Mortality Of Adult Weevils Research Articles

TOXICITY OF SOME BOTANICAL POWDERS ON MAIZE WEEVIL Sitophilus Zeamais MOTSCHULSKY 1855 (COLEOPTERA: CURCULIONIDAE)

Maize production system is challenged by a lot of biotic and abiotic stressors. Among the biotic stressors, the maize weevil is infamous for causing severe damage to stored maize, reducing both qualitative and quantitative qualities. Incessant use of synthetic insecticide to manage maize weevil has led to a public outcry and a need for more eco-compatible options. Botanicals provide a cheap, safe and easy-to-make, and eco-friendly option for maize weevil management. This study was designed to assess the toxicity of four medicinal plant powders on some parameters of maize weevil. The study was conducted in June-July, 2020 in the Food Science laboratory of Catholic University of Cameroon, Bamenda. Plant powders of Carica papaya seeds, Cupressus macrocarpa leaves, Piper nigrum seeds and a control (no-input) were assessed. All the parameters assessed were significantly influenced by botanical powders (P < 0.05). The highest F1 emergence suppression was observed from piper treatments, followed by cypress and pawpaw treatments. The highest and lowest maize weight loss after storage were 21.0g and 13.25g from control and piper treatments respectively. The highest germination percentage was 95.0%, followed by 80.0%, 75.0% and 52.5% from piper (bush pepper or black pepper, cypress, pawpaw and control treatment, respectively. High repellency potential was observed from botanicals and that of piper can be described as a ‘very good repellant’ and ‘good repellant’ for the other botanicals. The highest adult weevil mortality was 80.05, recorded from piper. The current study demonstrate that botanical powders can play a significant role in maize weevil management. Piper seed powder is highly recommended for management of maize weevil. In addition, it is recommended that botanical powders be incorporated into integrated pest management strategies in order to guarantee safe, healthy and quality maize in storage. Such activities are in line with the objective of sustainable development goals (SDG).

Effect of X-ray irradiation on the F1 generation of Sitophilus zeamais Motschulsky and the germination rate of maize grain

BackgroundThe use of X-ray irradiation in the control of the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) infesting stored maize was tested at 60, 70 and 80 KeV as part of the international concerted efforts to save maize production and enhance food security. Investigations were done in the laboratory at mean temperature and relative humidity of 29.2 °C and 75.7%, respectively using three varieties of maize. The possibility that X-ray irradiation can affect the viability of maize grains when planted after weevil control process was also evaluated in the laboratory. Standard methods were used to achieve the specific objectives, and X-ray machine snap constituted the exposure time for each dose.ResultsThe results revealed 10% mortality of adult weevils after 24 h and 40% mortality after a period of 7 days. The result indicates moderate effect on mortality. Progressive increase in mortality was recorded as dose increased from 60 to 80 KeV. X-ray irradiation at the doses tested did not significantly (P > 0.05) restrict S. zeamais emergence from maize grains and did not also significantly protect grains against damage and flour production. There was no difference in the pattern of daily emergence of new progenies and pattern of accumulated emergence. The relationship between X-ray irradiation doses and weight of emerging progenies require more specific analysis. Absence of significant difference between the viability of irradiated grains and un-irradiated grains strongly suggests that X-ray irradiation did not adversely affect seed viability, and this gives irradiation technique an opportunity of higher acceptability in agriculture.ConclusionsWe recommend > 80 KeV of X-ray irradiation or its incorporation into integrated pest management system in order to achieve effective post-harvest control of the pest.

Rolliniastatin-1, a bis-tetrahydrofuran acetogenin: The major compound of Annona mucosa Jacq. (Annonaceae) has potent grain-protective properties

The widespread use of synthetic insecticides results in insecticide-resistant populations of maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), a primary pest species of stored corn worldwide. Thus, new active ingredients with different modes of action are needed for integrated pest management (IPM) of stored grains. Thus, toxicological bioassays (using S. zeamais as bioindicator) associated to chromatographic techniques were performed to isolate insecticidal compounds from the grain-protective ethanolic extract of Annona mucosa Jacq. (Annonaceae) seeds. The acetogenin bis-tetrahydrofuran rolliniastatin-1 was identified as major bioactive constituent from A. mucosa seeds based on bioassay-guided fractionation, along with rolliniastatin-2, deethylrollinastatin-1, jimenezin and fractions containing triglycerides. This compound produced 51.1% of mortality of adult weevils when applied at 57.66 mg kg−1, drastically reducing F1 progeny and their damage to corn grains. Although the acute toxicity level was lower than that with the formulation based on diatomaceous earth at a concentration 17.3 times higher (Insecto®, at recommended rate) used as a positive control, rolliniastatin-1 protected grain statistically similar to that of the positive control. Furthermore, bioassays indicate that compounds of different chemical natures have a synergistic effect on the overall biological activity of seed derivatives of A. mucosa. Efficacy and technical viability of the process to obtain rolliniastatin-1 from the seeds of A. mucosa should allow the production of a botanical insecticide to control populations of S. zeamais at corn warehouses.

Effects of salinity and nutrients on water hyacinth and its biological control agent, Neochetina bruchi

Water hyacinth, Eichhornia crassipes (Mart.) Solms (Commelinales: Pontederiaceae), is an important aquatic weed worldwide. Previous studies demonstrate that releases of Neochetina bruchi Hustache (Coleoptera: Curculionidae) provide biological control in many locations, but not all. Notably, N. bruchi were unsuccessful at regulating water hyacinth in tidal brackish waters. Abiotic factors, including salinity and nutrients, affect water hyacinth growth, but little is known about the impact of salinity on weevil survival. We hypothesized that N. bruchi has a relatively low salinity tolerance. In a mesocosm experiment, we assessed weed growth in response to a range of salinity and nutrient concentrations. In a laboratory, we assessed adult N. bruchi mortality in response to various salinity concentrations. Results indicate that increasing nutrient concentration increases weed growth. When both nutrient and salinity levels were varied, nutrients increased leaf count, but not biomass, while salinity reduced growth and increased mortality. Increasing salinity concentrations increased adult weevil mortality; required concentrations were higher than that for weeds. Thus, these results did not provide support for the suggested hypothesis. Potential effects of salinity via other exposures to weevils need to be investigated. Elucidating abiotic factors important for weed growth and weevil survival may increase effectiveness of water hyacinth management practices.

Assessing New Tools for Management of the Pepper Weevil (Coleoptera: Curculionidae) in Greenhouse and Field Pepper Crops.

The pepper weevil, Anthonomus eugenii Cano, is an economically important pest of field and greenhouse pepper crops in North America. In this study, a series of insecticides covering a broad-spectrum of insecticidal modes of action were assessed for their potential in managing the pepper weevil under laboratory and greenhouse conditions. To accomplish this, laboratory mini-spray tower and greenhouse cage trials were conducted that evaluated the efficacy of 16 conventional, reduced-risk, and microbial insecticides. In laboratory trials, adult weevils were sprayed with insecticides, placed on treated leaves within a cup cage, and were monitored for their survival over 10 d. Of the 16 insecticides tested, 8 provided greater than 60% weevil control, a threshold considered necessary for including products in further greenhouse testing. In greenhouse trials, adult weevil mortality, bud and foliar damage, bud and fruit abortion, and subsequent weevil offspring emergence were measured following each of three weekly insecticide applications. The most efficacious insecticides included kaolin clay and mineral oil, which performed as well as the thiamethoxam-positive control, and incurred 70 and 55% of adult weevil mortality, respectively. Additionally, kaolin clay and mineral oil reduced offspring weevil emergence by 59 and 54%, respectively, compared with untreated controls. Despite the clear challenge that controlling this pest represents, this study has identified useful new tools for the integrated management of the pepper weevil, which may accelerate the rate at which these become available for use in greenhouse and field pepper production.

Winter and spring conditions determine the production of the salvinia weevil mass rearing programme

ABSTRACTInvasion from giant salvinia (Salvinia molesta Mitchell, Salviniaceae) blocks sunlight entering waterbodies, reducing submerged aquatic macrophytes, thus lowering dissolved oxygen and stressing aquatic organisms. Due to its rapid growth and ease of dispersal through fragmentation, giant salvinia can quickly become problematic and difficult to eradicate. Since invasion of giant salvinia is persistent, land managers need a cost-effective method of control. Biological control by the salvinia weevil (Cyrtobagous salviniae Calder and Sands, Coleoptera: Curculionidae) has proven successful in controlling giant salvinia, and at a fraction of the cost of chemical and mechanical control. To maintain a source of salvinia weevils for field releases, mass rearing in outdoor ponds by natural resource managers is common practice in tropical regions. Using number of freezing hours and degree-day calculator, we examined how winter and spring conditions impacted the production of weevils in mass rearing ponds across southern Louisiana, USA. We found that winter temperature determined adult weevil mortality while spring temperature dictated reproduction, larval appearance, and timing of pond harvest. During winters with <55 h of freezing temperatures, ponds maintained densities of at least 13 adult salvinia weevils kg−1. Winter with >200 hours of freezing temperature reduced adult density in the ponds nearly extirpating the population. Larvae were found on samples on average at 89 degree-days which began accumulating in January 1st. This study suggested that winter and spring conditions are critical for mass rearing operations and population growth of C. salviniae.

Susceptibility of selected maize seed genotypes to Sitophilus zeamais (Coleoptera: Curculionidae)

Studies were carried out under laboratory conditions of 25 ± 2 °C and 70 ± 5% RH in an incubator to determine the relative susceptibility of eighteen maize genotypes to attack by the maize weevil, Sitophilus zeamais Motschulsky. The experiment was laid out in a Completely Randomized Design (CRD) with three replications. Adult mortality, number of F1 progeny, weevil development time, susceptibility index, percentage seed damage, percentage weight loss, and weight of powder produced were determined after storage period of three months. The susceptibility index was determined using Dobie’s formula and the genotypes were classified into different susceptibility groups. The genotypes exhibited varying degrees of susceptibility to S. zeamais attack. Only Aseda was regarded as resistant and TZE-Y POP STR as moderately resistant to S. zeamais. Kpari-Faako, Tintim, WACCI-M-1215, WACCI-M-1594 and Wang-Dataa were regarded as moderately susceptible to S. zeamais. However, Abontem, Bihilifa, Ewul-Boyu, Sanzal-Sima, TZE-I 17, WACCI-M-1205, WACCI-M-1508 and WACCI-M-1510 were regarded as susceptible genotypes. Furthermore, Aburohemaa, Obaatanpa and Omankwa were regarded as highly susceptible to S. zeamais. Number of F1 progeny, seed damage, seed weight loss, weight of dust produced and seed moisture content had positive relationship with varietal susceptibility while adult weevil mortality, median development period and seed germination after infestation had an inverse relationship with susceptibility in maize. The use of insect resistant genotypes would offer a sustainable way of minimizing postharvest losses of seeds in storage especially for smallholder farmers who keep harvested grains for future use as food and seed.

Investigating the potential of an autodissemination system for managing populations of vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic fungi.

Vine weevil, also known as black vine weevil, (Otiorhynchus sulcatus) is an economically important pest affecting soft fruit and nursery stock in temperate regions. We used laboratory and polytunnel experiments to investigate a novel control system based on autodissemination of spores of an entomopathogenic fungus to populations of adult vine weevils. The fungus was applied as a conidial powder, used on its own or formulated with talc, to a simple plastic refuge for vine weevils. The potential for adult weevils to disseminate the fungus was investigated first in polytunnel experiments using fluorescent powders applied to the refuge in lieu of fungal conidia. In this system, 88% of adult weevils came in contact with the powder within 48 h. When the powder was applied to five adult weevils that were then placed within a population of 35 potential recipients, it was transmitted on average to 75% of the recipient population within 7 days. Three isolates of entomopathogenic fungi (Beauveria bassiana isolate codes 433.99 and 1749.11 and Metarhizium brunneum isolate code 275.86), selected from a laboratory virulence screen. These three isolates were then investigated for efficacy when applied as conidial powders in artificial refuges placed among populations of adult weevils held in experimental boxes in the laboratory at 20 °C. Under this regime, the fungal isolates caused 70-90% mortality of adult weevils over 28 days. A final polytunnel experiment tested the efficacy of conidial powders of M. brunneum 275.86 placed in artificial refuges to increase vine weevil mortality. Overall weevil mortality was relatively low (26-41%) but was significantly higher in cages in which the conidial powders were placed in refuge traps than in cages with control traps. The lower weevil mortality recorded in the polytunnel experiment compared to the laboratory test was most likely a consequence of the greater amounts of inoculum required to kill adult weevils when conditions fluctuate between favourable and unfavourable temperatures e.g. below 15 °C. The potential of an autodissemination system for entomopathogenic fungi as a means of controlling vine weevil as part of an integrated pest management programme is discussed.

Efficacy of Some Plant Extracts as Storage Protectants against Callosobruchus maculatus

A significant quantity of crops is lost as a result of application of non-selective crop protection agents. The agrochemical industry is faced with increasing demand for the development of new crop protection agents that are safe for the environment and consumers. This research aimed at contributing to the collation and organization of baseline data on natural insect repelling and insecticidal agents. It also aimed at discovering crop protection agents that would preferentially get rid of pests. The need to develop pest control measures as alternative to chemicals is a priority for Scientists worldwide. Therefore, it is critical to find a cost effective and non-toxic method to prevent pest attack on field or stored crops. In this study, Cymbopogon citratus (lemon grass), Citrus sinensis (orange peel) and Azadirachta indica (neem) were used to investigate and evaluate the potency of the fixed and essential oils of these plants as pest control agent for the main storage insect pest of cowpea- Callosobruchus maculatus. All extracts were toxic to adult C. maculatus and prevented egg hatching. However, Citrus sinensis showed the highest weevil mortality on the first day of exposure, followed by Azadirachta indica and the least toxic was Cymbopogon citratus in the fixed oil category of extracts while in the essential oil category, Cymbopogon citratus showed 100% adult weevil mortality within one hour of exposure and Citrus sinensis was able to achieve 100% weevil mortality at the third hour of exposure. The Gas Chromatography/Mass Spectrometry (GC/MS) analysis of the essential oils of Cymbopogon citratus and Citrus sinensis was used to identify possible components of the oils comparing with existing data. This led to the development of technique adoptable for small holder farmers and cowpea traders.

Virulence of entomopathogenic nematodes and their symbiotic bacteria against the hazelnut weevil Curculio nucum

AbstractThe virulence of different entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae, isolates from Catalonia (NE Iberian Peninsula), and their symbiotic bacteria was assessed with regard to the larvae and adults of the hazelnut weevil, Curculio nucum L. (Coleoptera: Curculionidae). The nematode strains screened included one Steinernema affine, five Steinernema feltiae, one Steinernema carpocapsae, one Steinernema sp. (a new species not yet described) and one Heterorhabditis bacteriophora. The pathogenicity of all the strains of nematodes was tested on larvae and only four of them on adults of the hazelnut weevil. Larval mortality ranged from 10% with S. affine to 79% with Steinernema sp. Adult mortality was higher in S. carpocapsae, achieving 100% adult weevil mortality. The pathogenicity of the symbiotic bacteria Xenorhabdus bovienii, X. kozodoii, X. nematophila and Photorhabdus luminescens was studied in larvae and adults of C. nucum. In the larvae, X. kozodoii showed a LT50 of 22.7 h, and in the adults, it was 20.5 h. All nematodes species except S. affine tested against larvae showed great potential to control the insect, whereas S. carpocapsae was the most effective for controlling adults.

Insecticidal Effect of Fruit Extracts from Xylopia aethiopica and Dennettia tripetala (Annonaceae) against Sitophilus oryzae (Coleoptera: Curculionidae)

The insecticidal and repellent activities of fruit extracts of Xylopia aethiopica (Dunal) A. Rich. and Dennettia tripetala (Baker f.) G.E. Schatz belonging to the family Annonaceae was studied against Sitophilus oryzae (L.), an economic, primary post-harvest pest of rice, and other cereal products. Infested rice grains (100 g) treated with 1, 2, 3, 4, and 5% (w/w) powders of both plants were evaluated for toxicity against S. oryzae every 24 h for 3 d, and during F1 progeny emergence. The essential oils of both plants were also applied at 0.5, 1, 1.5 and 2 mg cm-2 filter paper in Petri dishes for toxicity bioassays at 24 h exposure. Repellence bioassay with 10 μL solution of essential oils on filter paper was performed in a Y-Tube airflow olfactometer. Results indicate that powders of both plants significantly (P < 0.001) caused adult weevil mortality and a reduction in F1 progeny emergence than the control. Essential oils were also significantly (P < 0.001) adulticidal to S. oryzae after 24 h with the highest dose (2 mg cm-2) producing 100% mortality respectively. Similarly, both male and female weevils significantly avoided the test arm compared to the control arm in the Y-Tube olfactometer repellence tests. These results suggest that X. aethiopica and D. tripetala natural extracts have potential for use as part of integrated pest management of stored product protection against S. oryzae.

Hermetic on-farm storage for maize weevil control in East Africa

Maize (Zea mays L.) consumption makes up over half of daily caloric intake of persons in East Africa and adequate supply is necessary for food security for subsistence farmers, as well as for domestic stability. Hermetic post-harvest maize storage is an attractive non-chemical control strategy for maize weevil,Sitophilus zeamais (Motsch.), which is the principal cause of insect damage to stored maize grain. Laboratory experiments were conducted on instrumented hermetic and non-hermetic containers to measure effects of temperature (10 vs. 27°C) and maize moistures (6.3 to 16%) on maize weevil biology and mortality rate, and to quantify weevil oxygen consumption. Ten days weevil mortality was significantly higher in hermetic vs. non-hermetic storage, in 6.3% moisture maize vs. 16%, and at 27°C storage temperature vs. 10°C. Oxygen depletion results allow estimation of days to 100% adult weevil mortality as a function of weevil infestation level, storage temperature and maize moisture for East Africa conditions. Key words: Maize storage, hermetic storage, Sitofilus zeamais, maize weevil, maize deterioration.

Argentine stem weevil (Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture

The Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoid Microctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide an L. bonariensis population dynamics baseline for any future work that aims to analyse the full effects of M. hyperodae on the weevil, now that equilibrium with the weevil host has been reached.The population dynamics of L. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-season L. bonariensis density was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis of L. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.In this study, the effect of the parasitoid biocontrol agent Microctonus hyperodae on L. bonariensis population dynamics was unclear, as the analysis covered a period when the parasitoid Microctonus hyperodae was introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.

Cooking oils and “Triplex” in the control of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in farm-stored maize

The uses of some cooking oils viz., noug oil, soybean oil, sunflower oil, corn oil and olive oil, and the reputedly non-toxic botanical “Triplex”, were evaluated against maize weevil, Sitophilus zeamais, in stored maize grain under local Ethiopian storage conditions in 2003. For comparison, an untreated sample and the synthetic insecticides, malathion 5% dust and Actellic 2% dust, at the recommended rates of 0.05% (w/w) were included. All the cooking oils tested had a significant toxic effect on the weevils in stored grains. The oil treatments showed significantly higher mortality of adult weevils at each sampling period compared with the untreated grains. The cooking oil treatments also significantly reduced weight loss and grain damage as compared with the untreated control. The Triplex treatment was of comparable effectiveness to the synthetic insecticides, causing high mortality of adult weevils, low-percentage grain damage and low-percentage weight losses. These promising oils and Triplex could be recommended for use as part of an integrated pest management program in stored maize, particularly at low levels of pest infestation and, in the case of cooking oils, for grain intended for home consumption.

Efficacy of the Entomopathogenic Fungus, Metarhizium anisopliae for Control of Maize Weevil Sitophilus zeamais Mots (Coleoptera-Curcuiionidae)

The virulence of eight isolates of entomopathogenic fungus, Metarhizium anisopliae, to the maize weevil, Sitophilus zeamais, was bioassayed in the laboratory. All the isolates tested were pathogenic to the weevil but to varying degrees. Isolates ICIPE 45 and 47 were superior to all other isolates in terms of mortality on adult weevils, protection of grains from damage and reduction in progeny production by the weevil. There were no significant differences between Pirimiphos-methyl-treated maize and maize treated with dry conidia of isolates ICIPE 45 and 47 in relation to adult weevil mortality, damage to maize grain and progeny emergence on maize at seven days post treatment. Both isolates persisted for more than six months on maize grain achieving up to 60 to 100% mortality at 7 days post treatment.

Comparison of Garlic and Lemon grass Products in the Control of Callosobruchus maculatus F. (Coleoptera: Bruchidae) on Stored Cowpea Grains

Powders of garlic (Allium sativum L.) bulb and lemon grass (Cymbopogon citratus Staph) stem were compared for their effectiveness against Callosobruchus maculatus F. on cowpea stored for three months. Garlic bulb powder at 2.5g, 5.0g and 10.0g per 100g cowpea grains gave 8.33%, 23.33%, 45.0% adult weevil mortality respectively in 24 hours; 50.0%, 56.66%, 75.0% adult weevil mortality respectively in 48 hours; while lemon grass stem powder of the same dosage caused 26.65%, 33.33%, 35.0% weevil mortality respectively in 24 hours and 56.65%, 66.66%, 68.33% mortality respectively in 48 hours. Garlic bulb and lemon grass stem powders significantly (P &lt; 0.01) reduced the oviposition and progeny emergence in all the treatment levels, compared with the control. However, lemon grass stem powders performed better than garlic bulb powder in F2 and F3 proqenies control and had better protection of cowpea grains. Seed viability and quality were unaffected by the treatments.

Mortality of the white pine weevil associated with silvicultural practices in jack pine plantations

A synthesis of white pine weevil (Pissodes strobi Peck) mortality caused by predation (insects, birds, and mammalian predators), crowding of pupae, and abiotic factors, acting under different stand conditions given by the type of reforestation, depth of the duff, distance from woody debris, and presence of competing vegetation is presented, based on a four-year study conducted in northeastern Ontario. The type of reforestation (planted vs. aerial seeding) did not influence mortality to immature weevils in the leaders from either bird predation, insect predators and parasitoids or crowding of pupae, but 16% more weevils died during winter in a planted than in a seeded stand suggesting that there was an effect of site condition or small mammal predation on overwintering adults in the duff. Over all conditions, overwintering mortality averaged 76-92% with small mammal predation representing about 5-13%. Site conditions which augmented small mammal populations and predation, such as proximity to woody debris and presence of competing vegetation, had no effect on overwintering mortality of the weevils. The most important factor influencing overwintering mortality was likely the depth of duff where an inverse relationship was observed between mortality and depth. Forest managers should address conditions of duff depth and small mammal predation to increase the already significant overwintering mortality of adult weevils in young jack pine stands. Key words: Pissodes strobi, silvicultural treatments, planted and seeded stands, competing vegetation, duff layers, small mammal predation, overwintering mortality

Influence of reforestation technique, slash, competing vegetation, and duff depth on the overwintering mortality of Pissodes strobi (Coleoptera: Curculionidae), the white pine weevil

We quantify the effects of reforestation technique (planted vs. seeded stands), distance from slash (beside slash vs. 100 m from slash), presence of competing vegetation (weed vs. weed-free patches), and depth of the duff on the overwintering mortality of the white pine weevil (Pissodes strobi Peck) in jack pine (Pinus banksiana) plantationsin northern Ontario, Canada. Open (control) and screened (exclusion) cages were used to separate mammalian predation from other overwintering mortality factors. Over 3 years, winter mortality of adult weevils ranged from 83 to 88% with mammalian predation significantly increasing adult mortality by 5–13%. More weevils died over winter in a planted stand (92%) than in a seeded stand (76%), although subsequent damage was similar in both stands. The distance from slash and the presence of competing vegetation had no effect on the overwintering mortality of weevils. More small mammals were found in patches with competing vegetation than without, which was associated with higher levels of weevil predation. The total number of weevils dying was inversely related to the depth of the duff. However, this difference was not significant because of a high variation within treatments. The implications of these results for forest management and the reduction of white pine weevil populations are discussed.

Predation and overwintering mortality of the white pine weevil, Pissodesstrobi, in planted and seeded jack pine

Predation by birds and insects and overwintering mortality of the white pine weevil, Pissodesstrobi Peck, were examined in planted and seeded stands of jack pine (Pinusbanksiana Lamb.) in northern Ontario to develop recommendations for management. No significant difference was found in weevil damage to the stand and in mortality of weevils due to natural enemies between planted and seeded stands. On average, 7.3 ± 0.3 (mean ± 1 SE) weevils emerged as adults from dead terminals. Birds consumed up to 6.4% of late-larval and pupal weevils in planted stands and up to 8.9% in seeded stands. More weevils emerged from screened than from unscreened leaders, indicating a significant mortality of larvae and pupae, presumably owing to insect predators and parasitoids and high density of pupae. Overwintering mortality of adult weevils was 92% in the planted and 76% in the seeded stand. Mammalian predation significantly reduced survival of overwintering weevils. Factors related to other silvicultural treatments, such as the presence of weeds, may be affecting the survival of Pissodesstrobi and the susceptibility of Pinusbanksiana stands to Pissodesstrobi infestation. The manipulation of both mammalian predation and overwintering sites should be emphasized in the management of P. strobi in Pinusbanksiana plantations.

The Susceptibility of some maize varieties to Sitophilus Zeamais mots (Coleoptera: Curculionidae)

Four maize varieties, 8321–21-W, DMR-LSR-W, ACR-83TZUT-W and TZB were simultaneously fed to Sitophilus zeamais in a completely randomized design. Susceptibility was assessed on such parameters as weight loss of grains caused by the weevil infestation, number of progenies at 42 days after infestation and the percentage of damaged kernels. The least susceptible in terms of loss of weight of grains was TZB. Losses in the other three were not significantly different at 5% level (P ≻ 0.05). The least percentage mortality of adult weevils and the highest number of punctured kernels were observed in var. 8321–21-W (48%), 27 kernels respectively while var. DMR-LSR-W had the highest mortality score (80%) and ranked second in the total number of kernels punctured (13). Details of the description of maize varieties used and the analysis of damage caused by the weevil are discussed in the paper.