Chapter 8: Beneficial organisms
Many species appear to be potential threats for commercial success in forestry. On the other hand, many others are neutral, or even beneficial from point of view of forest protection. The most beneficial organisms in forest protection appear to be fungi and animals – particularly insect predators and parasitoids and predatory birds.
Beneficial organisms could be divided into those that are causing decline in population densities of pests, weeds etc. For example, this is the case of parasitic (parasites and parasitoids) and predatory taxa that forage insects, which causing damages to the forests. The same beneficial effect could have fungal pathogens of insects and weeds and last but not least hunters and their impact on game stocks. Of course, in this case is the term beneficial organism a bit inappropriate. The others are those that help to the forest protection in some particular cases – like saproxylic insects and fungi that are competitors of potential pest. They causing decay of stumps that are habitats for some potential pests – like large Pine Weevil (Hylobius abietis).
It is well known that birds and namely woodpeckers are predators of bark beetles and the same effect have other birds on phytophagous insects – especially on caterpillars. Nevertheless, bird predators are rather taxon (or species) unspecific – i.e. they are generalist predators. The same case is ground beetles (Carabidae), many species are more or less specialized but they are able to forage on more taxa. For instance, adults of genus Calosoma known as caterpillar hunters appears to have the population density level highly interconnected with lepidopteran defoliators. As mentioned above, hunters are one of the ways how to reduce high game stocks. Nevertheless, in ecosystems that are more natural or semi-natural (like boreal parts of Asia and North America) there can be seen high impact of large predators (wolves, lynxes, bears) – some of which are more (lynx) or less (bear) prey specialized. Generalist predators are more efficient in endophytic predation, while more specialized ones are exophytic predators (e.g. under the bark of a tree).
Specialized predators and parasitoids are one of the most beneficial organisms in forest protection. Population densities of their prey do not need to be the only one factor that influenced predators and parasitoids and thus it is often studied what are the other factors that influencing their population densities. One of the examples could be clerid beetle Dermestoides sanguinicollis, which is a predator specialized on wood worm beetles (Anobiidae) on oaks. This clerid beetle is, in conditions of central Europe, associated with sun-exposed trees and thus its foraging success on wood worms greatly decrease toward oaks in dense forests.
Both predators and parasitoids are mostly dependent on chemical communication and three main components are mentioned by authors – (i) communication within the same species (intraspecies), (ii) recognition of odours of trees damaged, weakened or even inhabited by prey and finally (iii) hacking of communication done within its prey. The most efficient and successful predators are able to communicate on more levels. Unfortunately, this may lead to very high specialization and thus these species need to be highly synchronized with prey. Example is clerid beetles (Cleridae) like Thanasimus dubius, whose adults are arriving on host tree before its prey (use of hacking of communication of its prey). They are also mentioned that they are able to smell the odour of damaged trees – nearly in the same way as in olfactory system of their prey. When prey is arriving and start to dwell into the bark, predatory clerids are calling the others (intraspecific communication) that quickly arrive and kill bark beetles (exophytic predation). They mate and oviposit close to the entrance holes of bark beetles. Their larvae are foraging on larvae of bark beetles under the bark (endophytic predation)
In the case of predators is also questionable if the species is obligate (like Cleridae), facultative predator (like some click beetles (Elateridae) larvae are predators, while adults not) or opportunistic predators (like flat bark beetles (Cucujidae)). Very good example is forest ants (Formicidae). Some species are extremely greedy predators (some Formica species) that are able to clear the forest stand from other arthropods. Nevertheless, many other ant species are only facultative predators or opportunists. Even some of them, which have high body volume, which enabled them to prey on arthropods – This is the case of Carpenter ants (Camponotus spp.). They are foragers that typically eat parts of other dead insects or substances derived from other insects – like in some ant species that lick substances on aphids. Beetles, ants and birds are most probably the most efficient predators. Although, there are many others that are of importance – e.g. small mammals like some shrews (Soricidae), reptiles like lizards (Lacertidae), several flies (Diptera), wasps (Hymenoptera), bugs (Heteroptera), snakeflies (Raphidioptera) or dragonflies (Odonata).
Traditionally, parasites and parasitoids are referred primarily to organisms visible to the naked eye – so called macroparasites (not only insects, but e.g. helminthes or protozoans). Nevertheless, here are also many other microparasites like viruses and bacteria, which impact on pests and weeds could be high. Although, the present stage of knowledge is still rather low. An example could be fungi Beaveria bassiana (Clavicipitaceae), some of which strains are insect pathogens. The research on these fungi is in progress and this fungus was more or less successfully used against bark beetles or bugs. Contrary to Beaveria bassiana, relatively well known is bacteria Bacilllus thuringiensis. Some of its strains are recently used in forest protection and it is also well known as a part of Bt-economic plants. This bacteria has been often used against insect defoliators – like Gypsy moth (Lymantria dispar), which was introduced into North America in 1869 from Europe.
In some cases it is hard to distinguish if it is parasitism or if better name is disease, pathogenity etc. Parasitism (at least the visible part of this process) is mostly restricted to the insects and hymenopterans and dipterans are probably the most efficient ones. Highly visible are also so called hemiparasites like mistletoes (Viscum and Loranthus) that are mostly interconnected with mature and overmature trees. Same as in predation on insects, parasitism starts on eggs and finishes on adults. There are known several species of trichogrammatid wasps (Trichogramma) that parasitize on eggs of bark beetles. Eulophid chalcid wasps like Entedon species are ovipositing into eggs and early instars of larvae of their prey. Pteromalid chalcid wasp Rhopalicus tutela is ectoparasitoid of larvae. There are also several species that are endoparasitoids of adults –like another pteromalid Tomicobia seitneri. Parasitoids seem to be rather species or taxa specific, while the errors in literature do not make final conclusions for species specificity so easy. One example of the species with rather nonspecific hosts is pteromalid wasp Dendrosoter middendorfi.
Last but not least group of beneficial organisms are dead wood dependent (saproxylic) organisms. If we exclude those that are potential pests and pathogens, we may find that there are many taxa that are potentially beneficial for forest ecosystems. Probably the most important saproxylic taxa are beetles (Coleoptera) and fungi. The others are Hymenoptera, lichens (lichenized fungi) and bryophytes (e.g. mosses). The present agenda on the research on saproxylic organisms indicate that they are beneficial and their impact is the most important in highly spatially (both horizontally and vertically) diversified environments.
Fig. 8.1. Female of parasitic ichneumonid wasp Dolichomitus mesocentrus laying their eggs into some larva (probably longhorn) under the bark of the Black Alder (Alnus glutinosa).
Example 8.1: Aukema B.H., Raffa K.F. (2002) Relative effects of exophytic predation, endophytic predation, and intraspecific competition on a subcortical herbivore: consequences to the reproduction of Ips pini and Thanasimus dubius. Oecologia 133: 483-491.
As the abiotic disturbances and insect outbreaks appear to be more frequent in present years, the role of specialized predators on bark beetles is still much more studied. Pine Engraver Beetle (Ips pini) is a bark beetle native to North America. It kills weak and damaged trees of small diameters, although when reach high population densities its damages might become more important especially in pine plantation forests. Thanasimus dubius is a predatory clerid beetle specialized on bark beetles. Its adults are arriving before or with bark beetle adults and kill them immediately. Females of this clerid beetle are laying their eggs nearby the entrance holes of bark beetles and clerid larvae start with the predation inside of the galleries.
Aukema & Raffa (2002) studied the effect of exophytic and predation of Thanasimus dubius on Pine Engraver Beetle. They found that clerid adults and larvae can efficiently reduce the densities of Ips pini. Higher number of individuals of predators decreased the progeny and males of prey. However, when clerid adults increased the abundance on bark surface then the predation per adult decreased. Predation of larvae and adults of clerids on bark beetle was nearly the same, although adults ate nearly 20 times more prey than larvae.
Example 8.2: Edworthy A.B., Drever M.C., Martin K. (2011) Woodpeckers increase in abundance but maintain fecundity in response to an outbreak of mountain pine bark beetles. Forest Ecology and Management 261: 203-210.
Birds and especially woodpeckers are known as predators of bark beetles. They are mostly high efficient predators on insects that are able to foraged even on prey inside the tree trunks. They are known to increase their abundances in the places where some forest disturbance occur and high densities of insect prey are presented. Although, their predation abilities are well known, there is question if they are also able to increase their fecundity during the time when food supply is increasing.
Edworthy et al. (2011) studied the fauna of temperate woodpeckers in British Columbia (U.S.A.) and relationship to the increasing number of prey after the mountain bark beetle (Dendroctonus ponderosae) outbreak. They have studied this problematic for 15 years. Six species of woodpeckers were evaluated: downy woodpecker (Picoides pubescens), hairy woodpecker (Picoides villosus), American three-toed woodpecker (Picoides dorsalis), pileated woodpecker (Drycopus pileatus), northern flicker (Colaptes auratus), and red-naped sapsucker (Sphyrapicus nuchalis). The number of individuals of woodpeckers increased during the years of bark beetle outbreaks. Even if, it is known that woodpeckers are relatively conservative in their fecundity, it was relatively surprising that despite the year-round multi-annual increase in food resources their annual fecundity was not increased – even when most of other bird species strongly increased their fecundity.
Example 8.3: Pettersson E.M., Birgersson G., Witzgall P. (2001) Synthetic attractants for the bark beetle parasitoid Coeloides bostrichorum Giraud (Hymenoptera: Braconidae). Naturwissenschaften 88: 88-91.
Parasitoids of potential pests are known to be efficient biological control. Ectoparasitoid wasp (Coeloides bostrichorum) is a parasitic species of late instars of coniferous bark beetle larvae and especially two most important spruce bark beetles in Europe – Spruce bark beetle (Ips typographus) and six-toothed bark beetle (Pityogenes chalcographus) – are its main hosts. It is known that this parasitoid species appears to be specialized. This species could be relatively abundant, although its ecology was poorly understood.
Pettersson et al. (2001) studied the host searching strategy of adults of Coeloides bostrichorum under the laboratory conditions. They found that oxygenated monoterpens were typical for bark beetle damaged trees, while monoterpene hydrocarbons were more typical for healthy trees of the Norway spruce (Picea abies). Parasitoid wasp was the most attracted by odours from spruce logs that contained late instar larvae of bark beetles. However, when fresh logs uninfested by bark beetles were baited by combination of suitable odours, adults of Coeloides bostrichorum were arriving on them. This reflected the situation that most predatory and parasitic taxa are highly dependent on chemical communication – and especially hacking of prey communication is one of the most important.
Example 8.4: Prikryl Z.B., Turcani M., Horak J. (2012) Sharing the same space: foraging behaviour of saproxylic beetles in relation to dietary components of morphologically similar larvae. Ecological Entomology 37: 117-123.
The larvae of flat bark beetles (Cucujidae) and fire colored beetles (Pyrochroidae) are often mentioned as predators of species living under the bark of trees, including bark beetles and other potential pests. The European flat bark beetle (Cucujus cinnaberinus) is red-listed by IUCN, while two fires colored beetles Schizotus pectinicornis and Pyrochroa coccinea are relatively common in central Europe. Mostly based on observations, authors often mentioned that their extremely flat bodies and environment predicted them to foraging on other insects. Nevertheless, observations of other beetle taxa associated with the microhabitats of flat bark beetles and fire colored beetles are only scarce.
Prikryl et al. (2012) studied larvae of these three potentially predatory taxa in the wild during more years. There were few signiﬁcant differences in diet among the study species, but there were signiﬁcant differences for the different dietary components in individual species. Guts of all three species included more plant and fungal material than animal. On the other hand, they observed signiﬁcant differences among species and selection with respect to body size during the overwintering period – larvae swallowed more animal and less fungal material with increasing body size. The species seem to be only opportunistic foragers, varying their foraging capability according to seasonality and age. They probably generally foraged woody material infested by ﬁlamentous fungi (i.e. xylomycetophagy).
Example 8.5: Horak J., Vodka S., Kout J., Halda J.P., Bogusch P., Pech P. (2014) Biodiversity of most dead wood-dependent organisms in thermophilic temperate oak woodlands thrives on diversity of open landscape structures. Forest Ecology and Management 315: 80-85.
Dead wood dependent organisms are often known as saproxylics. These species are dependent at least in some part of their life on dead wood. Saproxylic organisms are decomposing the woody material that was left in forest and thus they are beneficial in forest protection – e.g. they forage inside the stumps, where compete with potential pests. On the other hand, many of potential pests are indexed also as saproxylics – like bark beetles. The most studied and well known taxa are beetles and fungi. Nevertheless, studies on comparison of more taxa were lacking.
Horak et al. (2014) studied four saproxylic taxa – beetles (Coleoptera), Aculeata Hymenoptera , fungi and lichens (i.e. lichenized fungi) in the woodland area of thermophilic deciduous woodland in the Czech Republic. They found that saproxylic organisms are the most positively influenced by rising diversity and openness in disparate landscape structures. Solitary trees, natural forest edges and sparse forest stands hosted higher biodiversity than closed canopy stands. Only fungi were not responding to studied landscape patches. Thus, most saproxylic organisms preferred high spatial heterogeneity of mature stands. Traditional forest management like wood pasturing, coppicing or its simulation like game keeping appears to be one solution to mitigate biodiversity loss.
Fig. 8.2. Larva of some predatory clerid beetle (probably Thanasimus formicarius). Larvae of most clerids forage endophyticly on insects living under the bark, while adults are exophytic foragers on adults of bark beetles arriving on bark surface of attacked trees.
Questions for exam:
8.1. Clerid beetles are one of the most efficient predators of bark beetles. Both adults and larvae prey on all life stages of bark beetles. The predation of larvae of clerid Thanasimus dubius takes place:
8.2. There are many bird species that prey on potential forest pests. Several of them are more specialized than the others – e.g. on caterpillars or on bark beetles. What are the most efficient bird predators specialized on bark beetles?:
8.3. Parasitoids kill their host, while parasites not. Although, parasites mostly caused damages to their inner organs – for example bark beetles are not able to reproduce after parasitism of Tomicobia seitneri. Adults of parasitoids mostly lay their eggs inside the body of their prey. What are one of the most important endophytic (i.e. under the bark) parasitoid taxa that forage on bark beetles?
8.4. Forests are home for myriads of organisms. Many of them are beneficial, because they help to decompose the woody debris after the timber harvest. What is the name for beneficial organisms that help to decay the woody residuals?: