to contribute to the management of this major pest. © 2019 Society of Chemical Industry.

Phenotyping tree resistance to a bark‐chewing insect, the pine weevil Hylobius abietis

AbstractBreeding for resistance to forest pests and pathogens is emerging as a promising tool for minimising the impact of the increasing biotic threats that our forests are experiencing as a consequence of global change. Efficient phenotyping protocols of resistance are urgently needed. Here we present the results of two experiments aimed to determine whether the variation in resistance to the pine weevil Hylobius abietis, a harmful pest of European conifers, can be inferred by nondestructive bioassays using excised plant material collected in forest genetic trials. Weevil damage and amount of nonvolatile resin induced by weevil feeding were assessed in young trees and in branches of adult trees using several phenotyping procedures (bioassays using either living trees, excised plant material and cut stem twigs) on four pine species (Pinus pinaster, P. radiata, P. sylvestris and P. pinea). Half of the plants were previously induced with methyl jasmonate (MJ), a treatment that is known to affect resistance to the pine weevil. In Experiment 1, living and excised plants showed parallel results: MJ treatment significantly reduced weevil damage, and saplings responded to weevil damage locally increasing the nonvolatile resin (NVR) in the stems proportionally to the damage suffered. This response was, however, slightly lower in excised than in living saplings. On the contrary, patterns of weevil feeding on stem twigs completely departed from those observed in living and excised seedlings. Moreover, cut stem twigs were unable to respond to weevil feeding increasing NVR according to the weevil damage. In Experiment 2, assessment of weevil damage on excised branches explained around 50% of variation in damage on living branches. This relationship became much more pronounced (R2 = 0.81) when explored at the mean treatment level; branch manipulation did not alter the patterns of variation in resistance across pine species or MJ treatments. Irrespective of the assessment procedure, MJ consistently decreased weevil damage in all pine species, with larger reduction in weevil damage in stone and maritime pine than in radiata and Scots pine. Radiata pine was the most resistant while Scots pine was the most susceptible to the pine weevil. Overall, results suggest that using excised plant material is an operative alternative for phenotyping weevil resistance whenever care is taken to maintain the functionality of the excised plant material. This will allow taking advantage of multiple available conifer genetic trials to deepen the ecological genetics of resistance to the pine weevil and to screen for resistance without compromising the long‐term utility of those genetic trials.

Effects of methyl jasmonate on the concentration of volatile terpenes in tissues of Maritime pine and Monterey pine and its relation to pine weevil feeding

Understanding pine weevil [Hylobius abietis (L.)] feeding preferences and their relations to chemical defenses of pines may lead to improved protection of conifer seedlings across Europe and Asia. Previous studies showed reduced weevil damage in methyl jasmonate (MeJA) treated seedlings and that weevil preference for Monterey pine (Pinus radiata Ait.) or Maritime pine (Pinus pinaster D. Don) depended on feeding conditions. The present study explored whether volatile terpenes in plant tissues of control and MeJA-treated seedlings of these two pine species could explain differences in weevil feeding and seedling growth. Volatile terpenes of hexane extracts of needles and phloem were separated and identified by gas chromatography–mass spectrometry (GC–MS). The results confirmed that MeJA application reduced pine weevil feeding in both pine species, but the increase in resistance was not explained by any general change in the concentration of mono- and sesquiterpenes after MeJA application. MeJA effects on volatile terpenes differed between the two pine species. Responses to MeJA application were more intense in Monterey pine, for which total mono- and sesquiterpenes were induced and growth rates affected, even at the lowest concentration of MeJA (5 mM). In Maritime pine, seedling growth was affected only at the highest MeJA concentration (25 mM), and no effect was observed on total volatile terpenes. Contrasting effects of MeJA on key monoterpenes were also observed. In needles, the content of (−)-β-pinene, a monoterpene with deterrent properties against the pine weevil, increased in MeJA-treated seedlings of Monterey pine, but not in Maritime pine. In the phloem of Maritime pine, the MeJA treatment reduced the concentration of the pine weevil attractant (+)-α-pinene, whereas it was increased in Monterey pine. Altogether, results indicated that weevil preferences between the two species could be altered if resistance of seedlings were previously induced with MeJA. The differential inducibility of key volatile terpenes between the two pine species may be part of the explanation as to why pine weevil preferences to the two pine species differ between field and lab conditions.

Genetic variation in resistance of Norway spruce seedlings to damage by the pine weevil Hylobius abietis

Regeneration of northern conifer forests is commonly performed by reforestation with genetically improved materials obtained from long-term breeding programs focused on productivity and timber quality. Sanitary threats can, however, compromise the realization of the expected genetic gain. Including pest resistance traits in the breeding programs may contribute to a sustainable protection. Here we quantified the variation in different components of resistance of Norway spruce to its main pest, the pine weevil Hylobius abietis. We followed insect damage in two large progeny trials (52 open-pollinated families with 100–200 individuals per family and trial) naturally infested by the pine weevil. Pine weevils damaged between 17 and 48% of the planted seedlings depending on the trial and year, and mortality due to weevil damage was up to 11.4%. The results indicate significant genetic variation in resistance to the pine weevil, and importantly, the variation was highly consistent across trials irrespective of contrasting incidence levels. Individual heritability estimates for the different components of seedling resistance were consistently low, but family heritabilities were moderate (0.53 to 0.81). While forward selections and breeding for higher resistance seem not feasible, backwards selections of the best parent trees emerge as a putative alternative to reduce weevil damage. A positive genetic correlation between early growth potential and probability of being attacked by the weevil was also observed, but the relationship was weak and appeared only in one of the trials. Overall, results presented here open the door to a new attractive way for reducing damage caused by this harmful pest.

Plant genotypes affect aboveground and belowground herbivore interactions by changing chemical defense.

Spatially separated aboveground (AG) and belowground (BG) herbivores are closely linked through shared host plants, and both patterns of AG-BG interactions and plant responses may vary among plant genotypes. We subjected invasive (USA) and native (China) genotypes of tallow tree (Triadica sebifera) to herbivory by the AG specialist leaf-rolling weevil Heterapoderopsis bicallosicollis and/or the root-feeding larvae of flea beetle Bikasha collaris. We measured leaf damage and leaves rolled by weevils, quantified beetle survival, and analyzed flavonoid and tannin concentrations in leaves and roots. AG and BG herbivores formed negative feedbacks on both native and invasive genotypes. Leaf damage by weevils and the number of beetle larvae emerging as adults were higher on invasive genotypes. Beetles reduced weevil damage and weevils reduced beetle larval emergence more strongly for invasive genotypes. Invasive genotypes had lower leaf and root tannins than native genotypes. BG beetles decreased leaf tannins of native genotypes but increased root tannins of invasive genotypes. AG herbivory increased root flavonoids of invasive genotypes while BG herbivory decreased leaf flavonoids. Invasive genotypes had lower AG and BG herbivore resistance, and negative AG-BG herbivore feedbacks were much stronger for invasive genotypes. Lower tannin concentrations explained overall better AG and BG herbivore performances on invasive genotypes. However, changes in tannins and flavonoids affected AG and BG herbivores differently. These results suggest that divergent selection on chemical production in invasive plants may be critical in regulating herbivore performances and novel AG and BG herbivore communities in new environments.

Flaming Dormant Alfalfa for Pest Control

Alfalfa (Medicago sativa Leyss) is an important forage crop whose production is hampered by pests, including the alfalfa weevil (Hypera postica Gyllenhal) which is a major problem in many areas. Flaming during dormancy could be an alternative control measure. Late fall and early spring flaming at three intensities were compared with pesticide and no treatment for their effects on alfalfa weevil damage and weed density. In four site-years, flaming at high intensity generally reduced weevil damage to alfalfa. When winter annual broadleaf weeds were prevalent, flaming decreased their density. When fall and spring flaming effects were different, spring flaming gave better results.

ECOLOGY-BASED INTEGRATED MANAGEMENT OF THE SWEETPOTATO WEEVIL IN INDIA

The production of sweetpotato is often hampered by the ubiquitous sweetpotato weevil. Feeding by the weevil renders the roots unfit for consumption due to the bitter and toxic sesquiterpenes produced. The concealed feeding habits of grubs and nocturnal habits of adults make the management of the pest a challenge. IPM strategies reported here are based on a number of experiments and observations over a period of 10 years, and involve behaviour manipulation (mass trapping of adult weevils using a sex pheromone) and agronomic practices based on the crop phenology and weevil life-table. The IPM package developed was a combination of weevil-free planting material, mulching with Calophyllum inophyllum or Bassia latifolia cake at 2 t ha -1 or mulching the plant base with leaves of Clerodendron infortunatum or Chromolaena odorata at 3 t ha -1 , reridging, mass trapping of males through sex pheromone traps, preservation of biocontrol agents, disposal of harvest residues and early harvesting. This package was found to reduce weevil damage in the field and increase the number of marketable roots. It was successfully tested in farmers' fields over 14 states of India.

Evaluation of foliar and seed treatments for control of the cabbage seedpod weevil (Coleoptera: Curculionidae) in canola

AbstractCaged assays and field tests were used to evaluate the effectiveness of organophosphorus, pyrethroid, neonicotinoid, and biologically derived insecticides for reducing populations of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), a new pest of canola in Canada. Complete mortality of caged weevils occurred 48 h after treatment with disulfoton, deltamethrin, carbofuran, oxydemeton-methyl, and chlorpyrifos. Under field conditions, using plots or large strips in commercial fields from 1998 to 2001, only deltamethrin and cyhalothrin-lambda (both pyrethroids) consistently reduced weevil densities, even at high population levels. Chlorpyrifos also significantly reduced weevil numbers and damage in some years, but results were variable and efficacy was too low to manage weevils under outbreak densities. Other insecticides such as spinosad provided moderate weevil control and may have a role in weevil management depending on their effect on beneficial insects relative to more efficacious insecticides. Treatment of canola seed with imidacloprid, lindane, or acetamiprid did not reduce weevil damage. Further research is needed to establish economic thresholds for C. obstrictus in canola, to assess the effect of insecticides on nontarget natural enemies of canola insect pests, and to assess the potential for integration of chemical agents with biological and cultural control strategies.

Evaluation of the impact of sweetpotato weevil (Cylas formicarius) and of the effectiveness of Cylas sex pheromone traps at the farm level in Indonesia

We evaluated the impact of sweetpotato weevil ( Cylas formicarius (Fabricius); Coleoptera: Apionidae) and of other direct pests and diseases (rats, Ceratocystis fimbriata, white grubs, rootrots and root cracks), and the effectiveness of C. formicarius sex pheromone traps at the farm level in four villages in East and Central Java, Indonesia during 1994 - 1996. Marketable yields of sweetpotato and damage from weevils and from other pests and diseases were higher during the dry season, when damage from weevils reached 8.2% and the impact of other pests and diseases was 16.3%, reducing marketable yield from 3.32 to 2.50 kg/m2. During the wet season damage from sweetpotato weevil and from other pests and diseases dropped to 2.1 and 12.7% respectively. Varietal differences in damage from weevil and from other pests and diseases were not significant. In field trials with sex pheromone, lure loadings of 10, 50 and 100 mug placed at trap densities of 9, 25 and 100 traps/ha the average yield was 2.41 kg/m2 with sweetpotato weevil and other direct pests and diseases accounting for losses of 2.7% and 4.7% respectively. However, there were significant location-specific differences in weekly trap catch averages and in seasonal trap catch patterns. Trap catches ranged from averages of 475 and 584 weevils/week in the villages of Bendunganjati and Turi to 254 and 46 weevils/week in Ngargoyoso and Kradenan. The highest trap catches occurred at the highest sex pheromone loadings in all four locations. The effect of trap density on average weekly trap catch depended on location, with no significant effect of trap density on trap catch when the data from all locations were pooled. There was no statistically significant impact of sex pheromone traps on losses from sweetpotato weevil, although fields with blank lures had consistently higher levels of sweetpotato weevil damage. The highest trap catches occurred in Turi, which also had the highest levels of weevil damage. The use of sex pheromone traps led to damage reduction, even when weevil pressure and damage levels were low, as in the village of Kradenan. This suggests that there is potential for traps to play a role in reducing weevil damage in situations of higher weevil pressure.

Control of White Pine Weevil in Young Jack Pine Plantations with Permethrin and Methoxychlor

Abstract The efficacy of mistblower applications of permethrin at 70 g and 140 g active ingredient (ai)/ha and methoxychlor at 1.1 kg ai/ha was evaluated for the control of white pine weevil in young jack pine plantations. The results from 2 yr of testing indicate that 1-3% of the leaders were weevil-damaged after insecticide treatment compared to 9-13% in untreated plantations. Generally, all three insecticide treatments were similarly effective in reducing weevil damage. Additional field trials with permethrin at 70 g ai/ha showed that effective applications can be made as late as 2 wk after the first weevils have emerged in the spring from the soil. Mistblower applications of permethrin and methoxychlor can be an effective method to control the weevil in high value jack pine plantations such as seed orchards and genetic test sites where silvicultural and cultural control techniques are impractical. North. J. Appl. For. 12(1):19-22.

Field Efficacy and Persistence of Entomopathogenic Nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) for Control of Sweetpotato Weevil (Coleoptera: Apionidae) in Southern Florida

The entomopathogenic nematodes Steinernema carpocapsae (Weiser) (All, S17, and S20 strains), S. feltiae (Filipjev) (= S. bibionis) (N27 strain), Heterorhabditis bacteriophora (Poinar) (HP88 strain), and Heterorhabditis sp. (Bacardis strain) were evaluated as biological control agents of the sweetpotato weevil, Cylas formicarius (F.), during two consecutive growing seasons in southern Florida. Two strains, S17 and S20, were genetically selected over 17 and 20 generations, respectively, for enhanced finding of the host scarab Popillia japonica Newman. Steinernematid nematodes were applied as aqueous suspensions. The heterorhabditid nematodes, tested only in the second year, were applied using cadavers of greater wax moth, Galleria mellonella (L.), infected with these nematodes. Abundance and damage of weevils differed among nematode treatments. In the first experiment, S. carpocapsae All and S17 were most efficacious at reducing weevil damage and produced the highest percentages of marketable roots. In the second experiment, the heterorhabditid nematode, HP88, was most efficacious at reducing weevil damage to storage roots. All of the steinernematids, except S20 applied at a high rate (7.9 billion infective juveniles per ha), produced comparable percentages of marketable roots but were less efficacious than HP88. In the first experiment, S. carpocapsae All and S17 persisted poorly, whereas S. feltiae N27 persisted for >160 d after application. In the second experiment, most nematodes were recovered at moderate levels for >120 d after application; however, only Heterorhabditis sp. Bacardis was consistently recovered at high levels for >230 d after application.

Potential of Entomopathogenic Nematodes as Biological Control Agents of Sweetpotato Weevil (Coleoptera: Curculionidae)

The entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (= H. heliothidis Khan, Brooks, & Hirschmann) (HP88 strain) and Steinernema (=Neoaplectana ) carpocapsae Weiser (All and G-13 strains) were evaluated as biological control agents of the sweet potato weevil, Cylas formicarius elegantulus (Summers). In Petri dish bioassays, all three strains were pathogenic to larvae and pupae of C. f. elegantulus . The LD50 values of C. f. elegantulus larvae were 2.6, 2.9, and 3.4 infective juveniles per insect for ‘All,’ ‘G-13,’ and ‘HP88,’ respectively. The LD50 values of pupae were 4.9, 5.9, and 4.8 infective juveniles per insect for these three nematodes, respectively. Virulence did not differ among strains or between life stages within each strain. Under simulated field conditions, ‘G-13’ was most efficacious at killing weevil larvae within infested sweet potato ( Ipomoea batatas (L.) Lam.) roots followed in decreasing order by ‘HP88’ and ‘All’ nematodes. Efficacy in killing pupae within roots did not differ among the three nematodes or between life stages for each nematode. Field applications of ‘HP88’ and ‘All’ nematodes were more effective than chemical insecticides at reducing weevil densities on plants. ‘HP88’ nematodes were more effective than ‘All’ nematodes and chemical insecticides at reducing weevil damage to fleshy roots.

Influence of cultural pest management techniques on the infestation of sweetpotato weevil

In a series of field experiments conducted since 1977, various cultural pest management techniques have been tested to reduce damage by the sweetpotato weevil, Cylas formicarius formicarius F. Planting rice after harvest of the weevil-infested crop does not reduce weevil damage in the ensuing sweetpotato crop if the source of weevil is present in the vicinity. Rice rotation initiated away from the weevil source, coupled with removal of the common wild-host Ipomoea sp., can reduce weevil infestation and maximize the effectiveness of carbofuran transplant dip treatment. In order to reduce the weevil source from the weevil-infested sweetpotato of the previous season, a 2-week flooding of the field soon after harvest practically eliminated the number of volunteer sweetpotato plants and the weevil. Covering the planted area with rice straw or plastic mulch reduced weevil infestation.