Response of Adult Plum Curculios (Coleoptera: Curculionidae) to Contrasting Shades in Field and Laboratory Experiments

The responses of adult plum curculios, Conotrachelus nenuphar (Herbst), to visual stimuli were assessed in field and laboratory conditions to evaluate the hypothesis that adult captures should increase when traps visually contrast with a lighter horizon, such as the sky. Release-recapture field studies tested whether adult responses to traps were influenced by the trap's visual contrast with background on the horizon. Results at four sites showed that significantly more adults were captured in traps with woodlots behind them, refuting the hypothesis. Laboratory tests in environmental conditions of 315 lux or less observed the movement of adults between intervals. These showed that significantly more females and males relocated in areas marked with black. This effect occurred when adults were presented with black surfaces, stripes, or lines. The black shade used correlated with lower reflected lux (<110), and when in conditions of ≤ 10 lux, significant adult relocation on black was not observed. These results suggest that adults arrest in or move toward areas with low reflected lux. The laboratory and field results combined suggest that higher adult captures in traps correlated with the largest areas of low lux on the horizon. The results imply that trap placement should take reflected lux from all nearby objects into account and that even in small patterns on traps, variance in shade or reflected lux may permit manipulation of plum curculio movement.

Comparing the emergence of northern strain plum Curculio larvae from multiple fruit varieties

Increasing restrictions on chemical pesticide use in orchards have encouraged the use of alternative strategies to control the northern strain of the plum curculio, Conotrachelus nenuphar (Herbst). Some of these strategies target larvae as they emerge from fruit, so existing models for larval emergence from fruit were evaluated for accuracy while examining the effect of multiple larvae and fruit type on emergence timing. Larval head width growth rate was established and used to gauge larval development. Larval emergence timing, quantified as degree-days (base 11.1 degrees C), was recorded in tart cherries on trees, and emergence timing was recorded in multiple apple varieties both in cyclical field conditions and in constant laboratory conditions. Ovipositing females and fruit were isolated, so larvae in a fruit were all siblings. Adult emergences from pupation in soil were recorded in the laboratory and compared with existing model predictions. Model predictions did not accurately reflect the timing of larval or adult emergence, and future incorporation of factors that could improve models are discussed. Colder conditions and changing host fruit type had no significant effect on larval emergence timing but changing host fruit type correlated with a shorter pupation interval. Results suggested that females preferred to oviposit on multiple fruit rather than lay multiple eggs in one fruit. Higher numbers of larvae per fruit did not significantly alter the timing of first larval emergence, although more larvae per fruit resulted in a significantly longer emergence period in apples.

Precise and low-cost monitoring of plum curculio (Coleoptera: Curculionidae) pest activity in pyramid traps with cameras

Incorporating camera systems into insect traps potentially benefits insect phenology modeling, nonlethal insect monitoring, and research into the automated identification of traps counts. Cameras originally for monitoring mammals were instead adapted to monitor the entrance to pyramid traps designed to capture the plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae). Using released curculios, two new trap designs (v.I and v.II) were field-tested alongside conventional pyramid traps at one site in autumn 2010 and at four sites in autumn 2012. The traps were evaluated on the basis of battery power, ease-of-maintenance, adaptability, required-user-skills, cost (including labor), and accuracy-of-results. The v.II design fully surpassed expectations, except that some trapped curculios were not photographed. In 2012, 13 of the 24 traps recorded every curculio entering the traps during the 18-d study period, and in traps where some curculios were not photographed, over 90% of the omissions could be explained by component failure or external interference with the motion sensor. Significantly more curculios entered the camera traps between 1800 and 0000 hours. When compared with conventional pyramid traps, the v.I traps collected a similar number of curculios. Two observed but not significant trends were that the v.I traps collected twice as many plum curculios as the v.II traps, while at the same time the v.II traps collected more than twice as many photos per plum curculio as the v.I traps. The research demonstrates that low-cost, precise monitoring of field insect populations is feasible without requiring extensive technical expertise.

Behavioral and electroantennogram responses of plum curculio, Conotrachelus nenuphar, to selected noxious plant extracts and insecticides

Behavioral and electroantennogram responses of plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), adults were tested for several methanolic plant extracts and organically approved insecticides. Plant extracts were evaluated for their potential as antifeedants or oviposition deterrents. These extract responses were also compared to those elicited by the non-neurotoxic, organic irritant-insecticide kaolin clay. Both sexes of plum curculio exhibited antennal response as measured by electroantennogram, which ranged from 0.2 to 1.1 mV, to plant extracts and the organic irritant/insecticide, with the greatest response to the extract of rough cocklebur, Xanthium strumarium L. (1.1 mV). No choice tests were conducted to compare feeding and oviposition by plum curculio on untreated apples or on apples treated with one of the extracts or the insecticide. The insecticide pyrethrum and extracts of X. strumarium and greater burdock, Arctium lappa L., significantly reduced feeding. Also, pyrethrum, A. lappa, Humulus lupulus L. (common hop), X. strumarium, and Verbascum songaricum Schrenk extracts completely inhibited egg deposition. In no-choice assays, the effects of kaolin clay with incorporated plant extracts on plum curculio feeding and oviposition were monitored as complementary tests. A. lappa-kaolin, H. lupulus-kaolin, and X. strumarium-kaolin mixtures significantly reduced the feeding of plum curculio compared to the control or kaolin clay alone. Each of the plant extract-kaolin mixtures evaluated, with the exception of Bifora radians Bieberstein (wild bishop), completely inhibited plum curculio oviposition as compared to controls.

Field efficacy of entomopathogenic fungi and nematodes targeting caged last-instar plum curculio (Coleoptera: Curculionidae) in Michigan cherry and apple orchards

The plum curculio (Conotrachelus nenuphar Herbst) is a key pest of pome and stone fruit in eastern North America. We tested the efficacy of five pathogens over the course of three seasons in 10 Michigan apple and cherry orchards, with introductions of larvae to caged pots containing pathogen-treated soil. The nematode Steinernema riobrave was the most effective pathogen in the 2 yr it was tested, but only in soils with the highest sand content (81-88%) and when it was applied 1 h or 5 d after last instars of plum curculio. S. carpocapsae in an organic formulation was less effective, but significantly reduced plum curculio emergence in 1 yr of the study when applied 3 d before C. nenuphar larvae were introduced. Beauveria bassiana was effective in only 1 of the 3 yr it was tested, only in soils with lower sand content, and only when it was introduced within 1 h of plum curculio larvae. Metarhizium anisopliae and Heterorhabditis bacteriophora were ineffective. Michigan orchards may require sprinkler irrigation coupled with precise timing recommendations and oviposition monitoring to enhance entomopathogen application efficacy against soil-dwelling last instars.

Inheritance of resistance to Bacillus thuringiensis subsp. tenebrionis CryIIIA delta-endotoxin in Colorado potato beetle (Coleoptera: Chrysomelidae)

We investigated the genetic inheritance of Colorado potato beetle, Leptinotarsa decemlineata (Say), resistance to Bacillus thuringiensis CryIIIA delta-endotoxin. Standard reciprocal crosses and backcrosses between susceptible (S) and resistant (R) strains were used to determine the characteristics of resistance. Analysis of probit lines from the F1 reciprocal crosses indicated that B. thuringiensis delta-endotoxin resistance was inherited autosomaly without maternal effects. We estimated the degree of dominance to be 0.77 and 0.76 for the (R x S) and (S x R) F1 generations, respectively, indicating that B. thuringiensis CryIIIA delta-endotoxin resistance is conferred by incompletely dominant genes. Chi-square analysis of mortality responses of backcrossed offspring suggested that resistance might be caused by more than one locus. The stability of resistance was also studied by testing seventeen generations of resistant beetles after the selection pressure was removed. When the selection pressure was removed, the resistance level of the selected colony decreased after five generations. The resistance level did not decrease further when the selection was removed for > 12 generations.

Managing Insect Resistance to Bacillus thuringiensis Toxins

Bacillus thuringiensis (B.t.) delta-endotoxins provide an alternative to chemical insecticides for controlling many species of pest insects. Recent biotechnological developments offer the promise of even greater use of B.t. toxins in genetically transformed pest-resistant crops. However, the discovery that insects can adapt to these toxins raises concerns about the long-term usefulness of B.t. toxins. Several methods for managing the development of resistance to B.t. toxins have been suggested, but none of these approaches offer clear advantages in all situations.