Plum Curculio Research Articles

Management of Plum Curculio and Catfacing Insects on Peaches in Central Alabama: Standard Crop Stage–Based vs. Integrated Pest Management–Based Approaches

ABSTRACT Plum curculio, tarnished plant bug, brown stink bug, and green stink bug are the major insect pests causing fruit damage on peaches grown in the southeastern United States. Insect management aids, monitoring techniques, predictive models, and action thresholds for southeastern peaches are either lacking or they are not robust enough to facilitate industry acceptance of as-needed insecticide applications during the growing season (Horton et al., 2003). In this 3-year study, we compared two approaches to scheduling insecticide applications for control of these pests on three peach cultivars in an established central Alabama orchard: 1) an industry standard, representative of prevailing practice in the southeastern United States, which consisted of scheduled insecticide applications timed to coincide with crop stage; and 2) an integrated pest management (IPM) treatment, which employed limited prescheduled insecticide applications timed to coincide with the crop's developmental stage, supplemented with as-needed insecticide applications when preestablished action thresholds were reached. Percentage of insect-damaged fruit from trees under the IPM treatment was similar to, or in some cases greater or less than, that of fruit from trees receiving the standard treatment. Depending on the year, the same or fewer insecticide applications were made under the IPM treatment compared with the standard treatment. The IPM treatment came close to providing acceptable levels of plum curculio control with the early-season cultivar Correll but not with the mid- and late-season cultivars Sunland and Biscoe.

Abiotic Factors and Trap Design Modulate the Performance of Traps Used to Monitor the Plum Curculio

All published studies on effects of abiotic factors on plum curculio, Conotrachelus nenuphar (Hersbt), adults have taken a retrospective approach. Here, we present the results of experiments where factors and their levels were determined and controlled a priori. We compared the effectiveness of miniature pyramidal traps (45 by 20 by 20 cm) constructed of four kind of materials--wood, geotextile, nylon screening, and corrugated plastic--to monitor overwintered and summer adults of univoltine plum curculio. We also studied the effects of photoperiod, temperature, wind, and rain on pyramidal trap effectiveness. The experiments, which were replicated over time, were done in two controlled chambers that were divided into four sections, corresponding to simulated combinations (wind or no wind/rain or no rain). The temperatures tested (15, 20, and 25 degrees C) were randomly assigned in the chambers. During scotophase, geotextile traps captured significantly more overwintered and summer adults than traps made of other materials. The maximum proportion of captures (for overwintered and summer adults) during photophase was obtained at 25 degrees C, and it was significantly different than captures at 15 and 20 degrees C. During scotophase, significantly more overwintered and summer plum curculios were caught at 20 and 25 degrees C than at 15 degrees C. Our experiments demonstrated that geotextile is a good alternative to wooden pyramidal trap. Our results suggest that captures were higher 1) at night, 2) during warmer periods (20 and 25 degrees C), 3) when wind velocity was low and 4) during or shortly after rainfall, and 5) that photoperiod is a factor having an important predictive value for plum curculio captures.

Potential of Two Entomopathogenic Nematodes for Suppression of Plum Curculio (Conotrachelus nenuphar, Coleoptera: Curculionidae) Life Stages in Northern Climates

Plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruits in North America. We evaluated the potential efficacy of two entomopathogenic nematode species for suppression of plum curculio in northern regions, targeting life stages that reside in soil during spring and summer. A strain of Heterorhabditis bacteriophora isolated from soil infested with plum curculio in northern Utah and a commercially available strain of Steinernema feltiae known to tolerate cool temperatures were tested in the laboratory against three life stages of plum curculio. Bioassays used the southern strain of plum curculio because availability of the northern strain from the field was inadequate. H. bacteriophora was more virulent than S. feltiae to all plum curculio life stages. Adults and pupae were more susceptible than larvae. Temperature bioassays were conducted with a surrogate host: last instars of Galleria mellonella. The two nematodes exhibited different, but overlapping, thermal activity ranges. Both species performed best at 20°C: virulence and reproductive potential was higher; however, H. bacteriophora was superior to S. feltiae at 30°C and vice versa at 10°C. The reproductive potential of H. bacteriophora was >2.5 times greater than for S. feltiae, and H. bacteriophora required fewer individuals to initiate a successful host infection. S. feltiae was a better fit for temperatures expected in northern climates, but H. bacteriophora was more virulent to plum curculio and produced more infective juveniles that may benefit nematode recycling and continuation and spread of insect suppression in the field.

Potential of Two Entomopathogenic Nematodes for Suppression of Plum Curculio (<I>Conotrachelus nenuphar</I>, Coleoptera: Curculionidae) Life Stages in Northern Climates

Plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruits in North America. We evaluated the potential efficacy of two entomopathogenic nematode species for suppression of plum curculio in northern regions, targeting life stages that reside in soil during spring and summer. A strain of Heterorhabditis bacteriophora isolated from soil infested with plum curculio in northern Utah and a commercially available strain of Steinernema feltiae known to tolerate cool temperatures were tested in the laboratory against three life stages of plum curculio. Bioassays used the southern strain of plum curculio because availability of the northern strain from the field was inadequate. H. bacteriophora was more virulent than S. feltiae to all plum curculio life stages. Adults and pupae were more susceptible than larvae. Temperature bioassays were conducted with a surrogate host: last instars of Galleria mellonella. The two nematodes exhibited different, but overlapping, thermal activity ranges. Both species performed best at 20 degrees C: virulence and reproductive potential was higher; however, H. bacteriophora was superior to S. feltiae at 30 degrees C and vice versa at 10 degrees C. The reproductive potential of H. bacteriophora was > 2.5 times greater than for S. feltiae, and H. bacteriophora required fewer individuals to initiate a successful host infection. S. feltiae was a better fit for temperatures expected in northern climates, but H. bacteriophora was more virulent to plum curculio and produced more infective juveniles that may benefit nematode recycling and continuation and spread of insect suppression in the field.

Evaluation of Reproductive Compatibility of Interstrain Matings Among Plum Curculio Populations in the Eastern United States

Reproductive compatibility of interstrain matings in plum curculio, Conotrachelus nenuphar (Herbst), was studied during the summers of 2004 and 2006. There was a unidirectional incompatibility in the cross-matings along a rough north to south transect of the range of plum curculio (4 × 4 two-factorial design). There was significantly lower fertility in West Virginia males mated with New York and Virginia females (40 and 29%, respectively), and Florida males had a significantly lower fertility with Virginia and West Virginia females (46 and 37%, respectively), but Florida females were compatible with males of all four populations. Three northern populations were compatible with each other in all cross-mating combinations (New York, Massachusetts, and New Jersey; 3 × 3 two-factorial design). There was a unidirectional reproductive incompatibility in the combination of New Jersey males with Florida females (47%) and a bi-directional incompatibility between Florida and West Virginia reciprocal cross-mating (26 and 21%, respectively). The pattern of the reproductive incompatibility among geographic populations could help us to distinguish plum curculio strains and to clarify their strain distribution range to enrich our knowledge on their population ecology and biosystematics.

Evaluation of Reproductive Compatibility of Interstrain Matings Among Plum Curculio Populations in the Eastern United States

Reproductive compatibility of interstrain matings in plum curculio, Conotrachelus nenuphar (Herbst), was studied during the summers of 2004 and 2006. There was a unidirectional incompatibility in the cross-matings along a rough north to south transect of the range of plum curculio (4 x 4 two-factorial design). There was significantly lower fertility in West Virginia males mated with New York and Virginia females (40 and 29%, respectively), and Florida males had a significantly lower fertility with Virginia and West Virginia females (46 and 37%, respectively), but Florida females were compatible with males of all four populations. Three northern populations were compatible with each other in all cross-mating combinations (New York, Massachusetts, and New Jersey; 3 x 3 two-factorial design). There was a unidirectional reproductive incompatibility in the combination of New Jersey males with Florida females (47%) and a bi-directional incompatibility between Florida and West Virginia reciprocal cross-mating (26 and 21%, respectively). The pattern of the reproductive incompatibility among geographic populations could help us to distinguish plum curculio strains and to clarify their strain distribution range to enrich our knowledge on their population ecology and biosystematics.

Genetic Diversity of Plum Curculio (Coleoptera: Curculionidae) Among Geographical Populations in the Eastern United States

This study investigated the genetic diversity among plum curculio, Conotrachelus nenuphar (Herbst), populations from 11 different geographic locations by using partial sequences of mitochondrial cytochrome oxidase I (mtCOI) gene. Polymerase chain reaction (PCR) products were 863 bp. In total, 23 unique haplotypes were identified from 50 tested samples. Haplotypes G (n = 5), L (n = 12), and T (n = 13) made up 60% of the 50 samples. Two distinct major clades were found in the phylogenetic analyses. Northern and southern clades were strongly supported (100/83 (MP/ML) and 100/62, respectively) by bootstraps. The mid-southern subclade within the southern clade was also moderately supported by bootstraps (73/57, MP/ML). The results of analyses of molecular variance (AMOVA) are consistent with phylogenetic analysis. The results suggested that the northern and the southern clades correspond with northern strain and southern strain of plum curculio. The three-group model of AMOVA test may suggest that there is a transitional group existing between northern and southern groups. In this study, the mtCOI sequence was highly informative as a molecular marker in that it could distinguish C. nenuphar from northern and southern geographic locations in the eastern United States.

Odor-Baited Trap Trees: A Novel Management Tool for Plum Curculio (Coleoptera: Curculionidae)

The plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), one of the most important pests of apple (Malus spp.) in eastern and central North America, historically has been managed in New England apple orchards by three full block insecticide applications. Efforts to reduce insecticide inputs against plum curculio include perimeter row sprays, particularly after petal fall, to control immigrating adults. The odor-baited trap tree approach represents a new reduced input strategy for managing plum curculio based on the application of insecticides to a few perimeter-row trap trees rather than the entire perimeter row or full orchard block. Here, we compared the efficacy of a trap tree approach with perimeter row treatments to manage populations after petal fall in commercial apple orchards in 2005 and 2006. Injury was significantly greater in trap trees compared with unbaited perimeter row treated trees in both years of the study. In 2005, heavy rains prevented growers from applying insecticide applications at regular intervals resulting in high injury in nearly all blocks regardless of type of management strategy. In 2006, both the trap-tree and perimeter-row treatments prevented penetration by immigrating populations and resulted in economically acceptable levels of injury. The trap tree management strategy resulted in a reduction of approximately 70% total trees being treated with insecticide compared with perimeter row sprays and 93% compared with standard full block sprays.

Reproductive Development of Female Plum Curculio (Coleoptera: Curculionidae) in the Mid-Atlantic: Presence of Multivoltine Populations

The plum curculio, Conotrachelus nenuphar (Herbst), is a key pest of pome and stone fruit throughout eastern and central North America. There are two strains of plum curculio, the univoltine ‘northern’ strain and the multivoltine ‘southern’ strain. Voltinism associated with populations located in the mid-Atlantic region has been unclear from historic records, with recent studies suggesting multivoltine populations. In studies conducted in West Virginia, female plum curculios obtained from emergence and screen traps and from samples of host tree canopies strongly indicate the presence of at least some multivoltine populations, based on an ovarian development bioassay. Two periods of active oogenesis were detected. The first occurred in early spring between late April and early May and represented overwintered females reaching sexual maturity. A second period of oogenesis was detected beginning in late June and continuing through early August. Based on degree day accumulations and known developmental rates of plum curculio, the mid-Atlantic is comprised, at least in part, of multivoltine populations. Fruit growers, therefore, must consider that plum curculio can pose a threat to tree fruit throughout the active growing season.

Ovicidal Activity of Organophosphate, Oxadiazine, Neonicotinoid and Insect Growth Regulator Chemistries on Northern Strain Plum Curculio,Conotrachelus nenuphar

An in vitro method was developed for assessing ovicidal effects of the organophosphate azinphos-methyl, the neonicotioids thiacloprid, thiamethoxam and clothianidin, the oxadiazine indoxacarb and the insect growth regulators novaluron and pyriproxifen on the plum curculio, Conotrachelus nenuphar (Herbst)(Coleoptera: Curculionidae). The baseline survivorship of this method was 88 percent. Plum curculio eggs were most sensitive to azinphos-methyl. Thiacloprid, clothianidin and the chitin synthesis inhibitor, novaluron, had LC50 values below 100 ppm. Thiamethoxam, indoxacarb and pyriproxifen were not ovicidal at 100 ppm. Octanol-water partitioning coefficients, log Kow, appeared to be an important indicator of ovicidal activity within the neonicotinoids. This new bioassay method eliminates the confounding of the insect-chemical and plant-chemical interactions and the results highlight the utility of a post-infestation curative approach to plum curculio management.

Predicting insect distributions from climate and habitat data

Knowing the effects of climate and habitat on the distributions of insect pests and their natural enemy would help target the search for natural enemies, increase establishment of intentional introductions, improve risk assessment for accidental introductions and the effects of climate change. Most existing methods used to predict geographical distributions of insects either involve subjective comparisons of climate or require data concerning insect responses to climate. Here we have used geographical distributions of insects to develop statistical models for the effects of climate and habitat on these distributions. We tested this approach using six insect pests found in the United States: Ostrinia nubilalis (European corn borer), Diuraphis noxia (Russian wheat aphid), Helicoverpa zea (Corn earworm), Leptinotarsa decemlineata (Colorado potato beetle), Solenopsis invicta (Red imported fire ant), and Conotrachelus nenuphar (Plum curculio). By randomly separating the data into model-building and test sets, we were able to estimate prediction accuracy. For each species, a unique combination of predictor variables was identified. The models correctly predicted presence for more than 92% of the data on each insect species. The models correctly predicted absence for 59% to 77% of the data on five of six species. Absence predictions were poor for H. zea (21% correct), because distribution data were limited and inaccurate. Predictions of insect absence were more difficult because absence data were less abundant and perhaps less reliable. This approach offers potential for the analysis of existing data to produce predictions about insect establishment. However, accurate prediction depends heavily on data quality, and in particular, more data are needed from locations where insects are sampled but not found.

Susceptibility of Fruit from Diverse Apple and Crabapple Germplasm to Attack by Plum Curculio (Coleoptera: Curculionidae)

Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important apple, Malus domestica Borkh., pest that significantly hinders sustainable apple production in eastern North America. The potential for host plant resistance to plum curculio among apple germplasm has never been rigorously evaluated. Thus, studies were conducted to assess the susceptibility of a number of exotic and domestic Malus accessions housed at the USDA Plant Genetic Resources Unit (PGRU) "core" collection in Geneva, NY. Contrary to earlier published reports and promising data from a field assessment in 2005, these results suggest that there is probably little potential for genetic resistance to plum curculio among the Malus germplasm collection evaluated. More specifically, four Malus hybrid selections that have previously been released with claims of plum curculio resistance were shown to be susceptible to plum curculio attack. Because there are additional accessions housed at PGRU outside of the core collection that are currently classified as resistant, further studies are necessary to evaluate the true resistance qualities of these releases. It is also important to clarify such discrepancies in both the USDA online Germplasm Resources Information Network and in the horticultural literature. Although other Malus species exhibited some variability in fruit susceptibility, none could be classified as being truly resistant to plum curculio attack by any definition that would have relevance to commercial production and sale of apples.

Susceptibility of Fruit from Diverse Apple and Crabapple Germplasm to Attack by Plum Curculio (Coleoptera: Curculionidae)

Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important apple, Malus domestica Borkh., pest that significantly hinders sustainable apple production in eastern North America. The potential for host plant resistance to plum curculio among apple germplasm has never been rigorously evaluated. Thus, studies were conducted to assess the susceptibility of a number of exotic and domestic Malus accessions housed at the USDA Plant Genetic Resources Unit (PGRU) “core” collection in Geneva, NY. Contrary to earlier published reports and promising data from a field assessment in 2005, these results suggest that there is probably little potential for genetic resistance to plum curculio among the Malus germplasm collection evaluated. More specifically, four Malus hybrid selections that have previously been released with claims of plum curculio resistance were shown to be susceptible to plum curculio attack. Because there are additional accessions housed at PGRU outside of the core collection that are currently classified as resistant, further studies are necessary to evaluate the true resistance qualities of these releases. It is also important to clarify such discrepancies in both the USDA online Germplasm Resources Information Network and in the horticultural literature. Although other Malus species exhibited some variability in fruit susceptibility, none could be classified as being truly resistant to plum curculio attack by any definition that would have relevance to commercial production and sale of apples.

Control of plum curculio, Conotrachelus nenuphar, with entomopathogenic nematodes: Effects of application timing, alternate host plant, and nematode strain

In prior research, we established that soil applications of Steinernema riobrave in peach orchards that target plum curculio, Conotrachelus nenuphar, larvae can result in high levels of control (78–100%). In this study, we investigated the potential of using entomopathogenic nematodes to control C. nenuphar further by evaluating (1) field efficacy of late-term nematode applications, i.e., that target C. nenuphar after the onset of adult emergence, (2) control C. nenuphar larvae in an alternate host, i.e., wild plum, Prunus angustifolia, and (3) laboratory virulence of different Steinernema carpocapsae and S. riobrave strains. In 2004 and 2005, late-term applications of S. carpocapsae (All strain) and S. riobrave (355 strain) in a peach orchard in Quincy, Florida failed to cause any measurable control. In field tests targeting C. nenuphar larvae in a wild plum thicket (Byron, Georgia), S. riobrave (355 strain) caused 100% control (both years), and S. riobrave (3-8b strain) caused 98.6% and 87.9% control in 2005 and 2006, respectively. Applications in alternate hosts could reduce C. nenuphar immigration into the orchard. Laboratory experiments detected differential virulence to C. nenuphar larvae in S. carpocapsae (All strain) and six strains of S. riobrave; among the most virulent were the 3-2, 3-3, and 355 strains of S. riobrave. Pathogenicity to adult C. nenuphar in the laboratory was not detected in five S. riobrave strains, but was detected in four S. carpocapsae strains (All, Agriotos, Italian and Sal) but not in two others (Kapow and Mexican). We conclude that soil applications with entomopathogenic nematodes can cause high levels of C. nenuphar control in peach or alternate hosts, but timing of application and the choice of nematode species or strain can be important.

Pyriproxyfen activates reproduction in prediapause northern strain plum curculio (Conotrachelus nenuphar Herbst)

Field-collected, prediapause northern strain plum curculio, Conotrachelus nenuphar (Herbst), adults were treated with the juvenile hormone analogue pyriproxyfen to assess effects on reproductive development. Adults of this pest have an obligate winter reproductive diapause and do not reach reproductive maturity until after spring emergence. Topical (1.0 microL) doses of 10, 1.0 and 0.1 microg microL(-1) pyriproxyfen induced oocyte development and reproductive maturation in all treated females as assessed by dissection. There was no increased mortality in treated beetles, and control insects showed no reproductive maturation. Treatment of prediapause males and females with 1.0 microg microL(-1) of topical pyriproxyfen or exposure to residues on fruit induced successful egg laying and F1 emergence; F1 pupation success in topical treatments and residue exposure was 47 and 59% respectively. Filial adults require re-exposure to initiate reproductive development. Treatment protocols with pyriproxyfen will allow researchers to culture the northern strain, instead of relying exclusively on the non-diapausing southern strain.

Novel life stage targets against plum curculio, Conotrachelus nenuphar (Herbst), in apple integrated pest management

In this study the authors employed the plant-insect-chemistry (PIC) triad to investigate two novel life stage targets against the plum curculio (PC), Conotrachelus nenuphar (Herbst), in apple integrated pest management (IPM). Laboratory treated apple bioassays were used to determine if the insect growth regulator (IGR) insecticides novaluron and tebufenozide have physiological effects on PC larvae following adult exposure. Curative activity bioassays were conducted for IGR, neonicotinoid, oxidiazine and organophosphate insecticides on PC larvae post-infestation, and fruit penetration profiles of insecticides were developed. The results revealed that novaluron exhibits activity on PC larvae via vertical transmission following exposure of mated females to treated substrate. Surface treatments of azinphos-methyl, thiacloprid and thiamethoxam to preinfested fruit resulted in significant reductions in larval emergence. For all compounds, 50% or more of the total recovered active ingredient was from apple skin, and for azinphos-methyl, indoxacarb and thiamethoxam it was greater than 80%. For azinphos-methyl, novaluron, methoxyfenozide and thiacloprid, however, active ingredient was recovered from every section of the apple, from skin to core. Implications for twenty-first century IPM are discussed.

Impact of Trap Architecture, Adjacent Habitats, Abiotic Factors, and Host Plant Phenology on Captures of Plum Curculio (Coleoptera: Curculionidae) Adults

Pyramid traps, 2.44 m and 3.66 m in height, were compared with standard-sized pyramid traps, 1.22 m in height, to assess the impact of trap architecture on captures of adult plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), in two apple (Malus spp.) orchards and a blueberry (Vaccinium spp.) planting. The effects of adjacent habitat (organic orchard versus wooded areas), abiotic factors, and phenological stages of apple also were assessed to determine whether these variables influenced trap captures. Standard-sized pyramidal traps captured significantly more adults than larger trap variants. In the apple orchards, most adults (70-80%) were captured before petal fall with the exception of blocks adjacent to the organic orchard (25%). Significantly more adults were captured along the edge of an apple orchard (managed using an integrated pest management strategy) facing an organic apple orchard (76%) than along the edge facing wooded areas (24%). There was a significant positive correlation between daily trap captures and mean daily temperatures before petal fall in apple orchards.

Impact of Temperature on Plum Curculio (Coleoptera: Curculionidae) Responses to Odor-Baited Traps

In 2005, captures of overwintered adult plum curculios, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), in standard black masonite pyramid traps deployed in apple (Malus spp.) orchards from half-inch green until fruit reached 7 mm and baited with known attractants did not result in significant captures compared with unbaited traps as they had in 2003 and 2004. These baits included the synthetic aggregation pheromone, grandisoic acid (GA) alone, a six-component synthetic host plant volatile combination (6-Tree) identified from foliar and woody tissues of a Stanley plum tree in combination with GA (6-Tree+GA), and the synthetic fruit volatile benzaldehyde (BEN) in combination with GA (BEN+GA). In 2005, the average daily temperature was below 13 degrees C, much cooler than in 2003 and 2004. We hypothesized that plum curculio could not discriminate between baited and unbaited traps because of reduced release rates of odor-bait stimuli due to their temperature-driven release system. From data collected from 2003 to 2005, we found that plum curculio captures in traps baited with GA alone, 6-Tree+GA, and BEN+GA were significantly related to temperature. We created a predictive model to determine the level of activity, i.e., trap captures in baited traps compared with unbaited traps, we would expect to observe at a particular temperature for these same odor stimuli. Our models predicts that at temperatures between approximately 11 to 13 degrees C we would expect to see no difference between captures in baited and unbaited traps. For captures in odor-baited traps to reach twice those in unbaited traps, our model predicts that temperatures must reach 19.2 degrees C for GA alone, 18.5 degrees C for 6-Tree+GA, and 15.8 degrees C for BEN+GA.

Impact of Temperature on Plum Curculio (Coleoptera: Curculionidae) Responses to Odor-Baited Traps

In 2005, captures of overwintered adult plum curculios, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), in standard black masonite pyramid traps deployed in apple (Malus spp.) orchards from half-inch green until fruit reached 7 mm and baited with known attractants did not result in significant captures compared with unbaited traps as they had in 2003 and 2004. These baits included the synthetic aggregation pheromone, grandisoic acid (GA) alone, a six-component synthetic host plant volatile combination (6-Tree) identified from foliar and woody tissues of a Stanley plum tree in combination with GA (6-Tree+GA), and the synthetic fruit volatile benzaldehyde (BEN) in combination with GA (BEN+GA). In 2005, the average daily temperature was below 13°C, much cooler than in 2003 and 2004. We hypothesized that plum curculio could not discriminate between baited and unbaited traps because of reduced release rates of odor-bait stimuli due to their temperature-driven release system. From data collected from 2003 to 2005, we found that plum curculio captures in traps baited with GA alone, 6-Tree+GA, and BEN+GA were significantly related to temperature. We created a predictive model to determine the level of activity, i.e., trap captures in baited traps compared with unbaited traps, we would expect to observe at a particular temperature for these same odor stimuli. Our models predicts that at temperatures between ≈ 11 to 13°C we would expect to see no difference between captures in baited and unbaited traps. For captures in odor-baited traps to reach twice those in unbaited traps, our model predicts that temperatures must reach 19.2°C for GA alone, 18.5°C for 6-Tree+GA, and 15.8°C for BEN+GA.

Moisture Effects on Development and Survival of the Plum Curculio (Coleoptera: Curculionidae)

Laboratory-reared larvae of Conotrachelus nenuphar Herbst were exposed to three soil moisture treatments in pots containing a mix of soil and vermiculite, whereby pots were either watered daily (wet treatment) or watered to saturation when matric potential reached threshold values of −160 and −800 kPa for the intermediate and dry treatments, respectively. Adult emergence began at approximately the same time in the 3 treatments, but peak emergence (occurring ~1 month after the start of the experiment and within 2 wks of the beginning of emergence) was much more pronounced in the intermediate moisture treatment than in the wet and dry ones. In addition, cumulative emergence in the intermediate moisture treatment (corresponding to >40% of the initial number of larvae used in the experiment) was higher than in the wet (~30%) and dry (~20%) treatments. Approx. 25% of the adults that emerged from the dry treatment were underdeveloped and/or malformed. In a separate set of experiments, the effect of air humidity on survival of laboratory-reared plum curculio adults was investigated. Survival analysis revealed a significant (P< 0.0001) effect of vapor pressure deficit on adult longevity. As vapor pressure deficit decreased from ~2.8 to 0.009 kPa, median life expectancy increased from 1.1 to 9.0 d for insects without food supply and from 7.0 to 30.5 d for insects feeding on apples. Longevity correlated with cumulative water loss from the insects, which was lowest in a saturated atmosphere and greatest for insects exposed to a vapor pressure deficit of ~2.8 kPa. Cuticular permeability of C. nenuphar to water was calculated as 185.8 μg cm−2 kPa−1.