Resistance of Ponderosa Pine to 

 the Gouty Pitcli Midge 

 {Cecidomyia piniinopis) 



R. J. Hoff 



INTRODUCTION 



In 1985 a heavy infestation of the gouty pitch midge 

 (Cecidomyia piniinopis) was found in a plantation of 

 ponderosa pine (Pinus ponderosa) in northern Idaho. The 

 trees had been planted in rows of four trees, each row 

 representing one family. It thus became apparent that 

 some families were heavily damaged while others were not 

 damaged at all. 



The purpose of this paper is to document severity of 

 infestation, and inheritance of resistance to midge attack 

 in a ponderosa pine plantation in the Inland Northwest. 



The gouty pitch midge is a native pest of forests of 

 Eastern and Western North America. In the West, the 

 pest is especially injurious to ponderosa pine where the 

 level of infestation becomes high enough to kill trees 

 (Eaton and Yuill 1960). Natural controls such as weather, 

 host resistance, and parasites normally keep it in check 

 (Eaton and Yuill 1960). The midge lays its eggs on rapidly 

 growing branch and leader tips. After hatching, the larva 

 bores through the surface until it is completely embedded 

 in the vascular tissue. The larva feeds there until the 

 following spring, then works to the surface to pupate. The 

 adult emerges in 10 to 14 days. Damage occurs during 

 larval feeding, the result of disruption of vascular tissue. 



The level of midge infestation appears to be associated 

 with the characteristics of the new shoots (Austin and 

 others 1945). Shoots that are smooth or are covered with a 

 waxy bloom are less infested than shoot surfaces that are 

 sticky and resinous. Further, Duffield (1985) reported 

 evidence that the nature of the new shoot surface was 

 inherited and that two genes were involved. 



MATERIALS AND METHODS 



In 1974 the Northern Region of the Forest Service 

 established two progeny tests of ponderosa pine in north- 

 em Idaho and one in western Montana. Other members of 

 the Inland Empire Tree Improvement Cooperative also 

 established tests the same year. Altogether there are six 

 plantations. In 1985 the plantation at the Lone Mountain 

 tree improvement site in northern Idaho exhibited high 

 infestation by the gouty pitch midge (fig. 1). 



The Lone Mountain tree improvement site is located 40 

 km north of Coeur d'Alene, ID. The site is flat, with only 

 slight undulations, at an elevation of 758 m. The entire 

 65-ha site is surrounded by naturally regenerated ponder- 

 osa pine and lodgepole pine (Pinus contorta), with lesser 



amounts of grand fir (Abies grandis), Douglas-fir (Pseu- 

 dotsuga menziesii), and western larch (Larix occidentalis). 

 This natural stand has an overstory of mature scattered 

 trees (remnants of harvest) and an understory of pole-sized 

 trees 6 to 9 m tall. Many ponderosa pine of all ages were 

 infested with the gouty pitch midge. 



Open-pollinated seed of 234 families were collected from 

 48 stands located in northeastern Washington and in 

 Idaho north of the Salmon River. The number of trees per 

 stand was usually five, sometimes four. The seedlings 

 were grown at a Forest Service nursery near Coeur 

 d' Alene, ID, in bare-root beds for 2 years, then lifted and 

 planted at the Lone Mountain site in April 1974. The 

 experimental design was a randomized complete block 

 design with five blocks. Four progeny of each family were 

 planted per block as a four-tree row plot. 



Data were taken by estimating the number of dead or 

 dying branch or leader tips. The range of damaged tips 

 was determined by spending a couple of hours counting 

 damaged tips throughout the test on several trees. From 

 this inspection a scoring system was developed that would 

 encompass all trees. Then the level of infestation of each 

 tree was noted and placed in one of the following classes: 







= 



infested branch or leader tips, average 



= 



1 



= <5 



infested branch or leader tips, average 



= 2.5 



2 



= 6-32 



infested branch or leader tips, average 



= 18 



3 



= 33-67 



infested branch or leader tips, average 



= 49 



4 



= 68-100 



infested branch or leader tips, average 



= 84 



Tree height varied from 1.1 to 7.0 m; to determine the 

 proportion of tips damaged on a tree basis a regression of 

 the actual number of tips per tree (healthy and damaged) 

 by height was determined. A random sample of 224 trees 

 (6 percent of total trees) was selected to develop the 

 regression formula. The data used for analysis were the 

 percentage damage per tree, determined as follows: 

 percent damage = number of damaged tips/TT where TT = 

 a + bx, and TT = estimated total tips, x = tree height, a and 

 b = regression coefficients, number damaged = the average 

 associated with the field damage category. Because 

 percentage of damage varied widely, these data were 

 transformed (arcsin V percent) (Steel and Torrie 1960). 



The analysis of variance model and expected mean 

 squares are shown in table 1. Heritabilities followed 

 Namkoong (1979). The relationship of gouty pitch midge 

 damage to 1985 height was determined by regression 

 analysis, using the GLM procedure (SAS 1979). 



1 



