Ips grandicollis
(five-spined bark beetle)

I. grandicollis is known from the USA and Canada since 1868. As well as those states listed (see Distribution List), I. grandicollis is probably present in Delaware, Kentucky and Vermont because these states contain suitable hosts and are surrounded by states where I. grandicollis is known to occur.

More recently discovered in more southerly locations, such as Central America, Caribbean Islands and Mexico (Garraway, 1986; Berrios et al., 1987; Guerra et al., 1989; Haack and Paiz-Schwartz, 1997) but it is not known whether I. grandicollis is native to these regions or introduced. I. grandicollis was introduced to Australia in the 1940s, where it is now widespread and common throughout forests that contain Pinus (Rimes, 1959; Morgan and Griffith, 1989; Abbott, 1993).

I. grandicollis is an A1 quarantine pest for EPPO. As I. grandicollis can make primary attacks on Pinus spp., it does present a risk to the EPPO region, where Pinus spp. are important forest trees. This risk is regarded as relatively moderate. However, following its introduction into Australia, I. grandicollis has damaged Pinus pinaster and P. radiata, which are also widely planted in the EPPO region (EPPO/CABI, 1997).

Indigenous Ips spp. already occur on conifers throughout most of the EPPO region, so the risk arising from introduced species is uncertain (EPPO/CABI, 1997).

I. grandicollis is found beneath the bark of dead and dying trees, feeding and reproducing in the phloem of nearly all species of Pinus within its geographical range.

Adult males locate potential host material through a process that is not well understood. Nearly all recently dead host material gets colonized; lightning strikes and windthrown trees are usually found and colonized, as is most logging debris. However, living and apparently healthy trees can also be attacked. Unlike most of its congeners, I. grandicollis is clearly attracted to host volatiles, which presumably contributes to host location. Once a tree has been chosen, the male bores through the bark and excavates a nuptial chamber in the phloem layer, while emitting in his frass the aggregation pheromone ipsenol (Renwick and Vite, 1972). Ipsenol attracts mates, as well as other males who initiate their own galleries. Females enter a nuptial chamber, mate, and excavate egg galleries branching from the nuptial chamber. I. grandicollis is polygamous, and the original nuptial chamber built by the male may become the centre of a 'Y' or 'H' shape, as two to four females (occasionally more) each excavate their own egg gallery from the common nuptial chamber. The male typically remains in his nuptial chamber throughout oviposition, where he repeatedly mates with the females and assists in removing frass from the system of phloem tunnels.

Females lay up to 50 eggs, each in an individual niche cut into the phloem tissue of the oviposition gallery wall. Niches are individually covered by the female with plugs of chewed phloem. Eggs hatch after 3-5 days, and larvae begin mining their individual feeding galleries at right angles to the egg gallery. They pass through three larval instars, each lasting several days. Pupation lasts another 3-5 days, after which the callow adults spend another 1 or 2 days within the pupal chamber; during this time the colour of the adult changes from a very pale tan to a dark or reddish brown. A period of pre-maturation feeding begins where the adult meanders through the host material phloem, feeding as it goes, for a period of up to several weeks, depending upon the geographic location and season. After this period, the sexually mature adult emerges by chewing a small, round exit hole out through the bark.

In a trial in west-central Wisconsin under natural summer temperatures (average daily mean, maximum, minimum air temperatures during the period = 19.4, 36.6, 0.2°C, respectively) the median development time for a population in a log, from attack to emergence, was 76 days (Ayres et al., 2001). The development process is highly temperature dependent, however, so this can be expected to vary widely. In the southern USA, where I. grandicollis is multivoltine, emerging adults immediately begin flights in search of a suitable host. In the north-central USA, where it is univoltine, emerging adults either go directly to an overwintering site in the forest litter layer, or to a temporary feeding site. Spring emergence from overwintering sites is apparently cued by rising soil and air temperatures in the spring. In Wisconsin, first flights typically occur when soil temperatures rise above 5°C and air temperatures exceed 15°C. The lower lethal temperature for adults is -12 to -18°C depending upon genotype and season (Lombardero et al., 2000). All immature life stages are extremely vulnerable to winter mortality, both because they tend to be less cold tolerant and because they remain within the phloem of host trees where they seldom benefit from insulation by snow (Lawson, 1993; Lombardero et al., 2000).

Within its native forests of North America, I. grandicollis forms part of a large community that co-occurs and interacts within the phloem layer of dead and dying trees (Riley and Goyer, 1988). These diverse assemblages usually include other bark beetles, several groups of insect predators and parasitoids (see Notes on Natural Enemies), numerous species of mites and fungi (commonly phoretic on adult bark beetles), wood boring insects (especially Cerambycidae and Buprestidae) and many other species that are fungivores, scavengers, or generalist predators. Major outbreaks of I. grandicollis seem to be less common within its native forests than in Australia, perhaps because population fluctuations within the rich native community are dampened by species interactions. However, pestilence in native forests may sometimes be exacerbated when I. grandicollis is able to co-operate with congeners in mass attacks of host trees (Ayres et al., 2001) or benefit from outbreaks by more aggressive bark beetles such as Dendroctonus frontalis.

In the USA, I. grandicollis has a plethora of natural enemies, primarily arthropod predators and parasitoids. The adults of several species of Cleridae prey on adult I. grandicollis during their initial colonization of host trees, and clerid larvae prey on I. grandicollis larvae during subsequent brood development within host trees. Of these, Thanasimus dubius is the most abundant and widespread. In the southern USA, T. dubius tends to be supplanted as a predator of I. grandicollis by Temnochila virescens [Temnoscheila virescens] (Trogossitidae). Several species of Histeridae, e.g. Platysoma cylindricum, are also abundant and, presumably important, predators of I. grandicollis. Dipterans, of which Medetera bistriata (Dolichopodidae) may be most significant, are voracious predators in their larval stage, prowling the bark beetle galleries feeding on larval and pupal stages. Parasitic wasps such as Roptrocerus xylophagorum (Pteromalidae) parasitize bark beetle larvae by ovipositing through the outer bark into larval feeding galleries.

Although predators and parasites have demonstrated demographic importance in controlled experiments (Riley and Goyer, 1986) and are presumably significant forces in natural populations, only one species has been found to be an effective biological control agent. Whilst Thanasimus dubius, Temnoscheila virescens and R. xylophagorum have been introduced into Australia, only R. xylophagorum has established and impacted upon I. grandicollis. R. xylophagorum is now widespread in Australia and can achieve up to 70% parasitism (Waterhouse and Sands, 2001).

Local presence of I. grandicollis can be monitored using funnel traps baited with the male aggregation pheromone ipsenol. However, since this species maintains an endemic presence in most pine forests within its range, its presence does not presage imminent outbreak.

I. grandicollis is similar in size, colour and shape to many species of bark beetles. In adults, the deeply scooped out declivity bordered by five pairs of spines, the hidden head and the flattened, imperfectly round antennal club distinguish it from all bark beetles except for a few other species of five-spined Ips, from which it cannot easily be distinguished except by host, geographical range, or genitalia. The other life stages are virtually impossible to differentiate from many other phloem-feeding bark beetles.

Damage to trees by I. grandicollis is very similar to damage caused by other bark beetles, especially other members of the tribe Ipini. I. grandicollis often coexists with other bark beetles within the same phloem tissues of the same tree.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Introduction

In the forests of the USA, I. grandicollis is considered the least aggressive of the bark beetle species that it co-occurs with; therefore, control measures are rarely focused on it. Within that community, it cannot be ascertained whether I. grandicollis would cause more damage in the absence of other bark beetles, or less, and in fact such a question may be irrelevant in the context of pest control. In other regions of the world, especially where it is an exotic, control measures may be more necessary, more effective, and more justifiable.

As with most pests, control of I. grandicollis is comprised of three strategies: monitoring, prevention and suppression. Control goals may be to either prevent tree mortality or to reduce blue stain damage (I. grandicollis is a vector for blue stain fungi), or both; and although similar strategies may be employed toward both goals, they may differ.

Field Monitoring

Several pheromone trap designs have been tested (Rose et al., 1981; McCravy et al., 2000) and shown to be effective for monitoring population size when baited with the aggregation pheromone ipsenol. Aerial forest surveys can readily detect and help quantify outbreaks and attacks. Such monitoring can help determine the need for suppression tactics. It is probable that the response threshold will differ depending on the situation and size and nature of the damage, but in many cases it may be the same as a natural response threshold that theoretically corresponds to the escape threshold in multiple equilibria models of population dynamics (Berryman, 1987). In the case of blue stain prevention, it may be easier and more effective to focus efforts on reducing the process time of infected material rather than to try to prevent infection.

Cultural Control and Sanitary Methods

There are several prevention tactics that may reduce the likelihood of insect populations reaching a crucial threshold. Harvesting practices like slash sanitation during logging, prompt movement of logs from logging sites, and prompt salvage logging after natural disasters like fires and windstorms may help prevent population growth to dangerous levels. Silvicultural practices that reduce or avoid large acreages of overstocked mono-specific stands of susceptible hosts can help, as can management plans that help maintain healthy populations of natural enemies.

Some of the same tactics for prevention can be used for suppression. Removal of infected logs in infested forest areas, salvage logging and debarking or processing of infested logs can reduce populations and minimize both unintended tree mortality and blue stain damage to logs both in the forest and in the mill yard, especially if done promptly.

Mass trapping with the same traps and lures used for monitor trapping can be effective at capturing large numbers of insects; and multiple equilibria models (Berryman, 1987) suggest that it may be possible to suppress populations below the escape threshold. Success has not been demonstrated, however, and whether such mass trapping campaigns decrease populations enough to reduce damage remains arguable.

Chemical Control

Many synthesized and naturally occurring chemical substances have been tested for use as possible prevention and suppression tactics. One strategy involves using semiochemical disruption of the aggregation process. Certain green leaf volatiles (Dickens et al., 1992), 4-allylanisole (Hayes et al., 1996), verbenone, pine oil (Berisford et al., 1986; Nord et al., 1990) and a wide range of odoriferous compounds (All and Anderson, 1974) have been tested. Of these, a few showed some potential (verbenone, green leaf volatiles, ammonium hydroxide and 4-allylanisole), but none have become cost-effective solutions.

Many other chemicals have been tested as insecticides, such as carbaryl, chlorpyrifos-methyl, deltamethrin and propoxur (Ragenovich and Coster, 1974; Stone and Simpson, 1987). Fuel oil mixtures have been shown to cause high I. grandicollis mortality when applied on logs (Cibulsky and Hyche, 1974). Of these, only carbaryl, under the trade name Sevimol, is currently labelled for use in the USA, along with permethrin (trade name Astro) for control of bark beetles. There is also a pending registration for bark beetle control for bifenthrin (trade name Onyx).

It must be noted that both insecticides and deterrents have limited utility due to the cost of application and degree and duration of protection, and have never been shown to be effective in the forest setting. Additionally, they may have side effects that may outweigh possible benefits. They may, however, have limited use in protecting individual high value trees, or for temporary protection against log deck degradation.

Biological Control

Many potential candidates have been evaluated for use as biological control agents in Australia (Berisford, 1989). Neither of the introduced predators, Temnoscheila virescens and Thanasimus dubius, are known to be established, but two parasitoids have established. Of these, only Rhoptocerus xylophagorum has had any impact. R. xylophagorum is now widespread and causes up to 70% parasitism. This attack, combined with much improved silvicultural management (including removal of bark from slash and logs), has greatly reduced the damage caused by I. grandicollis (Waterhouse and Sands, 2001).