Comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin is pathogenic to C. caryae. One approach to managing C. caryae may be application of B. bassiana directed toward adult weevils as they emerge from the soil to attack nuts in the tree canopy. Our objective was to compare different application methods for suppression of C. caryae adults. Treatments included direct application of B. bassiana (GHA strain) to soil under the tree canopy, soil application followed by cultivation, soil application in conjunction with a cover crop (Sudan grass), direct application to the tree trunk, and application to the trunk with an UV radiation-protecting adjuvant. The study was conducted in a pecan orchard in Byron, GA, in 2005 and 2006. Naturally emerging C. caryae adults, caught after crawling to the trunk, were transported to the laboratory to determine percentage mortality and signs of mycosis. When averaged over the 15-d sampling period, weevil mortality and signs of mycosis were greater in all treatments than in the nontreated control in 2005 and 2006; >75% average mortality was observed with the trunk application both years and in the trunk application with UV protection in 2005. Results indicated trunk applications can produce superior efficacy relative to ground application, particularly if the ground application is followed by cultivation. Efficacy in the cover crop treatment, however, did not differ from other application approaches. Future research should focus on elucidating the causes for treatment differences we observed and the extent to which B. bassiana-induced C. caryae mortality reduces crop damage.     

Monitoring the dynamics of orchard colonisation by Anthonomus pomorum in spring

Overwintered adult apple blossom weevils, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), colonise apple trees, Malus domestica Borkh. (Rosaceae), in early spring. Information gained from a suitable monitoring technique could serve as a guide to determining the accurate timing for control measures. To assess tree colonisation by flight and crawling, Plexiglas flight traps and commercial screen traps developed for different curculionid species were used. Refuges were mimicked by a newly designed shelter trap based on transparent bubble wrap. The trap catches were contrasted to the limb jarring technique. Microclimate and weather conditions were determined over a trial period of one and a half months. The shelter traps caught a high number of weevils irrespective of weather conditions, and thus performed better than both flight and screen traps. The temperature level within the shelter traps was slightly, but significantly, higher than on the trunk, indicating that weevils exploit microclimatic differences and occupy thermally favourable refuges. The seasonal culmination of colonisation as determined by shelter traps coincided with that as determined by the two methods used to monitor weevil movement towards host trees (flight traps and screen traps). The data indicated that not only flight, but also crawling as quantified by the screen traps contributes substantially to spring colonisation. Captures by all three types of traps over the spring season were significantly positively correlated with each other, but in most respects not with the results of the limb jarring. We conclude that the newly designed shelter trap will be useful for accurately monitoring the seasonal course of colonisation and holds promise for determining the timing of interventions.     

Vertical and horizontal movements of Fuller's rose weevil (Coleoptera: Curculionidae) in Australian citrus groves

Fuller's rose weevil (FRW; Asynonychus cervinus (Boheman)) is a pest of quarantine concern in many Asian markets for Australian citrus. We investigated vertical (tree climbing) and horizontal movements (inter‐tree movements) of FRW adults in a citrus orchard during 2009–2011 with mark‐recapture experiments. Trunk traps were used to intercept tree‐climbing adults. The results showed that the majority of the adults released on the foliage stayed in the canopy, however considerable numbers did drop and some dropped multiple times. The rate of drops appeared to be fixed, independent of how many times the weevils had dropped before. Inter‐tree movements of adults in the canopy occurred mainly within rows, probably because of touching foliage between within‐row neighboring trees. Movement directions on the ground were more random, when reliance on touching foliage was not necessary. According to fitted dispersal equations, the average dispersal distance was 38 m for weevils released on foliage and 127 m for those released on the ground. Trunk banding with chemicals is an important control tactic for FRW, and based on our results, chemicals should be applied at a high enough rate (or in a wide enough band) to ensure the weevils are killed by a single crossing. For maximum reductions of FRW populations in citrus, control actions should be applied not only to infested blocks but also to neighboring blocks in the orchard.     

The role of Palmyra palm trees (Borassus flabellifer) and sand fly distribution in northeastern India

Visceral leishmaniasis (VL), known as Kala-azar in India, is a parasite transmitted by the bite of the sand fly vector Phlebotomus argentipes. Published information on the species indicates it is a poor flyer, mainly hopping and gliding. This study describes the vector as more arboreal than previously documented. Data collected indicate the ability of P. argentipes and Sergentomyia spp to attain vertical heights in Palmyra palm trees Borassus flabellifer up to 18.4 m above ground level. To determine if sand flies were either climbing the tree trunk to rest in the canopy or flying, sticky traps were set around the tree trunk and checked for captures overnight. CDC traps set in the palm tree canopy resulted in the capture of 5,067 sand flies, 3,990 of which were P. argentipes. Traps were set during daylight hours to determine if sand flies remained and rested in the canopy. A total of 128 sand flies were trapped over 29 trap days in the palm trees. With the CDC traps, 130 P. argentipes and no Sergentomyia spp were captured. The converse was true for the sticky traps set around tree trunks 3 m below the CDC traps. Of the 105 sand flies collected, only one was P. argentipes and 104 were Sergentomyia spp. As reported elsewhere, this indicates Sergentomyia spp tend to climb and hop, wheareas P. argentipes are capable of longer and more sustained flight. Data presented herein suggest that P. argentipes is more exophylic and exophagic than previously reported. These findings have implications for sand fly control.     

Tree Height Influences Flight of Lesser Peachtree Borer and Peachtree Borer (Lepidoptera: Sesiidae) Males

Capture of male lesser peachtree borer, Synanthedon pictipes (Grote & Robinson), and peachtree borer, S. exitiosa (Say) (Lepidoptera: Sesiidae), in pheromone traps positioned from 0 m to 6 m above ground was affected by surrounding tree height. In a peach orchard with a 3 m canopy height, more S. pictipes were captured within the canopy zone at 1.8 m than above at 5.5 m. Trap capture was similar for S. pictipes in a mating disruption orchard with more caught at 2 m than at 4 m or 6 m. Capture at 1.8–5.5 m in mixed deciduous woods, with an average canopy height of 22 m, was not significantly different. In orchards, more S. exitiosa were captured at 1.8 m rather than at 5.5 m but no difference was detected in numbers captured from 0 m to 5.5 m in mixed deciduous woods. In a peach-pecan interplanted orchard, where pecan trees were three times taller but only one-ninth the density of peach, capture of both species was similar to capture in peach orchards when traps were entirely surrounded by peach. However, when traps were adjacent to a single, taller non-host pecan tree, capture was similar to mixed deciduous woods. These data suggest that habitat structure supersedes presence/absence of host plants affecting vertical flight activity of male S. pictipes and S. exitiosa.     

Development and comparison of trunk traps to monitor movement of Halyomorpha halys nymphs on host trees

Halyomorpha halys Stål (Hemiptera: Pentatomidae) has recently become a major orchard pest in the Mid‐Atlantic, USA. Large H. halys populations can develop on wild tree hosts adjacent to orchards, posing an ongoing threat to fruit. Adults and nymphs feed on tree fruit, causing economic injury. Understanding the seasonal patterns of nymphal host use among trees at the orchard‐woodland interface may aid the development of integrated pest management strategies for this pest. In laboratory and field experiments, modified versions of published trap designs – ‘Circle’, ‘Hanula’, ‘M&M’ (after Moeed & Meads) traps – were compared for their effectiveness for capturing H. halys nymphs walking up and down tree trunks. In the laboratory, second instars were released at the top and bottom of ailanthus (tree of heaven), Ailanthus altissima (Mill.) Swingle (Simaroubaceae), logs and captures were recorded after 24 h. Circle and M&M traps, respectively, were most effective for capturing nymphs walking up and down. In the field, traps were deployed on ailanthus trees next to apple orchards and captures were recorded weekly from 24 July to 11 September 2013. As in the laboratory, Circle and M&M traps captured the greatest number of upward‐ and downward‐walking nymphs. Hanula traps were least effective in both experiments. In the field, 88% of total captures were of nymphs walking up trees. This was at least partially explained by behavioral assays in the laboratory demonstrating that nymphs exhibited negative gravitaxis and positive phototaxis. Stage‐specific trends in captures of instars walking up during field sampling were observed. These results suggest that trunk traps can be used to address important ecological questions about seasonal patterns of host use by H. halys nymphs.     

Effect of trap position, habitat, and height on the capture of pepper maggot flies (Diptera: Tephritidae)

Trapping results indicate that pepper maggot, Zonosemata electa (Say), flies occupy tree canopies adjacent to fields when not on host plants. Several in- and near-field trap positions were used to find a reliable monitoring system for adult pepper maggots. Traps baited with liquid ammonium hydroxide (Stills-style trap), hung in the canopy of trees on the edges of pepper fields, caught significantly more Z. electa flies than when positioned lower along the treeline or in the field. In a second experiment, significantly more pepper maggot flies were captured in sugar maples compared with choke cherry trees, which indicates a pest preference for certain nonhost habitats. The lowest trap height tested (2.1 m) failed to capture Z. electa flies in either tree species when the pest population level was low. These studies demonstrated that pepper maggot flies can be reliably detected with Stills-style traps positioned at approximately 6.4 m height within the canopy of sugar maple trees adjacent to pepper fields. Fruit oviposition scars also are useful site-specific indicators of pepper maggot presence/absence and may aid in determining if insecticide applications are necessary and in timing sprays.     

Assessing ectomycorrhizal fungal spore banks of truffle producing soils with pecan seedling trap-plants

Background and Aims

Recently, the truffle species Tuber lyonii Butters was found to be dominant in ectomycorrhizal (EcM) fungal communities of cultivated pecan (Carya illinoinensis (Wangenh.) K. Koch). Many truffle fungi exhibit the trait of effectively colonizing plant roots via spores. We hypothesized that T. lyonii would be well represented in the spore bank of pecan orchard soils where it is found.

Methods

We used axenically-grown pecan seedlings as trap-plants to bait for EcM associates in soils collected beneath truffle-producing pecan trees. EcM fungi on seedlings were characterized through rDNA sequencing and were compared to EcM communities of adult trees in these orchards.

Results

Tuber lyonii mycorrhizas were well formed on seedlings inoculated with truffle spores, but were limited to just a few of the trap-plants grown in field soils. We compared EcM communities of adult pecan orchard trees to those on trap-plants and found distinct communities on each, with a high degree of similarity at the ordinal but not species level.

Conclusions

Although species of Pezizales are abundant in pecan EcM communities and as propagules in their soil spore banks, only a low level of T. lyonii was detected in soil spore banks beneath orchard trees naturally colonized by T. lyonii. Other factors including land-use history or orchard management may better explain this truffle species presence and abundance in pecan EcM communities.

     

Movement of plum curculio adults toward host trees and traps: flight versus walking

Adult plum curculios, Conotrachelus nenuphar (Herbst), were dislodged from branches of apple trees by tapping on 14 days between blossom petal fall and 3 weeks thereafter. They fell onto a small square of framed white cloth that was quickly but carefully moved to a position beneath or adjacent to the canopy of another apple tree.There, adults were observed for 50-min periods from 0800–1950 h for propensity to fly from or walk off the cloth or move to hide beneath foliage on the cloth. At each position, the mean time from observation initiation until flight, walking off or hiding did not differ significantly among these behaviors (averaging 21–30 min), but significantly more flew (31–40%) than crawled off (16–19%) or hid (18–20%). Substantial walking off but no flights occurred at air temperatures below 20 °C, whereas at temperatures of 20 °C or greater, propensity for flight was usually significantly greater than that for walking off.Flights were predominantly toward the tree canopy or inter-tree space, with only a small proportion (17% or less) toward the tree trunk or (in a parallel study) toward an unbaited black pyramid trap (mimicking a tree trunk). Walking was overwhelmingly toward the tree trunk or a black pyramid trap adjacent to the trunk. Our observations lead us to conclude that unbaited black pyramid traps next to trunks of host trees (the most attractive position) can be effective at air temperatures below 20 °C by attracting plum curculio adults that would have entered host trees by walking toward and up tree trunks.Such traps appear to be less effective at 20 °C or greater because under such conditions, adults tend to enter host trees by flight into the canopy.     

What can a weevil teach a fly,and reciprocally? Interaction of host immune systems with endosymbionts in Glossina and Sitophilus

The tsetse fly (Glossina genus) is the main vector of African trypanosomes, which are protozoan parasites that cause human and animal African trypanosomiases in Sub-Saharan Africa. In the frame of the IAEA/FAO program ‘Enhancing Vector Refractoriness to Trypanosome Infection’, in addition to the tsetse, the cereal weevil Sitophilus has been introduced as a comparative system with regards to immune interactions with endosymbionts. The cereal weevil is an agricultural pest that destroys a significant proportion of cereal stocks worldwide. Tsetse flies are associated with three symbiotic bacteria, the multifunctional obligate Wigglesworthia glossinidia, the facultative commensal Sodalis glossinidius and the parasitic Wolbachia. Cereal weevils house an obligatory nutritional symbiosis with the bacterium Sodalis pierantonius, and occasionally Wolbachia. Studying insect host-symbiont interactions is highly relevant both for understanding the evolution of symbiosis and for envisioning novel pest control strategies. In both insects, the long co-evolution between host and endosymbiont has led to a stringent integration of the host-bacteria partnership. These associations were facilitated by the development of specialized host traits, including symbiont-housing cells called bacteriocytes and specific immune features that enable both tolerance and control of the bacteria. In this review, we compare the tsetse and weevil model systems and compile the latest research findings regarding their biological and ecological similarities, how the immune system controls endosymbiont load and location, and how host-symbiont interactions impact developmental features including cuticle synthesis and immune system maturation. We focus mainly on the interactions between the obligate symbionts and their host’s immune systems, a central theme in both model systems. Finally, we highlight how parallel studies on cereal weevils and tsetse flies led to mutual discoveries and stimulated research on each model, creating a pivotal example of scientific improvement through comparison between relatively distant models.

     

Size of orchard trees as a factor affecting behavioural control of apple maggot flies (Dipt., Tephritidae) by traps

Over a 3-year period (1997–1999), we examined the influence of tree size on effectiveness of traps for behaviourally controlling apple maggot flies, Rhagoletis pomonella (Walsh), in small blocks of trees in Massachusetts commercial apple orchards. Traps were red spheres coated with Tangletrap and baited with an attractive synthetic host fruit odour (butyl hexanoate). Traps were placed 6 m apart on perimeter apple trees of each block and were designed to intercept apple maggot flies immigrating into blocks from unmanaged host trees. Based on captures of adults by unbaited red spheres placed near the centre of each block to monitor degree of adult penetration into the interior and on percentages of fruit injured by apple maggot, traps surrounding blocks of small trees (1.5 m canopy diameter) planted at high density were more effective in controlling apple maggot flies (relative to control obtained by insecticide sprays used in comparison blocks) than were traps surrounding blocks of large trees (3.7 m canopy diameter) planted at low density, with traps surrounding blocks of medium-size trees (2.5 m canopy diameter) planted at medium density generally providing an intermediate level of control.     

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.     

BCWEEVIL: A simulation model of the joint population dynamics between spruce weevil and Sitka spruce,over the lifetime of a plantation

The spruce terminal weevil Pissodes strobi (Peck) is a major pest in western spruces, attacking trees of all ages beyond the juvenile stage, killing the leader and causing tree distortion. This paper describes a computer simulation model of the joint population dynamics within this tree/pest system, over the lifetime of a plantation, and is combined with the Province of British Columbia's Tree and Stand Simulator (TASS) to drive individual tree growth and stand establishment and development. The model differs from current models of this system, and of other similar systems, in two important ways: (1) it simulates the entire life of a stand, from planting until harvest, and (2) it is based on the underlying biological processes that govern behavior of individual weevils on and in each tree.Each model simulation begins by planting a stand using tree materials from seed or clonal hedge orchards, choosing trees either individually and independently or in groups represented as clones or families. Stand growth and mortality are advanced through a juvenile period, after which weevils appear in the stand. From this time until harvest, the model simulates daily changes in the weevil populations on each tree, tracking mortality, oviposition, and juvenile maturation and emergence, as well as weevil movement from tree to tree. Once a year, the code projects tree mortality and growth, taking into account within-stand competition and damage to leaders caused by weevil attacks. At harvest, the model computes an estimate of the merchantable timber produced by the stand.As illustrations of model output, we present (1) simulated average numbers of adult and juvenile weevils in stands generated using materials from seed orchards, both throughout a single season and also through the years from stand planting until harvest; and (2) the differential effect of weevil damage on two tree genotypes, one resistant and one susceptible, in a stand composed of adjacent clonal blocks. The results of model simulations are in agreement with some of the population dynamics statistics observed in plantations, suggesting that the model reflects biological realism and can be used as a research or management tool.     

Distribution of the black pecan aphid,Melanocallis caryaefoliae,on the upper and lower surface of pecan foliage

Three aphid species regularly feed on pecan [Carya illinoinensis (Wangenh.) K. Koch (Juglandaceae)] foliage: the black pecan aphid, Melanocallis caryaefoliae (Davis), the yellow pecan aphid, Monelliopsis pecanis Bissell, and the blackmargined aphid, Monellia caryella (Fitch) (all Hemiptera: Aphididae). Adults of M. caryaefoliae and both the nymphs and adults of M. pecanis and M. caryella mainly feed on the lower surface of leaves. Nymphs of M. caryaefoliae appear unique by frequently feeding on the upper surface of pecan leaves. This is risky behavior given the environmental hazards (e.g., rain, solar radiation, and dislodgement) associated with the upper surface. Thus, we determined the leaf surface distribution of M. caryaefoliae on trees in an orchard and on pecan seedlings in the laboratory. A pecan orchard survey found all three aphid species and stages predominantly on the lower leaf surface, except for the nymphs of M. caryaefoliae, which were evenly distributed between upper and lower leaf surfaces. This survey also found aphidophagous lacewing (Neuroptera) larvae predominantly on the lower leaf surface, whereas ladybird beetle (Coleoptera: Coccinellidae) larvae were more evenly distributed between upper and lower surfaces. Laboratory experiments using single or multiple pecan aphid species revealed M. caryaefoliae distribution on pecan seedlings similar to orchard data. Nymphal M. caryaefoliae require nearly 2 days to elicit chlorotic feeding lesions on leaves; without these lesions, nymphal development is hindered. The similar distribution of nymphs of M. caryaefoliae on both leaf surfaces likely reflects a strategy of predator avoidance allowing a proportion of the population to survive.     

A model for long-distance dispersal of boll weevils (Coleoptera: Curculionidae)

The boll weevil, Anthonomus grandis (Boheman), has been a major insect pest of cotton production in the US, accounting for yield losses and control costs on the order of several billion US dollars since the introduction of the pest in 1892. Boll weevil eradication programs have eliminated reproducing populations in nearly 94%, and progressed toward eradication within the remaining 6%, of cotton production areas. However, the ability of weevils to disperse and reinfest eradicated zones threatens to undermine the previous investment toward eradication of this pest. In this study, the HYSPLIT atmospheric dispersion model was used to simulate daily wind-aided dispersal of weevils from the Lower Rio Grande Valley (LRGV) of southern Texas and northeastern Mexico. Simulated weevil dispersal was compared with weekly capture of weevils in pheromone traps along highway trap lines between the LRGV and the South Texas / Winter Garden zone of the Texas Boll Weevil Eradication Program. A logistic regression model was fit to the probability of capturing at least one weevil in individual pheromone traps relative to specific values of simulated weevil dispersal, which resulted in 60.4% concordance, 21.3% discordance, and 18.3% ties in estimating captures and non-captures. During the first full year of active eradication with widespread insecticide applications in 2006, the dispersal model accurately estimated 71.8%, erroneously estimated 12.5%, and tied 15.7% of capture and non-capture events. Model simulations provide a temporal risk assessment over large areas of weevil reinfestation resulting from dispersal by prevailing winds. Eradication program managers can use the model risk assessment information to effectively schedule and target enhanced trapping, crop scouting, and insecticide applications.     

Biology of Centistes delusorius, a parasitoid of adult apple blossom weevil

Abstract

• 1 Natural control of apple blossom weevil, Anthonomus pomorum (L.), deserves attention, as the pest is regaining importance with the declining use of non‐selective pesticides in apple and pear orchards. In this study the biology of Centistes delusorius (Förster), a specific parasitoid of adult apple blossom weevil, is investigated.
• 2 The parasitoid hibernates as young larva in an adult weevil, and juvenile development is resumed in early spring. The fully grown parasitoid larvae leave their hosts during full bloom at the end of April and early May, to pupate. The adults emerging in May oviposit into the newly emerged weevils, which initially feed on apple leaves.
• 3 Centistes delusorius was detected in six out of 15 host‐weevil infested orchards, but was only common in two with larger apple trees standing in grass. There, parasitism levels of around 30% were usual in hosts taken from treebands in winter.
• 4 The delicate larva is vulnerable, and the thin cocoon provides little protection against either desiccation or drowning on a weedless orchard floor. Observations indicate that successful pupation of C. delusorius demands stable humid conditions and some shelter, such as that found in grass or woodland soils.
• 5 Parasitoid females, provided with honey, lived for a mean of 6.3 ± 2.1 days under outdoor conditions in June. Their life span was similar whether they had access to and oviposited in hosts, or not. The species is pro‐ovigenic, and potential fecundity is about 40 eggs. Oviposition usually takes a few seconds. Parasitized female hosts do not reproduce.
• 6 Up to 95% of the parasitoid eggs laid in May develop into a second generation, the adults of which appear in July, when the host has entered aestivation. Older (British) records of C. delusorius outside orchards suggest that some parasitized hosts, like the healthy ones, leave the orchard prior to aestivo‐hibernation, so that the latter do not escape parasitoid attack in July.
• 7 A trapping sample in late June, when most non‐parasitized weevils have gone into aestivo‐hibernation, is probably the most efficient method to detect parasitized weevils.
• 8 The (near‐)absence of C. delusorius in many orchards is probably due not only to pesticide side‐effects, or scarcity of its host, but also to the absence of suitable pupation sites for the wasp.

     

Differential susceptibility and suitability of domestic and wild apple species for a florivorous weevil and its parasitoids

Crop plant domestication can change plant resistance to herbivores leading to differences in pest pressure experienced by crop plants and their wild relatives. To compare resistance to herbivores between domesticated and wild fruit trees, we quantified direct resistance and indirect resistance to a pest insect, the florivorous apple blossom weevil Anthonomus pomorum (Coleoptera: Curculionidae), for the cultivated apple Malus domestica and two wild apple species, the European crab apple M. sylvestris and the exotic M. kirghisorum. We measured weevil infestation and performance (weight, sex ratio), and weevil parasitism by parasitoid wasps for different cultivars of M. domestica and for the two wild apple species. To explain weevil and parasitoid responses to different apple species, we quantified tree characteristics including nitrogen content, size of flower buds, bark roughness, tree size, tree phenology and tree position. We found significant differences in susceptibility to weevil infestation between apple species, with lowest infestation (highest apple resistance) in M. domestica and highest infestation in M. kirghisorum. The suitability of apple species also varied significantly: weevils emerging from M. sylvestris were significantly lighter than those from M. kirghisorum. Parasitism of A. pomorum by different parasitoid species was significantly higher in M. sylvestris than in M. domestica. Infestation, weevil weight and parasitism were positively related to tree characteristics: infestation to bud nitrogen content and bark roughness, weevil size to nitrogen content and bud size, and parasitism to tree height and bud density. Our study revealed marked differences between apple species in susceptibility and suitability for the pest herbivore, but also for antagonistic parasitoids. Whereas direct resistance appeared to be higher in cultivated apple, indirect resistance via parasitoids was apparently higher in wild apple trees. Our findings suggest that wild and cultivated apple trees possess different resistance traits that may be combined to optimize resistance in commercial apple cultivars.     

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.     

Olfactory and visual stimuli used in orientation to conifer seedlings by the pine weevil, Hylobius abietis

Abstract. The influence of noncontact plant cues is investigated on the likelihood that individual conifer seedlings will be found by walking adults of the pine weevil, Hylobius abietis, in the field. Traps with solely odour or solely visual stimuli catch significantly more weevils than stimulus-free traps, and traps with the combination of odour and visual stimuli catch more weevils than traps with odour or visual stimuli alone. There is essentially an additive effect between odour and visual stimuli. The reactions to odour and visual stimuli are similar for three phases of the pine weevil's life cycle associated with three ages of clear-cuttings (i.e. sites where all trees have been harvested). Visual stimuli appear to be at least as important as odour for the pine weevil in finding an undamaged conifer seedling.     

Spatio‐temporal distribution of Ceratitis capitata population in a heterogeneous landscape in Central Italy

The spatio‐temporal dynamics of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was investigated to evaluate the effect of the landscape elements and host plants on pest distribution, in an agricultural landscape of 500 ha located in Central Italy. Two farms (farm 1 and farm 2) are located in the experimental area, composing mixed fruit orchards and surrounded by hedgerows, small woodlots, private gardens and cereal fields. Ceratitis capitata population fluctuation was monitored, from 2006 to 2008, using traps baited with trimedlure. Geostatistical methods such as Inverse distance squared weighted were used to obtain distributional maps of adults, mainly males. Results showed that the adult Mediterranean fruit flies were primarily distributed inside farm 1, with the maximum density found in the months of September and October. Away from the principal host plants, particularly in cereal fields, the number of trapped individuals was always low or zero. In both farms, flies were caught sequentially in traps located on host plants (i.e. peach, apple, pear, oriental persimmon and prickly pear) at varying times of maturation, especially when fruits remained on the trees. Distributional maps provided evidence that allowed to identify habitats in which the fly developed early in the season (mixed peach orchards) and afterwards during the periodic flights.