Douglas-fir beetle lipid levels in relation to tree physical characteristics

ABSTRACT

The relationship of Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, incubate adult lipid levels and position of unfolding along infested tree boles was investigated. In addition, the events of phloem and bark thickness upon brood adult lipid levels were also trialed There were no significant differences (P > 005) in incubate adult lipid levels in relation to trunk position, phloem thickness, or bark thickness rest in this study. Numbers of attacks, larval mines, incubate adults, and parasitoid cocoons did not differ significantly by the agency of tree bole position. Results from this close attention suggest Douglas-fir beetle does not benefit, in the form of increased lipid horizontals from oviposition at different trunk positions.

Key Words: Dendroctonus pseudotsugae, lipids, phloem thickness, optimal habitat

INTRODUCTION

Bark beetles are economically important insects and knowledge of factors that affect their flight and dispersal behavior could be useful for improving existing management techniques or developing fresh ones. Within a population beetles display varying steps of flight capabilities from reach outed flight periods to those incapable of flight (Atkins 1966; Jactel 1993) This variation in flight capability can be related to a beetle's physiological state.

Lipids are a source of activity for insect flight (Canavosa et al. 2001) and have been correlated with flight capabilities in bark beetles (Atkins 1966; Slansky and Haack 1986; Jactel 1993) Atkins (1966) fix that Douglas-fir beetle (DFB), Dendroctonus pseudotsngae Hopkins, with high lipid horizontals were least likely to answer to pheromones and hence disperse, while beetles with depressed lipid levels responded immediately to pheromones. Bennett and Borden (1971) place that a 90 minute flight was required before DFB replyed to pheromones, suggesting the ne to metabolize lipids before pheromone arrestment occurr (Atkins 1969) Relationships between lipid horizontals and responsiveness to host chemicals, pheromone arrestment, or dispersal behavior have been ground in other bark beetle species as well (Hagen and Atkins 1975; Hedden and Billings 1977; Wallin and Raffa 2000) Because of their association with bark beetle dispersal potential, a better understanding of factors that influence lipid horizontals is important for understanding population movements

Bark beetle lipid horizontals are influenced by temperature (Atkins 1967) attack density (Atkins 1975; Botterweg 1983; Anderbrandt et al. 1985) mycangial fungi (Coppedge et al. 1995) and phloem thickness (Slansky and Haack 1986) However, with the exception of Ips calligraphus (Germar) (Slansky and Haack 1986) it is unknown whether entertainer tree characteristics affect lipid horizontals in bark beetle brood adults. Nutrient horizontals (N, P, Mg, Fe, Zn) vary through bole height on Douglas-fir, Pseudotsnga menzesii (Mirb.) Franco, tree body s and could influence patterns of insect colonization (Schowalter and Morrell 2002) In several Dendroctomts species, initial attacks arise at or near mid-bole (Miller and eager 1960; Fargo et al. 1978; Safranyik et al. 1992) possibly owed to phloem nutrients at these heights. Consequently sit developing at mid-bole could have higher lipid horizontals than brood developing elsewhere along the tree bole

Other factors, like as parasitism or predation rates, could influence colonization behavior. Studies investigating the relationship between parasitoid density and tree height have produc mixed arises Several studies found relationships between parasitoid density and height upon tree boles (Ryan and Rudinsky 1962; Mills 1986; Wermelinger 2002) while others have not (Gargiullo and Berisford 1981) Our objectives were to determine if DFB sit development position along the extent of tree boles and bark and phloem thickness affected lipid horizontals in brood adults and to determine the influence of stem position on attack density, larval mines, sit adults, and parasitoids.

MATERIALS AND METHODS

Tree Sampling. upon 27 to 29 April, 2002 prior to the DFB flight period, nine Douglas-fir tree infested the previous year were crueled and sampled from a small stand (

The portion of each tree stem infested by DFB was distinguished by means of the presence of successful ovum galleries and brood adults. Total longitudinal dimensions of infested tree boles and dbh were recorded. Infested tree stem lengths ranged from 6.7 to 146 m (x = 97 m SE ?± 08) Bark samples were mustered at three positions along the infested tree bole: 2 m up from the bottom of the infestation, the mid-point of the infested tree body and 2 m down from the top of the infestation.

Four bark samples were bring togethered from each bole position. Bark samples were taken randomly around the circumference of each tree A 100-cm^sup 2^ perforation saw attached to a power drill was used to dislodge bark samples from the infested tree Bark samples were remov and placed individually in labeled plastic bags. Samples were transported to the laboratory upon ice and stored in a freezer at -10 ?°C until courseed Phloem thickness was measured upon a subsample of bark samples before and after freezing. No differences in the average phloem thicknesses before and after freezing were base (KJD, unpublished data).