The distribution, larval survival, and impact of a tip moth guild (Lepidoptera: Tortricidae: Rhyacionia specia) in the Northern Plains

Graduation date: 1993A guild of three and possibly five tip moths\ud (Rhyacionia spp.) occurs on ponderosa pine (Pinus ponderosa)\ud in southeastern Montana, northwestern South Dakota, and\ud southwestern North Dakota. Trapping results indicated that\ud many of these species may be flying simultaneously, and\ud individual species relative abundances showed west-to-east\ud trends.\ud Tip moth larvae became increasingly concentrated in the\ud tops of trees as the summer progressed. A significant\ud percentage of larvae in infested shoots were parasitized or\ud died before pupating. Parasitism rate was higher in larvae\ud collected later in the growing season. Tip moth larval\ud survival rate was affected by larval location within the\ud tree and the date of collection.\ud Seedlings and saplings studied had fewer branches on\ud average than ponderosa pines in other regions. The percent\ud of apical shoots infested per tree (API) was strongly\ud correlated with the total percent of shoots infested per\ud tree (PI) as long as API was less than 50%. Neither API nor\ud PI was strongly correlated with total linear shoot growth\ud (linear growth). Linear growth was affected by tree\ud deformity and available site moisture. Wetter sites also\ud had higher mean PI.\ud Aspect, slope, regenerating tree density, horizontal\ud configuration, topography, and habitat types were examined\ud for effects on tip moth activity. Impact measures such as\ud API and PI were not strongly affected by these\ud characteristics. PI appeared to be higher in areas that\ud retain moisture, i.e. concave or horizontal land form, than\ud in areas that do not, i.e. convex or slope land form.\ud Abundant precipitation may mask this relationship.\ud Management implications are discussed