Cold hardiness and overwintering survival of the cabbage seedpod weevil,Ceutorhynchus obstrictus

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a serious pest of brassicaceous crops in temperate regions and a chronic member of the pest complex that attacks canola in Canada. We conducted several laboratory and field experiments to quantify winter survival and its role in the population dynamics of this insect. We estimated the supercooling point of the weevil at ?7 °C and its survival over 8 weeks decreased significantly at ?5 °C relative to 5 °C, but extending the overwintering period at 5 °C to 18.5 weeks had no effect on mortality. Cumulative sub‐freezing degrees estimated from air temperature, and especially from soil temperature, were highly correlated with weevil survival. Our linear regression model predicted poor survival of the weevils in typical winters in northern Alberta. Our results indicate that if milder winters prevail, as predicted by global warming, there is potential for the weevils to establish and become a serious pest in northern canola‐growing regions of Canada.     

Overwintering of annual bluegrass weevils, Listronotus maculicollis, in the golf course landscape

Annual bluegrass weevil, Listronotus maculicollis (Dietz) (Coleoptera: Curculionidae), adults overwinter in protected areas but their life cycle is completed on highly maintained turfgrass. To better target control tactics on affected golf courses, we need to understand the relationship between overwintering and developmental habitats. Our objectives were to identify factors that influence overwintering site selection and to gather evidence of directional movement. Surveys of natural field populations were conducted in early spring over 2 years to test how abundance of overwintered adults depends on microhabitat (surface composition) and distance from the developmental habitat. The influence of microhabitat on overwintering preference and success was further tested in a multiple‐choice and no‐choice field experiment by relocating overwintering weevils into experimental arenas where four microhabitats were presented together or singly. The timing and direction of dispersal by walking adults was assessed using paired linear pitfall traps. Results showed that adults could overwinter up to 60 m from the fairway and 10 m into the woods. They were most abundant near the tree line; none were detected within 5 m of the fairway. Microhabitat had a significant effect on abundance in 1 year, being highest in mixed tree litter followed by moss, high‐cut grass, and pine litter. Under multiple‐choice conditions, high‐cut grass was preferred over low‐cut grass and leaf litter, followed by pine litter. Pitfall trap captures showed a peak of activity in the spring, and at one site this was directional toward the fairway. There was no directionality or increase in activity in the fall. Based on these results, a new conceptual model of flux between habitats is proposed based on orientation of flying adults to defined tree lines. Defining this behavior will strengthen our ability to target control tactics in space and time against this major turf pest.     

Cold tolerance of the montane Sierra leaf beetle,Chrysomela aeneicollis

Small ectothermic animals living at high altitude in temperate latitudes are vulnerable to lethal cold throughout the year. Here we investigated the cold tolerance of the leaf beetle Chrysomela aeneicollis living at high elevation in California’s Sierra Nevada mountains. These insects spend over half their life cycle overwintering, and may therefore be vulnerable to winter cold, and prior studies have demonstrated that survival is reduced by exposure to summertime cold. We identify overwintering microhabitat of this insect, describe cold tolerance strategies in all life stages, and use microclimate data to determine the importance of snow cover and microhabitat buffering for overwinter survival. Cold tolerance varies among life history stages and is typically correlated with microhabitat temperature: cold hardiness is lowest in chill-susceptible larvae, and highest in freeze-tolerant adults. Hemolymph osmolality is higher in quiescent (overwintering) than summer adults, primarily, but not exclusively, due to elevated hemolymph glycerol. In nature, adult beetles overwinter primarily in leaf litter and suffer high mortality if early, unseasonable cold prevents them from entering this refuge. These data suggest that cold tolerance is tightly linked to life stage. Thus, population persistence of montane insects may become problematic as climate becomes more unpredictable and climate change uncouples the phenology of cold tolerance and development from the timing of extreme cold events.     

Phenological analysis of spring colonisation of apple trees by Anthonomus pomorum

Adult apple blossom weevils, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), leave their overwintering sites within and outside orchards to colonise apple trees in early spring. This study was conducted to characterize the temporal pattern of spring colonization of apple trees by overwintered weevils in relation to climatic conditions and apple bud stages, based on multiple mark-release-recapture experiments and field observations of foraging activities of weevils. The process of spring colonization of apple trees by overwintered weevils was related to thermal time totals above 0 °C. The dispersal into orchards initiated when the thermal time totals reached 161±27 (s.d.) degree-days (DD) calculated from January 1, or 117±16 DD from February 1. The daily dispersal speed of individual weevils within orchards was determined primarily by the maximum daily temperature, whereas crawling, feeding, and mating activities of weevils on apple trees were influenced by the mean evening temperature between 18:00 and 22:00 hours. On the other hand, the spring colonization of overwintered weevils was not synchronized with any specific apple bud stage, though the level of female foraging and reproductive activities on apple trees was related to apple bud stages. The overwintered weevils initiated dispersal into orchards over a wide range of bud developmental stages from little silver greenish tip B (51) to the mouse-ear stage C3 (54). These findings are discussed in relation to the ecology and pest management of this insect.     

Evaluation and implications of Andean potato weevil infestation sources for its management in the Andean region

The Andean potato weevil Premnotrypes suturicallus Kuschel (Coleoptera: Curculionidae) is one of the most damaging potato (Solanum spp.) pests in the Andes. The objective of this study was to get a better understanding of weevil infestation sources and its distribution in potato fields as well as on the effect of potato cropping intensity and farmers’ harvest practices on weevil infestation to provide better clues for its management. For this purpose, a methodology was developed to assess weevil field densities in potato. A Taylor’s power law indicated that 177 and 69 samples are necessary to assess low (0.5 weevils/m²) and high (5 weevils/m²) weevil densities for a moderate reliability or precision level (D = 0.5). In potato fields, overwintering weevil densities were highest at field borders with 3.5 weevils/m² at a distance of <2.5 m compared to 0.7 weevils/m² at distances >10 m from the field border. No effects of time of harvest could be detected on soil overwintering weevil densities. The quantification of the larval density per potato plant after harvest showed that fields after 2‐year potato rotations had eight times more overwintering weevils compared to 1‐year rotations. Weevil infestation sources were mainly potato fields with the highest infestation (89%) followed by olluco (Ullucus tuberosus) and oat (Avena sativa) fields having volunteer potato plants (35%). The results confirm and support previous assumptions about the importance of the cropping systems for Andean potato weevil infestation and management. The confirmation that weevils do not occur or only in neglected numbers on fallow fields supports the use of plastic barriers to effectively exclude migrating flightless adult weevils to potato fields cultivated after fallow. The distribution of overwintering weevils indicates that farmers could concentrate efforts to control adult weevils mainly to the first meters of potato fields.     

Evidence for a substantial host‐use bottleneck following the invasion of an exotic,polyphagous weevil

1. The successful establishment of novel plant–insect interactions may depend on the availability of suitable hosts, which itself is influenced by the inherent flexibility of the herbivore for the native plants in its new range. The polyphagous beech leaf mining weevil, Orchestes fagi L., is a recent invader to eastern Canada, and while beech is a primary host, it remains unclear the extent to which it might also utilise co‐occurring secondary hosts, as has been observed in its native European range. 2. A combination of field and laboratory feeding trials were used to quantify weevil secondary host use. Based on its expansive native host range in Europe, it was predicted that American beech (Fagus grandifolia Ehrh.), as well as several additional plant species, would be susceptible to weevil damage. 3. Contrary to this prediction, weevil feeding was almost entirely exclusive to beech in both the field and laboratory feeding trials. This result is further supported by field observations that revealed an absence of weevils and eggs on species other than beech. In general, the lack of pre‐diapause feeding on any alternate host species represented an extreme departure from feeding habits observed within the native range. 4. Overall, this host‐use bottleneck suggests that the adoption of a novel primary host by O. fagi, in this case American beech, may remove the normal requirement for secondary hosts and suggests a significant departure from native feeding habits with possible consequences for related life‐history parameters such as overwintering survival and fecundity.     

The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

• 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi‐voltine, with a 2‐year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate.
• 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures.
• 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day‐degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures.
• 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle.
• 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.

     

Effects of Rhinoncomimus latipes on the growth and reproduction of Persicaria perfoliata,an invasive plant in North America

Native to Asia, mile-a-minute Persicaria perfoliata, is an invasive weed in North America, and the weevil Rhinoncomimus latipes is a host-specific insect agent which occurs widely in China. We conducted a common garden experiment to compare P. perfoliata plant responses of native and invasive populations to herbivory by the weevils from different origins. We found weevils from Hunan, Hubei and Heilongjiang Provinces had strong, moderate and weak ability to suppress host plant, respectively. Weevils from Hunan and Hubei Provinces had stronger impact on the growth of both native and invasive plant populations than the weevil from Heilongjiang Province. The losses in seed output of invasive plants were also significantly greater than natives in the weevil treatments. Our results suggested that the weevil population from Hunan Province may be the most suitable for the control of mile-a-minute, while the population from Heilongjiang Province may be the least suitable due to climate matching.     

Improving phenological forecasting models for rape stem weevil,Ceutorhynchus napi Gyll., based on long‐term multisite datasets

New threshold‐based models to predict the start of invasion by the stem‐boring pest, the rape stem weevil (Ceutorhynchus napi Gyll.) of winter oilseed rape (Brassica napus L.), were developed and compared to published models using long‐term datasets on weather and weevil phenology from experimental locations in Germany and Luxembourg. Threshold values for daily records of maximum air temperature, mean soil temperature, sunshine duration and total precipitation were adjusted to local conditions on the date of first weevil migration in spring. Mean error and the root mean squared error were used to assess model quality, where the error is defined as the number of days between predicted and observed arrival of weevils on the crop (regardless of sign). Best model results predicted first crop invasion by rape stem weevil when the thresholds of daily maximum air temperature ≥7.8°C, mean soil temperature ≥6.6°C, daily total precipitation ≤1.0 mm and sunshine duration ≥1 h were matched. This model takes into account meteorological variables likely to influence conditions at the overwintering site of the weevils in the soil, as well as variables that may limit weevil flight. Adjusted air temperature threshold values were consistently lower for Luxembourg sites than for those optimized for Germany. A simple model relating the date of first weevil invasion to accumulated daily maximum air temperature above 0°C (from 1 January) was also evaluated. This proved less suitable for forecasting crop invasion by C. napi. We suggest that phenological models using locally adjusted meteorological‐based thresholds have the potential to offer sufficiently accurate forecasts of first immigration flights by C. napi for appropriate timing of insecticide application. In addition, the developed models are suitable tools to be used in climate change impact studies.     

Early-season aerial adult colonization and ground activity of pea leaf weevil (Coleoptera: Curculionidae) in pea as influenced by tillage system

The pea leaf weevil, Sitona lineatus (L.) (Coleoptera: Curculionidae), is an important pest of pea, Pisum sativum L., in northern Idaho. Previous research revealed greater relative pea leaf weevil abundance and feeding damage in peas grown using conventional-tillage compared with no-tillage practices. However, the effects of tillage practices on early season colonization and activity by the pea leaf weevil on pea are not fully understood. Aerial traps and pitfall traps were used to assess adult colonization and relative density of adult pea leaf weevil into conventional-tillage and no-tillage pea in northern Idaho during 2005 and 2006. Feeding damage to the crop also was evaluated. During both years, aerial traps captured more pea leaf weevil in May, when crop establishment and early growth occurred, than in later months. Significantly more adult pea leaf weevils were captured in aerial traps in conventional-tillage than in no-tillage plots in May of both years. Significantly more pea leaf weevil were captured in pitfall traps in conventional-tillage plots than in no-tillage plots during the period immediately after peak aerial adult colonization in late May and early June. Crop feeding damage was significantly greater in conventional-tillage than in no-tillage plots in late May and early June. The patterns suggest that more adult pea leaf weevil colonize conventional-tillage pea than no-tillage pea. Pea plants in conventional-tillage emerged earlier and were larger than those in no-tillage during the pea leaf weevil colonization period, possibly accounting for the differences in colonization rates. This leads to greater early season pea leaf weevil infestation of conventional-tillage plots at a critical period for pea development that might ultimately influence crop yield.     

Impact in quarantine of the galling weevil Lepidapion argentatum on shoot growth of French broom (Genista monspessulana), an invasive weed in the western U.S.

In weed biocontrol, there is a need for pre-release efficacy assessments for potential agents. Genista monspessulana ((L.) L. A. S. Johnson (Fabaceae), French broom) is an invasive perennial shrub in the western U.S. The galling weevil Lepidapion argentatum Gerstaecker is a potential biocontrol agent. The impact of increasing weevil density on galling damage, plant height, width, leaf damage, and relative growth rate (RGR) was assessed in greenhouse experiments on two to three-month-old seedlings infested with either one or three weevils. Infestation by three female weevils caused 48% more galls producing 27% more larvae than did infestation with one female while causing only 1% leaf damage and no difference in total leaf area. Infestation with multiple weevils caused a 55% and 29% decrease in plant height and canopy width respectively, while single-weevil infestation decreased height by 32% and width to the same degree as for multiple weevils. The RGR of seedlings infested with three weevils was three times slower than the controls, while growth was reduced 2-fold by single-weevil infestation. Reductions in plant size and growth rate induced by weevil galling could reduce plant competitive survival to reproduction and also plant population dispersal as seedlings. Our results suggest that L. argentatum has the potential to cause impact to French broom seedlings if released in the invasive range.     

稻水象甲越冬成虫的耐寒力测定

测定了浙江乐清 (北纬 2 8 1 4°,东经 1 2 0 94°)稻水象甲LissorhoptrusoryzophilusKuschel越冬成虫的耐寒力 ,从 1 1月下旬至 3月下旬平均过冷却点温度为 -1 5 3～ -2 1 2℃ ,结冰点温度为 -1 4 0～ -1 8 6℃。结合发生地气温条件 ,讨论了该地冬春季低温对该虫越冬群存活的影响。     

Phenology and temperature‐dependent development of Ceutorhynchus assimilis,a potential biological control agent for Lepidium draba

Lepidium draba (Brassicaceae) is a major concern for agriculture and biodiversity in the western United States. As current control methods do not provide long‐term, sustainable solutions, research has been conducted to find biological control agents. Ceutorhynchus assimilis is one of the currently investigated candidates. Known as oligophagous in the literature, a specialist clade of this root‐galling weevil exists in southern Europe. This raised the question of its ability to survive in colder climates in the target range. We investigated the phenology of C. assimilis in the field in southern France (specialist clade) and Romania (generalist clade) and measured various temperature‐dependent parameters in the laboratory. In both ranges, weevils were univoltine. Oviposition in autumn started later in France compared to Romania, while mature larvae exited galls (to pupate in the soil) earlier the following year. On average, 25% and 32% of galls from France and Romania were completely below the soil surface, respectively, and this appeared to depend on soil substrate. Weevils transported from France to Romania were able to develop, but at a much lower rate than Romanian weevils. Mortality of overwintering larvae of both clades increased with decreasing temperature and exposure time. At ?5°C, lethal times Lt₅₀ and Lt₉₅ were 15 and 42 days for the specialist clade and 26 and 72 days for the generalist clade. A higher proportion of third instar larvae compared to first and second instar larvae survived. Pupation time at different temperatures did not differ between weevils from France or Romania. A climate match model (comparing winter temperatures) indicated that the specialist clade of C. assimilis from France has the potential to establish in some parts of the target range (e.g. Washington, Oregon, California). However, temperature extremes and winters without snow cover will likely limit its establishment unless rapid adaptive evolution takes place.     

Reproductive potential of overwintering, F1, and F2 female boll weevils (Coleoptera: Curculionidae) in the Lower Rio Grande Valley of Texas

The feeding and oviposition activity of overwintering boll weevils, Anthonomus grandis grandis (Boheman), and seasonal fluctuations in development, survival, and reproduction of progeny of overwintering and first- and second-generation boll weevil females were determined in the laboratory at 27 degrees C, 65% RH, and a photoperiod of 12:12 (L:D) h. During the cotton-free period in the Lower Rio Grande Valley, female boll weevils without access to cotton resorb their unlaid eggs and enter reproductive diapause. However, when they were provided daily with greenhouse-grown cotton squares, commencement of oviposition began after 7, 15, or 20 d, depending on when they were captured. Females captured later in the winter fed longer before laying eggs than those captured in the early fall, suggesting that it may take females longer to terminate diapause the longer they have been dormant. The rate of feeding by females was significantly less during the winter months, and this may have affected the rate of diet-mediated termination of dormancy. Females of the first and second generations after the overwintering generation produced a significantly higher percentage of progeny surviving to adulthood and a higher proportion of these progeny were females. Offspring development time from overwintering female parents was significantly longer than that from first and second generations under the same laboratory conditions. The total number of lifetime eggs produced by females of the second generation during the cotton-growing season were approximately 9.9-fold higher than for overwintering females and 1.5-fold higher than for first-generation females. Life table calculations indicated that the population of second-generation boll weevils increased an average of 1.5-fold higher each generation than for females of the first generation and 22.6-fold higher than for overwintering females. Our data showed variation in boll weevil survival, development, and reproductive potential among the overwintering and first- and second-generation females, suggesting inherent seasonal fluctuations in these parameters.     

Selection of hibernation sites by Anthonomus pomorum: preferences and ecological consequences

The apple blossom weevil, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), has a long period of aestivo-hibernation in the adult stage lasting from summer to early spring of the following year. Potential hibernation sites within an apple orchard consist of high-stem rough-bark trees or dwarf smooth-bark trees. Field release-recapture experiments in 2 consecutive years showed that 64 and 47% of the weevils remained in the vicinity of the release sites in an area of high-stem trees and dwarf trees, respectively. The dispersing weevils moved over an average distance of 5.5 m in the dwarf tree area, as compared to 3.8 m in the high-stem tree area. The prevalent direction of dispersal was along tree rows in both areas. Some weevils displayed, after release in mid-July, a directional dispersal to the adjacent forests. Others, released in the dwarf tree area, dispersed towards the area of high-stem rough-bark apple trees. Experiments simulating various hibernation sites demonstrated that the litter of dry leaves was the most preferred overwintering shelter, yielding a relatively high survival rate. Branches with rough bark ranked second, while branches with smooth bark, grass and pure soil were not favourable for overwintering. Flight tendency in newly emerged weevils of summer generation was significantly higher in June/July than in August/September. This corresponds to the dispersal behaviour in the field. The timing of spring colonisation of apple trees was similar for weevils overwintering within the orchard and for those from outside. These results suggest that modern, dwarf apple orchards offer unfavourable conditions for overwintering, but that the relatively small proportion of weevils which manage to reach the adjacent forests find optimal hibernation sites there.     

Nutrition,sex and season contribute to variation in fat and glycerol levels in the long‐lived moth Caloptilia fraxinella

The ash leaf cone roller Caloptilia fraxinella Ely (Lepidoptera: Gracillariidae) is an invasive leaf‐mining moth pest of horticultural ash Fraxinus spp. in the Canadian Prairie Provinces. Caloptilia fraxinella overwinter as adults in reproductive diapause and mating occurs after overwintering in the spring. The effect of a carbohydrate food source on fat and glycerol reserves throughout the long adult life stage of this moth is investigated. Insects collected as pupae are given access to either water or sugar water upon adult eclosion. Moths held under the different feeding regimes are sampled before (summer and autumn) and after overwintering in the spring. Analysis of either glycerol or lipid content is conducted for male and female moths from each collection period. Both moth weight and glycerol concentration are affected by moth sex, food regime and season of collection. Although female moths are heavier than males, a higher glycerol concentration occurs in males. Moths fed sugar are heavier and have a higher glycerol concentration than water‐fed moths late in reproductive diapause and after overwintering. Moths collected in the spring after overwintering are lighter and have a lower glycerol content than moths collected before winter. There is a significant influence of feeding regime and season on moth body lipid content, with sugar‐fed moths having more fat than water‐fed moths; however, this difference is smaller in the summer than the autumn or spring. An initial understanding of the overwintering biology and diapause of this pest is provided in the present study.     

Overwintering strategy of two weevils infesting three gorse species: When cold hardiness meets plant-insect interactions

The cold hardiness of two closely related weevil species, Exapion ulicis and E. lemovicinum was studied in relation to their life cycles. These two seed-eating weevils reproduce on Ulex plant species with different fruiting phenologies. E. ulicis lays eggs in spring and overwinters as an adult while E. lemovicinum lays eggs in autumn and overwinters as a larva. Adult weevils were collected in natural populations of Brittany (Western France) and characterized with morphological and molecular tools before experiments. We showed that both weevil species exhibited low supercooling points (SCPs) with mean seasonal values below −17 °C. Fresh mass, moisture content and sex were not correlated to supercooling ability. Weevils died upon freezing and the lower lethal temperatures (LLT) were within the range of SCP, indicating that both species are freezing intolerant. Comparison between species for SCP, LLT and survival to exposure at −8 °C in winter showed a higher cold resistance for E. ulicis than for E. lemovicinum. In addition, the seasonal evolution of cold hardiness differed depending on the species. These features suggest that response to cold of weevils is linked to their life cycles, and thus to the life history of their host plants.     

Leaf scarring by the weevils Neochetina eichhorniae and N. bruchi enhances infection by the fungus Cercospora piaropi on waterhyacinth, Eichhornia crassipes

Additive or synergistic effects among introduced and native insect and plant pathogen agents are necessary to achieve biological control of waterhyacinth (Eichhornia crassipes), a globally damaging aquatic weed. In field plots, plants were infested with waterhyacinth weevils (Neoechetina bruchi and N. eichhorniae) and leaves were scarred by weevil feeding. Subsequent infection by the fungal pathogen Cercospora piaropi caused necrotic lesions to form on leaves. Necrosis development was 7.5- and 10.5-fold greater in plots augmented with both weevils and C. piaropi and weevils alone, respectively, than in plots receiving only C. piaropi. Twenty-four days after weevil infestation, the percentage of laminar area covered by lesions on third-youngest and oldest live leaves was elevated 2.3–2.5-fold in plots augmented with weevils. Scar density and necrosis coverage on young leaf laminae were positively correlated, even though antipathogenic soluble peroxidases were elevated 3-fold in plots augmented with weevils alone or weevils and C. piaropi. Combined weevil and fungal augmentation decreased shoot densities and leaves per plant. In a no-choice bioassay, weevil feeding on oldest but not young leaves was reduced 44 two weeks after C. piaropi inoculation. Protein content and peroxidase activities were elevated 2–6-fold in oldest leaves three weeks after inoculation. Augmentation with both waterhyacinth weevils and C. piaropi led to the development of an additive biological control impact, mediated by one or more direct interactions between these agents, and not plant quality effects.     

Common subtropical and tropical nonpollen food sources of the boll weevil (Coleoptera: Curculionidae)

It is known that substantial boll weevil, Anthonomus grandis grandis Boheman, individuals can survive mild subtropical winters in some habitats, such as citrus orchards. Our study shows that endocarp of the fruit from prickly pear cactus, Opuntia engelmannii Salm-Dyck ex. Engel.; orange, Citrus sinensis L. Osbeck.; and grapefruit, Citrus paradisi Macfad., can sustain newly emerged adult boll weevils for >5 mo, which is the duration of the cotton-free season in the subtropical Lower Rio Grande Valley of Texas and other cotton-growing areas in the Western Hemisphere. Cotton, Gossypium hirsutum L., and the boll weevil occur in the same areas with one or all three plant species (or other citrus and Opuntia species that might also nourish boll weevils) from south Texas to Argentina. Although adult boll weevils did not produce eggs when fed exclusively on the endocarps of prickly pear, orange, or grapefruit, these plants make it possible for boll weevils to survive from one cotton growing season to the next, which could pose challenges to eradication efforts.     

Spring colonisation of orchards by Anthonomus pomorum from adjacent forest borders

The early-season dispersal of the overwintered apple blossom weevil, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), is a crucial stage in the colonisation of dwarf apple orchards adjacent to forests. We have conducted release-recapture studies with 1700 to 4000 marked weevils at two orchard sites in Switzerland over 2 years to characterise the spatial and temporal pattern of the dispersal process. The dispersal and colonisation of orchards in spring by overwintered weevils is dependent upon the prevailing temperature.An orientated dispersal from the forest border to the centre of the orchard was observed consistently, irrespective of the angle of the apple tree rows with respect to the forest border or of climatic conditions. The average dispersal distance of the weevils was 19 m. Approximately one third of the weevil population remained on the first tree encountered, the remainder of the population moved over short distances mainly along the tree rows. This dispersal pattern led to a strong edge effect with higher numbers of weevils occurring at the edges adjoining the forests as compared to the centre of orchards. The relevance of these findings to population dynamics and management of the pest is discussed.