Naïve Pine Terpene Response to the Mountain Pine Beetle (Dendroctonus ponderosae) through the Seasons.

Insect herbivores must contend with constitutive and induced plant defenses. The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae, Scolytinae) has expanded its range east of the Rocky Mountains into the western boreal forest and is encountering evolutionarily naïve lodgepole pines (Pinus contorta) and jack pines (Pinus banksiana). Pinus contorta and P. banksiana in the expanded range have different constitutive and induced defenses in response to wounding and inoculation with fungal associates of D. ponderosae. In the historic range, previous studies have examined phloem terpene content prior to and just after D. ponderosae mass attack, but the terpene profile of attacked trees post-overwintering is unknown. We examined the response of mature P. contorta and P. banksiana trees to experimentally-applied mass attack by D. ponderosae and quantified phloem terpenes at three time points, pre-attack, post-attack (same season), and the following spring, post-overwintering. Phloem content of total terpenes as well as many individual terpenes increased after D. ponderosae attack but were only significantly higher than pre-attack levels at the post-overwintering time point in both P. contorta and P. banksiana. The absence of a significant increase in phloem terpenes in the month following attack in naïve pines is a potential cause for increased D. ponderosae offspring production reported in naïve P. contorta. Beetle attack density did not influence the phloem terpene profiles of either species and there was no significant interaction between attack density and sampling time on terpene content. High phloem terpenes in trees that are attacked at low densities could prime these trees for defense against attacks in the following season but it could also make these trees more apparent to early-foraging beetles and facilitate efficient mass attack at low D. ponderosae population densities in the expanded range.

Aggregation and a strong Allee effect in a cooperative outbreak insect.

Most species that are negatively impacted when their densities are low aggregate to minimize this effect. Aggregation has the potential to change how Allee effects are expressed at the population level. We studied the interplay between aggregation and Allee effects in the mountain pine beetle (Dendroctonus ponderosae Hopkins), an irruptive bark beetle that aggregates to overcome tree defenses. By cooperating to surpass a critical number of attacks per tree, the mountain pine beetle is able to breach host defenses, oviposit, and reproduce. Mountain pine beetles and Hymenopteran parasitoids share some biological features, the most notable of which is obligatory host death as a consequence of parasitoid attack and development. We developed spatiotemporal models of mountain pine beetle dynamics that were based on the Nicholson-Bailey framework but which featured beetle aggregation and a tree-level attack threshold. By fitting our models to data from a local mountain pine beetle outbreak, we demonstrate that due to aggregation, attack thresholds at the tree level can be overcome by a surprisingly low ratio of beetles per susceptible tree at the stand level. This results confirms the importance of considering aggregation in models of organisms that are subject to strong Allee effects.

Factors Influencing Male Plutella xylostella (Lepidoptera: Plutellidae) Capture Rates in Sex Pheromone-Baited Traps on Canola in Western Canada.

Optimization of male moth trapping rates in sex pheromone-baited traps plays a key role in managing Plutella xylostella (L.). We investigated various ways to increase the attractiveness of pheromone-baited traps to P. xylostella in canola agroecosystems in AB, Canada. Factors tested included pheromone blend and dose, addition of a green leaf volatile to the pheromone at different times during the season, lure type, trap color, and height. The industry standard dose of 100 µg of pheromone (four-component blend) per lure (ConTech Enterprises Inc., Delta, British Columbia [BC], Canada) captured the most moths in the two lure types tested. Traps baited with pheromone released from gray rubber septa captured more males than those baited with red rubber septa. Traps baited with lures in which Z11-16: Ac is the main component attracted significantly more moths than those in which Z11-16: Ald is the main component. The addition of the green leaf volatile, (Z)-3-hexenyl acetate, to pheromone at a range of doses, did not increase moth capture at any point during the canola growing season. Unpainted white traps captured significantly more male moths than pheromone-baited traps that were painted yellow. Trap height had no significant effect on moth capture. Recommendations for monitoring P. xylostella in canola agroecosystems of western Canada include using a pheromone blend with Z11-16: Ac as the main component released from gray rubber septa at a dose of 100 µg.

Assessment of commercially available pheromone lures for monitoring diamondback moth (Lepidoptera: Plutellidae) in canola.

Sex pheromone monitoring lures from five different commercial sources were compared for their attractiveness to male diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) in canola, Brassica napus L., fields in western Canada. Lures that had the highest pheromone release rate, as determined by aeration analyses in the laboratory, were the least attractive in field tests. Lures from all the commercial sources tested released more (Z)-11-hexadecenal than (Z)-11-hexadecenyl acetate and the most attractive lures released a significantly higher aldehyde to acetate ratio than less attractive lures. Traps baited with sex pheromone lures from APTIV Inc. (Portland, OR) and ConTech Enterprises Inc. (Delta, BC, Canada) consistently captured more male diamondback moths than traps baited with lures from the other sources tested. In two different lure longevity field trapping experiments, older lures were more attractive to male diamondback moths than fresh lures. Pheromone release from aged lures was constant at very low release rates. The most attractive commercially available sex pheromone lures tested attracted fewer diamondback moth males than calling virgin female moths suggesting that research on the development of a more attractive synthetic sex pheromone lure is warranted.

Efficacy of Chlorantraniliprole Seed Treatments Against Armyworm (Mythimna unipuncta [Lepidoptera: Noctuidae]) Larvae on Corn (Zea mays).

Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae) is an important insect pest of corn (Zea mays L.) in North America and can cause severe damage during outbreaks. Insecticides are the main control method; however, development of insecticide resistance poses management challenges and necessitates the use of novel insecticides. A synthetic insecticide, chlorantraniliprole, belonging to the anthranilic diamides, targets insect ryanodine receptors and is a potential alternative to conventional insecticides for management of M. unipuncta. We determined the efficacy of seed treatment with chlorantraniliprole alone compared with a positive control consisting of a neonicitinoid seed treatment of thiamethoxam and combinations of both compounds against M. unipuncta larvae in laboratory bioassays. Bioassays were conducted on two different growth stages of M. unipuncta larvae (instars 3 and 5) and two plant growth stages (V1 and V2 corn) in clip cages and whole plant experiments. Larval mortality, head capsule width, and feeding injury were measured. The chlorantraniliprole seed treatment alone or in combination with thimethoxam at different doses affected survival of M. unipuncta larvae. In all bioassays except one, larval mortality occurred earlier when a combination of chlorantraniliprole and thimethoxam seed treatment was used when compared with a thimethoxam alone seed treatment. Mythimna unipuncta larvae developed faster on the untreated control corn plants compared with corn with insecticide seed treatments. Foliar injury was low in both chlorantraniliprole alone and chlorantraniliprole + thimethoxam treatments compared with the control. Chlorantraniliprole thus offers potential alternative to conventionally used insecticides in the management of M. unipuncta in corn.

Disruption of pheromone communication of Choristoneura rosaceana (Lepidoptera: Tortricidae) using microencapsulated sex pheromones formulated with horticultural oil.

Sprayable, microencapsulated (MEC) sex pheromone formulations represent a promising tool for achieving mating disruption, yet often lack sustained effectiveness in the field, making repeated applications necessary. This study evaluated the impact of adding Purespray Green horticultural oil as an adjuvant to 3M MEC-LR, an MEC formulation of (Z)-11-tetradecenyl acetate, on disruption of mate-finding behavior in Choristoneura rosaceana (Harris) in small-plot trials in experimental apple orchards. Treatments consisting of MEC-LR in water, MEC-LR in water + 2% (vol:vol) Purespray Green, and a water control were applied to plots of apple using an airblast sprayer at a rate of 100 g of pheromone/ha. Disruption caused by foliar treatments was evaluated over a 7-wk period using mark-release recapture experiments in the field and concurrent bioassays in a flight tunnel. Disruption of orientation to 2-d-old, calling, virgin females was used as a measure of treatment effect in all experiments. Both pheromone alone and pheromone + oil treatments significantly disrupted male mate-finding behavior for a period of > or =21 d in flight tunnel assays and > or =42 d in mark-recapture field trials. The addition of oil did not significantly enhance the disruption activity nor increase the longevity of the MEC pheromone formulation. Our results show the compatibility of spraying MEC pheromone with a horticultural oil, and techniques for applying an oil-pheromone formulation to maximize the control impact of this combination are discussed.

Resource Allocation to Flight in an Outbreaking Forest Defoliator Malacosoma disstria.

Allocation of larval nutrients affects adult life history traits in insects. This study assessed the effect of moth age and wing loading on flight capacity in an outbreaking forest lepidopteran, Malacosoma disstria Hübner . Insects were collected from high and low density populations after larval feeding, and flight capacity was tested directly with flight mills and indirectly through the allometric relationship between wing area and body size. Insects from these same populations collected as eggs and fed with a synthetic diet in the laboratory were tested in a separate experiment. Male moth propensity to fly increased with wing loading only when moths were collected as pupae after feeding in the field at high population densities. Moth age and wing loading did not affect the distance flown by male moths in any of the population density-nutrient regime combinations tested. Energy use increased with flight distance in both experiments. The slope of the allometric relationship between wing area and body mass did not differ from isometry when moths were collected as pupae after feeding at low and high population densities in the field. The slope of this relationship was steeper for males collected from high than low population densities. There was no allometric relationship between wing area and body mass of moths collected from these same populations as eggs and fed ad libitum in the laboratory as larvae. The results suggest that male M. disstria can allocate resources to different life history traits in response to differences in population density.

Factors influencing flight capacity of the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae).

The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae) is the most damaging pest of mature pine (Pinaceae) in western North America. Although mountain pine beetles have an obligate dispersal phase during which adults must locate a new host for brood production, dispersal is a poorly understood aspect of its ecology. This flight mill study was designed to test the effects of beetle size, sex, and age on flight capacity. Energy use during flight was assessed through measurements of weight before and after flight and fat content of flown versus control beetles. The mean flight distance achieved by mountain pine beetles varied between 2.12 and 5.95 km over the 23-h bioassay, but the longest total flight of an individual beetle was >24 km. Beetle preflight weight influenced flight initiation, flight distance, and duration. Bigger beetles are more likely to fly and once in flight fly longer and farther than smaller beetles. There was no direct effect of beetle sex on flight capacity. Flight capacity of beetles declined with age postemergence. Although individual flight capacity was variable, flight velocity was relatively constant between 1.55 and 1.93 km/h. Lipids are used to power flight in mountain pine beetles, as lipid content was lower in beetles flown on the flight mills compared with beetles that did not fly. Flight distance was negatively correlated with beetle postflight lipid content. The baseline flight capacity data revealed in this study have implications for understanding the population dynamics of this eruptive forest pest.