ARTHROPODS ASSOCIATED WITH THE GIANT SEQUOIA
Ronald E. Stecker
Relatively little scientific study had been made on the arthropods associated with the giant sequoia prior to this study. Only 20 insect species had been identified in association with this tree, and there was virtually no specific information available to suggest the total arthropod fauna or its effect upon this immense and ancient host. The first reference to insects associated with giant sequoia was by Hopkins (1903) who listed six species. The most authoritative publication on the giant sequoia of this early period with some mention of insects was that by Judge Walter Fry, U.S. Commissioner of Sequoia National Park, and Colonel John White, Park Superintendent (Fry and White 1930). Person (1933) briefly discussed two new insects associated with the giant sequoia. Keen (1938 rev. 1952) mentioned four insects in his original publication (and eight in the revised). Phymatodes nitidus, a central figure in this study, was reported in that publication to be a bark boring beetle.
DeLeon (1952) presented the most recent and complete review of sequoia insects. His paper is important as it named 20 insects which may use giant sequoias to complete some aspect of their life cycle. He also suggested the possible association of Phymatodes nitidus with the cones of giant sequoia. The preceding reports make up the limited entomological references to giant sequoia prior to 1966. This and the following chapter are a result of nearly 10 years of studies attempting to expand the body of knowledge concerning the arthropod fauna of the giant sequoia. Chapter 7 is concerned only with those insects that affect reproduction of giant sequoias.
Detailed investigations of the invertebrates of downed trees, seedlings, and living trees with foliage accessible from the ground were initiated in 1966 following observation by Hartesveldt and Harvey (Hartesveldt et at. 1975) that 3.5% of the seedlings in their study plots were being killed by chewing insects. In the summer of 1967 the research was moved from the ground into the tops of mature living trees in order to further determine the biotic interrelationships between the arthropods and the giant sequoia. Trees that were free-climbed were studied from 1967 to 1974 in Redwood Mountain Grove, Whitaker's Forest, Converse Basin, Mt. Home State Forest, and many other locations in Sequoia and Kings Canyon National Parks. An elevator was rigged for investigation of arthropod life in the tops of two mature trees (Fig. 44), hereafter called the Albina Tree (studied in 1967) and the Castro Tree (studied in 1968-74).
The objectives of this part of the study were to answer several questions. What are the arthropods hosted by this tree? What ecological role do they play with the host? Are any species host-specific to the giant sequoia?
Most of the investigations discussed in this chapter were carried out in Redwood Canyon (Ridge, North, Trail, and South Study Areas), Redwood Mountain (NPS environmental burn zone) and Whitaker's Forest, a University of California/NPS field research station (Fig. 4). Some sampling was conducted in the Converse Basin and Mountain Home groves outside of Kings Canyon National Park. The four major objects of this study were: 1) seedling insects, 2) arthropods of downed trees, 3) those of free-climbed trees, and 4) those of elevator-rigged trees.
Most of the insects found on seedlings had effects on seedling reproduction (see Chapter 7), hence only the aphid study will be reported here.
Forty-one seedling plots used in the study were seeded artificially or by natural seedfall. All of the plots were established in Redwood Canyon or on Redwood Mountain. Three plots (3 m x 3 m) were used in the summer of 1968; 10 plots in 1969 and 28 plots in 1970. all of uneven size and naturally seeded after fires. These plots, described in detail in Chapter 7, were studied primarily for insect activity and only secondarily as to seedling survival. Two geometrids, a gryllacridid and an aphid were investigated. The aphids were observed with a 10 power hand lens at eye-level to the ground. Paper rings 62 mm across, coated with "stickum," were placed around the bases of seedlings, but were unsuccessful when defoliators crawled through the central hole and escaped the adhesive trap. Frass collected on the discs, however, aided in determining identifications and frequency of defoliators.
Studies of downed trees
Arthropods were collected from sequoias that had been down from 1 to 15 years or more. Specimens were cut out from under bark and xylem by axe and steel bar. Whenever possible, limbs and pieces of the bole were retained for rearing studies of the immature insects for positive identification of adults and for parasite and predator studies. They were housed in sealed cardboard boxes which had small jars as collecting windows or traps. Metal 18.9 liter (5 gal) cans were first tried, but presented mold problems and were discontinued. Some late instar larvae and pupae were kept in rearing vials of 12.7 cm (5 in) test tubes to obtain adults.
Free-climbed tree studies
Studies reported in this section involved approximately 30 trees from pole-size to over 60 m (200 ft), entered from the ground with little or no rope work. Most of these sequoias were in Redwood Canyon, Whitaker's Forest, Converse Basin, and Mountain Home State Forest south of Sequoia National Park. These trees ranged from 15 to approximately 200 years old and were all spire-topped. Access to several trees required establishing a prussik rope over the first sound limb at about 7.5 m (25 ft). Climbing without ropes was routine after one reached a point in the tree where the limbs were usually a meter or less apart, gradually becoming closer towards the top. Standardized numbers of sweep samples were made of the foliage with a sweep net. Sweeps consisted of sampling three linear feet of foliage using a 7 cm (18 in) net, a technique which proved most helpful in counts of Homoptera and Hemiptera. All larval forms secured from the sweeps were housed in paper and plastic bags for rearing to the adult stage in hopes of finding parasites. Hundreds of cones were secured from several dozen trees for paper bag rearing of insects and dissection of cones.
Rigging of elevator in study trees
Access into the crown of mature giant sequoias is made difficult by the immense butt swell, the large near-ground diameter (15-27 ft) and the great distance from the ground to the first limbs, from about 27 m to 46 m (90 to 150 ft). Entry into the tops of living giant sequoias was accomplished with the help of Charles Castro of the National Park Service. Castro, utilizing climbing techniques which he developed to suppress lightning caused fires in the crowns of large trees, rigged two giant sequoias (called the Albina and Castro trees in this study). This was accomplished by climbing large fir or pine trees adjacent to (within 23 m [75 ft]) the selected study trees. The smaller tree was scaled using 8.9 cm (3-1/2 inch) tree gaffs or timber spikes, climbing belt and circumference ropes. The latter were dual 1.9 cm (3/4 inch) manila ropes permanently secured to a right "D" ring attached to a "Bashling 60 FH" climbing belt. They were used around the tree and were secured to the left "D" ring by means of a "Tenzalok" rope-lock device. One rope was used at a time to bypass branches. This technique was used to take the climber to between 46 m and 61 m (150 to 200 ft) in the smaller access tree to a point 15 m to 24 m (50 to 80 ft) above a major limb of the sequoia. Limbs facing the sequoia were removed from the access tree up to the point of attachment of a pendulum line which passed around the bole and over several limbs at the upper most point scaled in the access tree. This line was 1.3 cm (1/2 in), four-strand manila tree surgeon's climbing rope, 46 m to 91 m long (150 to 300 ft). The climber then exchanged belt and spurs for a "Buckingham" tree saddle which allowed the climber to arc on a prusik dropline until he secured a hand hold on the end of a major sequoia limb (usually 40+ meters from ground level). After releasing the rope from the access tree he climbed to the 76 m (250 ft) level of the sequoia by prusik rope. An electric elevator (Albina Hi-Climber) terminal attachment was secured for easy daily access.
The rigging was modified when using the same tree two or more years in a row. Old ropes were left in the Castro Tree at the 43, 64, 73, and 85 m (140, 210, 240, and 280 ft) levels with the lowest rope reaching the ground. The following year new climbing rope was tied to the old, pulled through to replace the old, and used as entry to the elevator attachment point, where a 1.3 cm (1/2 in) steel cable was wrapped around the tree, with looped ends receiving the 8.4 mm (5/16 in) cable which is attached to an elevator at rest near the base of the giant sequoia. The elevator was powered by a six h.p. gasoline-operated five K.V.A. alternator stationed on the ground. A safety bull line was provided along the path of the elevator to which occupants were attached by a short sliding rope. The elevator ascended and descended at 4.5 m (15 ft) per minute. Phyllis Stecker, wife of the writer, operated the power source as well as fed and recoiled the 76 m (250 ft) power cable to the maneuvering Hi-Climber during the operation. The Hi-Climber was fitted with a shield-shaped skid designed by Harvey (Fig. 44) to eliminate excessive wear of the tree and to prevent the rig from fouling in the limbs and minimized removal of limbs along the vertical path of the device.
The investigator could either swing pendulum-like or walk out to ends of branches by means of prusik ropes [1.27cm (1/2 in), four-strand manila] 91 m (300 ft) or less in length looped basally over ends of 15 cm (6 in) of larger limbs. The longer the drop line, the easier was the task of reaching the ends of these branchessome nearly 15 m (50 ft) off center. Figure 45 illustrates this technique on one of the shorter crown branches. In 1974 the use of four-strand manila rope was discarded for a synthetic three-strand called "Silvalon." This rope is very superior because of its three fold greater strength and ease of handling.
Methods of sampling mature trees
Sampling sequoia foliage presents unique problems. Several techniques were adapted from existing methods of ground sampling to reliably assess insect activity in the crown of living trees. Modified malaise traps (Butler 1965) and sticky boards (Roesler 1953, modified by Wilde 1962) were used during the study of the Albina Tree in 1967, and the first year in the Castro Tree in 1968. The malaise traps were constructed of war surplus mosquito nets designed to cover cots (Fig. 46). Two-thirds of one side were removed to allow insects access to the sloping, inner retainer wall. Negative geotropic response led insects up the slight incline of the inner roof of the net and through a cardboard funnel into a large plastic collection bag. Loose, fluffed paper tissue was included in the bag to take up any moisture that developed on the walls of the bag, and to keep insects from damaging each other by abrasion. Guy lines were somewhat difficult to position because of the moving branches, but the major problem was the predation upon captured insects by spiders within the plastic collection bags. Cyanide and other killing agents were tried to control the spiders but the best results came from servicing the traps once or twice a day. Malaise traps were placed at 15 m (50 ft) intervals within the 30 m to 88 m (100 to 290 ft) level of the two trees. Material secured from these traps did not necessarily come from the sequoia host but provided a starting point for insect study by gross collecting of fauna within the sphere of the tree. In addition, 60, 3cm (1/4 in) thick adhesive boards, of 929 cm2 (1 ft2) of yellow surface per side were coated with a film of "Stickum Special," a commercial preparation for mechanical insect control. Boards, with 1.6 mm to 2.2 mm (1/16 to 1/8 in) of coating, were placed at all elevations and on all sides of the tree. They were further assorted and oriented as to north-south or east-west facing alignment, and horizontal versus vertical aspect within each of these subareas of the tree. The sticky boards were very successful in that they provided greater information as to kind and general location of insects within the tree. Relative numbers through time were also established by their use.
The most important method of locating and studying exposed insects was by direct observation. The investigator could move within any portion of the tree, using drop lines, and carefully observe the activity and behavior of insects in the tree's branches.
Over 10,000 insects were collected during these investigations. They were mounted and labeled in the field by Phyllis Stecker and are housed in the Museum of Entomology, San Jose State University, San Jose, California. A reference collection of insects of the giant sequoia (and of the general area) is maintained there. Identification of these insects has been by the author and by recognized authorities of the various insect groups whenever possible. These arthropods were then analyzed as to their ecological and physical relationship within their host.
One hundred forty-three species of insects and seventeen species of other arthropods were identified as using the giant sequoia as a host (food or substrate) during some portion of their life cycle (see Appendix II for listing). Information secured from the study of the arthropods found on seedlings, downed trees and living sequoias is discussed within an ecological famework in this section.
Malaise traps and sticky boards provided broad leads as to some of the insect fauna of the standing trees. Insects caught on sticky boards were hard to clean, even with xylene solvent, while a different problem, that of spider predation, was encountered with the malaise traps. These techniques were discontinued by the end of the second year in favor of sweeping and concentrated observation of the tree canopy.
In general, the abundance of flying insects was associated with that portion of the canopy in full sunlight, or east to west sectors from sunrise until sunset. A vertical arrangement of insects in such a tall tree was suspected, but it was soon obvious that this was not the case.
Insects of seedlings
Very few insects were found to be associated with seedlings three years of age and less. Two geometrids and a gryllacridid were found and are discussed in Chapter 7 as insects related to reproduction of giant sequoia. In 1970 an aphid, Masonaphis morrisoni, was common on first year seedlings (Fig. 47). Forty-four percent of the seedlings from 28 plots (numbered 14-41) ranging in size from 18 to 72 mm had aphid activity averaging 1.6 aphids per seedling of those with aphids (plots 1-13 from 1969 were not studied for aphids). This was the first record of the male morph of this species, thus only four species of insects are known to use the seedling stage of giant sequoia.
Insects of downed trees
Arthropods were studied on trees down from several weeks to over 20 years. Callidium sequoiarum, a cerambycid beetle known only from this host (DeLeon 1952), was commonly found in fresh down limbs with Semanotus ligneus amplus (Cerambycidae) (DeLeon 1952). Both beetles mine as larval stages beneath bark less than 2 cm thick. The latter was also associated with a rodent-killed, pole-size sequoia in the Cherry Gap Grove of Sequoia National Forest in 1966 (Shellhammer et al. 1970). Temnochila virescens (Ostomatidae) and Cucujus clavipes (Cucujiidae) were predatory as adults and larvae on the two cerambycids. A small, 6 mm long, cricket commonly called the west coast ant cricket, Myrmecophila oregonensis (Gryllidae), was found under moist bark in association with the cucujid pupal chambers. The ant cricket usually lives in a commensal state with various species of ants. An ambrosia beetle, Gnathotrichus sulcatus (Scolytidae), was recorded by DeLeon (1952) from trunk sapwood. It was commonly found there in the present study as well as in limbs of recently downed giant sequoia sapwood. Larvae and fresh adults of Sirex areolatus, a horntail (Siricidae), were retrieved from mines over one decimeter deep in heartwood of a tree which had been down for nine months.
More insects were associated with sequoias that were down for over one year than in those down less than one year (see Appendix II for complete listing). Among those found over one year were: Trachykele opulenta (Buprestidae) which as larvae mine 10 cm into the xylem forming horizontal pupal chambers, and stag beetles, Ceruchus puntatus (Lucanidae). The former beetle can kill trees undercut by streams or otherwise mechanically damaged or suppressed.
Rhysodes hamatus (Rhysodidae), or wrinkled bark beetles, which normally use beech, ash, elm, and other deciduous trees, and at times pines (Arnett 1960), for a host, were discovered under the bark of sequoias (which aids in further establishing this small beetle's relationship with coniferous hosts). Several wood-boring, but not wood-feeding, Hymenoptera were noted in downed sequoias. Carpenter ants, Camponotus minor (Formicidae) were commonly noted in stumps and in portions of logs at ground contact. Carpenter bee, Xylocopa californica (Xylocopidae), damage to downed sequoia was noted but no individuals were actually found. Drywood termites, Zootermopsis navadensis (Kalotermitidae), were also found feeding on downed sapwood and larger dried-out limb joints.
Two neuropterous predators were noted in larval mines and under bark. Agulla assimilis (Raphidiidae), a snakefly, was the most common. The snakefly larvae were also found in the old emergence holes. Chrysopa carnea (Chrysopidae), or green lacewings, were collected as larvae beneath the bark of downed trees. This insect is normally an aphid feeder ("aphid lion") and was thought to be feeding on small invertebrates or, quite possibly, using the location as a pupation site.
Anoplodera valida, a long-horned wood-boring beetle (Cerambycidae), was secured in the larval stage mining a 30 m (100 ft) downed sequoia in Whitaker's Forest.
The following beetles were found under the bark of downed sequoias: Nyctoporis carinata and Uloma loingula (Tenebrionidae), scavengers under bark; and Trigonurus sp. (Staphalinidae), predators under bark and numerous in brown cones on the ground from Trail Area. Lycidota california (Lampyridae) was a predator under bark, and Ptinus agnatus (Ptinidae) was found under loose bark and reared from small dead limbs of mature sequoias.
One of the more common insects found in sequoias down for 10 to 20 years or more was Melasis rufipennis (Melasidae). These small beetles were noted in densities up to 90/dm2 mining old sapwood. Their old emergence holes indicated activity in past years.
Insects of standing live trees
The arthropod fauna of living giant sequoias, unstudied before this project, offered the greatest wealth of new information. Insects with sucking mouth parts were especially numerous. Eleven out of a total of 74 insects found in the canopy of living trees had this type of feeding style. Insects that attack one to three year old giant sequoias are discussed in Chapter 7
The following insects were among those found associated with sequoias between 3 and 25 years of age. Two plant bugs (Miridae), Lygus hesperus and an unidentified form, were commonly observed feeding on new foliage. Dichelonyx vicina (Scarabaeidae) actively fed upon sequoia foliage of this age group, as did Sitona california and Apion sp. (both Curculionidae). The weevils were not observed in mature trees. Scobicia declivis (Bostrichidae) and Anthaxia aneogaster (Buprestidae) were secured by sweeping the foliage of this age class. DeLeon (1952) records the latter from recently broken limbs infested with Callidium sequoiarum. Large leaf beetles, Glyptoscelis juniperi xanthocoma (Chrysomelidae), were observed feeding and were swept from foliage of sequoias at most study sites.
Sequoias 25 years and older, including the over 1,000 year old Castro and Albina elevator-rigged study trees, yielded the following insects. Five species of leafhoppers (Cicadellidae) were discovered actively feeding on new terminal foliage. The most common were Balclutha medius, Idiocerus musteus and I. apache, while I. amoenus and I. nervatus were found in smaller numbers. Three treehoppers (Membracidae) were secured by adhesive board traps in 1967 and were confirmed as feeding on new foliage throughout the tree from 1968 to 1970. The species were Crystolobus nitidus Van Dyke, Micrutalis occidentalis and Platycotis minax. Adult snakeflies (Raphidiidae), Agulla assimilis, were observed feeding on B. medius. A small psyllid, Psylla brevistigmata (Psyllidae), was secured throughout the study trees by sweeping foliage.
Other fluid-feeding insects included Ischnorrhynchus resedae (see Chapter 8) which fed as adults on new tissue in the upper one-third of the older trees, and Neides muticus (Berytidae-Neididae), a stilt bug, commonly found both in young and old trees. Three very small sized (1 mm) psocids, or bark lice, were found under loose pieces of bark, one species at the 60 m (200 ft) level, a second species throughout the top half of the tree, and a third species was found only in the top three meters of the elevator study trees. These insects are scavengers in the food chain. Another small (1 to 2 mm) insect, a species of thrips, was found only in the very top of study trees and was frequently encountered while sweeping crown foliage.
Phloeosinus punctatus (Scolytidae), known in previous literature on giant sequoia as P. rubicunculus, was known only from this host, and as attacking only downed limbs (DeLeon 1952). Wood (1971) considered rubicundulus a synonym of punctatus. Dead limbs in the Castro Tree at 74 meters (243 ft) to 82 meters (270 ft) had emergence holes of this bark beetle. Adults were also collected during July in traps and by sweeping foliage.
Springtails, Entomobria sp. (Entomobryidae), were common in fissures in the bark throughout entire mature trees. Up to 22 individuals per brown cone were recorded at the 8.2 m (278 ft) level of the Castro Tree in 1967. These small, 2 mm long insects are scavengers.
Trachykele opulenta was found in the top 6 m (20 ft) of an 18 m (60 ft) giant sequoia near Redwood Saddle (at Barton's Post Camp). These beetles were responsible for the dieback of the terminal to this point. Emergence holes of this species were common in bark that was at least 10 cm (4 in) thick on more mature trees. DeLeon (1952) states that this species can complete its growth stages entirely within the bark. Many observations during this study agree with that statement.
Several important predators and parasites were found during the study. Enoclerus shaefferi, E. lecontei and Cymatodera sobara (all Cleridae) were first observed searching smaller limbs in the upper foliated portion of the Albina Tree in 1967. Their predaceous larvae were later found associated with Phymatodes nitidus in cones and small limbs. A lady beetle, Olla abdominalis (Coccinellidae), was first found in the Albina Tree and later observed in the Castro Tree feeding upon the sequoia aphid, Masonaphis morrisoni. A small predaceous beetle, Nemozoma fssiceps (Ostomatidae), was recorded in small numbers from 12 to 50 mm (1/2 to 2 in) diameter limbs that had fallen from a mature sequoia in North Area.
Larval stages of Syrphus sp. (Syrphidae) were observed actively feeding upon the sequoia aphid, Masonaphis, the latter of which was estimated to exceed over 100,000 individuals per tree (up to 10 or more per 25 mm [1 in] of new growth). The search and seizure rate of these blind predaceous maggots was one aphid in three minutes. They were noted feeding as late as 1:00 a.m, in the Castro Tree. Adult Syrphus expressed territorial behavior along the margins of foliage of the study trees. Syrphus was preyed upon by a robber fly, Neoitamus affinis, that waited in ambush and would capture Syrphus in flight. Syrphus was also parasitized in the larval stage by ichneumonid and braconid wasps.
Bee flies, Villa alternata (Bombyliidae), practiced the same territorial flight behavior as Syrphus. As many as one hundred adults were estimated to be flying about the crown of the Castro Tree during the day. The larvae of these flies are parasitic in the immature stages of Lepidoptera, Coleoptera and Hymenoptera. However, none were reared from these hosts during the study.
Large flesh flies, Sarcophaga sp. (Sarcophagidae), were observed very commonly sunning themselves on the larger limbs of the trees studied.
A leaf mining fly, Minettia flaveola (Lauzaniidae), was extremely numerous in sweep samples of foliage, at times making up to 35% of the sample. No relationship between this fly and a host was established.
Carpenter ants, Camponotus minor (Formicidae), were well established in the base of the Castro Tree, being very active at night, with limited activity the first 90 minutes after sunrise. Little attention was placed in this study on the carpenter ant, which was at time of our investigations being extensively studied by the University of California team of Drs. David Wood and Charles David. Their investigations are concerned with possible buildup of this ant in fire suppression and high park visitor areas, and the ecological role of this ant in the sequoia forest (Kilgore pers. comm.). Another ant, Leptothora muscorum, was very active on the surface of the bark during the daylight hours between 21 m (70 ft) and 80 m (265 ft) level. There are no arboreal ants known to the Sierra prior to this observation (Pitman pers. comm.).
The insect fauna of the giant sequoia is small when compared to that of other conifers of the same region. It differs considerably from that treated by Southwood (1961) in the hypothesis that insect species associated with a tree are a reflection of the cumulative abundance of that tree throughout recent geological history. Insect faunas of historically newer trees are considerably larger than those of the much older giant sequoia. The insect faunas of pines and firs are usually two to three times greater than the presently known fauna from the giant sequoia.
The physical size of most of the individual insects associated with sequoia is also small. Most insects associated with adjacent conifers are likely to be twice the physical dimensions of those of the giant sequoia. There is also a preponderance of foliage-colored insects within this fauna, making them all the more indistinguishable.
In general, fluid-feeding insects with sucking mouth parts were concentrated in the lower half of the foliated portion of the trees studied, while those with chewing mouth parts were found throughout the trees with concentration in the upper third. This may be explained by water stress problems in the tops of mature trees (Tobiessen et al. 1970), where less fluid means less pitch and resins (Graham 1952), which may allow chewing (boring) insects freedom from "pitch-out". At the same time, good fluid availability such as is the case in the lower limbs, might possibly explain the greater density of fluid feeding aphids and other homopterous insects in the bottom half of the study trees. It is the fluid pressure within the vascular tissue that forces carbohydrate-laden fluid into these insects (Chapman 1969). They do not really work for their meals.
Tobiessen et al. (1970) measured the xylem pressure potential in the Castro Tree every 15 meters along this tree's height with a pressure bomb. The measured gradient was about -0.8 bar per 10 meters height, or less than the hydrostatic gradient. Maximum water stress at the top of this sequoia approached -20 bars, which may explain the abundance of fluid feeding insects in the lower portion of the study trees.
Of the 143 species of insects encountered in this study, 4 species were found on seedlings (3 of these were also in older trees). Thirty-two insects were found in different stages of downed and dead limbs of standing giant sequoias, while 3 of these were also observed in standing dead wood of the living host. One hundred and fourteen insect species were found only in the canopy of the living tree.
The small fauna of the giant sequoia also has a small interaction, i.e. food webs. The majority of the insects are small and pigmented similar to the sequoia bark or foliage and display very little interspecific activity such as shown in the food web of Masonaphis and Syriphusichneumonid and braconid parasitesNeoitamus and Villa.
In summary, the giant sequoia, the largest living organism past or present, and one of the oldest, is unusual in having relatively small insects comprising a relatively small insect fauna.
Last Updated: 06-Mar-2007