0417-B3

Damage Status of Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae) and Effectiveness of Rhizophagus grandis Gyllenhal (Coleoptera: Rhizophagidae) On It In The Field

Hazan ALKAN AKINCI, Gonca Ece ÖZCAN, Mahmut EROĞLU ¹

Abstract

In this study spruce forests were studied in Artvin, Giresun and Trabzon districts to determine damage status of Dendroctonus micans (Kugelann) (Coleoptera: Scolytidae) and effectiveness of Rhizophagus grandis Gyllenhal (Coleoptera: Rhizophagidae) on it. In 33 plots, a total of 1186 trees were evaluated. D. micans damage was determined on 195 trees (28%) of the studied trees present on all plots. It's determined that the damage continues to last on 84 trees (12%), and the damage continues and on 111 trees (16%) D. micans damage had already taken place before the study was conducted. It was observed that D. micans damage was still continuing 43% of the harmed trees.

The damage was found to have occurred before the study on 48 (48%) of the 101 (%14) injured trees and still continues on 38 trees (38%). Eighty-six trees (44%) out of 195 trees damaged by D. micans, and 38 trees (45%) out of 84 trees on which D. micans was still active were wounded trees.

In the studied plots, a total of 4548 entry and exit holes were counted on 191 trees. Fifty one percent of the entry and exit holes, an indicator of the active D. micans individuals density were counted on the bole of the trees from ground level up to 1 m high.

R. grandis, the spesific predator of D. micans, were determined in 22 D. micans galleries on 18 trees in 14 plots. In these galleries, a total of 384 R. grandis and 997 D. micans were counted in different biological stages. The effectiveness of R. grandis on D. micans in plots was 84%. The effectiveness was %29, when the galleries with and without R. grandis were evaluated together in plots. When D. micans quantity in whole plots was evaluated, the general effectiveness of the predator is 15%.

Introduction

The genus Dendroctonus Erichson (Scolytidae) has over 20 species worldwide. Most of these occur on conifers in North and Central America, where they are the most destructive natural biological factors. D. micans, the greater Europian spruce bark beetle, is the principal Eurasian representative of the genus. The only other Eurasian species is Dendroctonus armandi Tsai&Li, a Chinese species (Grégoire 1988; Lempérière 1994; Fieldig and Evans 1997).

The adult D. micans exhibits several life cycle characteristics that are atypical of most other scolylid species. Mating takes place under bark, prior to emergence and before the adult beetles are fully chitinized, the females normally being fertilized by sibling males. This explains the low number of males (typically one to every 10 females, but as low as one to 45) found in this species (Grégoire 1983; Grégoire 1988; Fieldig and Evans 1997). Emergence can take place over a protracted period with many beetles using one mergence hole (Fieldig and Evans 1997). Once suitable host material is located, the female bores through the bark to reach the cambium layer where she attempts to establish a brood chamber and subsequently to oviposit, clearing resin, the tree's first line of defence, which accumulates in the chamber. (Fieldig and Evans 1997). Newly hatched larvae present a rather uncommon feature among bark beetles: they spent almost whole larval life in a collective intra-cortical brood chamber (Grégoire et al. 1982). There are 5 larval instars. Mature larvae move back into the fresh `islands' behind the feeding front where they construct single pupal chambers (King and Fielding 1989; Fieldig and Evans 1997). The young callow adults gradually darken and they can remain under the bark for long periods or over winter there (Lempérière 1994). D. micans life cycle is remarkably adopted to a wide variety of climatic conditions and any stage of the insect may be found throughout the year. The duration of its life cycle vary greatly. Observations show a short cycle with almost one generation per year, and a slower life cycle with one generation every 2 or 3 years (Lempérière 1994).

It's known that D. micans, first determined in Turkey in 1966 is found in around 250 000 ha of 445 000 ha (oriental spruce) Picea orientalis (L.) Link. forest and continues to extend its spread.

Invading Turkey from Georgia, D. micans has become an important pest of P. orientalis and spread quickly over large areas of Artvin, Giresun and Trabzon districts. Detection surveys for D. micans conducted mainly in the forests at Artvin Region from 1992 to 1995 showed that about 36 % of the trees was infested by this pest. The pest was active in 25 % of all trees. In addition, the intensity of the infestation was very high in the front lines in particular infested trees in some new infested stands (Eroğlu 1995).

R. grandis is the single most important and potentially useful natural enemy of D. micans throughout its Eurasian range. The first notable artificial breeding and release of this predator began in 1963 in the Georgian Republic, and is still on going, being regarded as influential in reducing serious outbreaks of D. micans in the extensive oriental spruce forest (Kobakhidze et al. 1970). A similar programme began in France and England in 1983 (Grégoire et al. 1984a; Fieldig and Evans 1997) and in Turkey in 1984 and still on going (Keskinalemdar et al. 1986; Alkan and Aksu 1990).

The life cycle of R. grandis can be clearly divided into two phases: firstly the underbark establishment and feeding stages of the larvae, culminating in the migration of prepupae from tree to soil; and secondly the prepupal, pupal and adult development stages in the soil (King et al. 1991). About 45 days are spent from the prepupal stage to the emergence of young adults. Male adults emerge slightly before the females. This could favor early kin mating thus allowing the females to colonize a prey system as rapidly as possible (Merlin et al. 1984).

R. grandis was introduced for the first time in Georgia since 1963 and now play an important part there in the regulation of D. micans populations. Based upon these claims, a vast biological control program has been developed in Artvin and Giresun districts since 1985 and more recently in Trabzon district in Turkey. D. micans and R. grandis have been present in these districts for such time that allowed us to study some relationships between both species under epidemic conditions. Field surveys were conducted in 2001 and 2002.

Material and Method

The results of the study were based on the detections in 14 experimental plots with 479 trees were both D. micans and R. grandis were found together and in 19 plots with 707 trees where only was D. micans present.

On each plot, diameter of breast height (dbh) were measured, the pitch tubes on boles and exit holes in tree bark were counted. The bark on the attacked parts of the stems was carefully stripped and the eggs, larvae, pupae and adults of D. micans and R. grandis were counted. Number of abortive entrance holes, position of pitch tubes on trees and area of old or newly constructed brood systems were recorded. Number of both species counted in each prey's brood system was given in Table 1. The relationship between both species was evaluated comparing the densities of D. micans and R. grandis.

The effectiveness of R. grandis on D. micans were evaluated together when the galleries with and without R. grandis in plots.

Results and Discussion

D. micans was found in all plots. Twenty-eight percent of the trees were infested by D. micans and the damage of the beetle was continuing in 12 % of the trees. 540 adult beetles were counted in 58 trees. Sixty-five percent of the adults were found on 2 plots and 96 % of them were counted in only five trees. Average beetle number per tree in these 2 plots was 63 and only 4 on the other plots.

At the time of investigation, 75 female beetles were boring through the bark, 21 females were opening egg galleries, 19 females were ovipositing and 42 females were with first and second instar larvae in galleries.

In 20 plots a total of 2905 D. micans larvae were counted on 41 trees. Four of these 20 plots included 57 % of the total number of larvae of D. micans. The average number of larvae per tree was 165 on these 4 plots in 10 trees and, it was 40 on the other 16 plots. In 5 plots 177 pupae were counted in 7 trees. These data revealed that pest density is intensive on certain areas and trees.

Table 1. The number of D.micans and R. grandis in each prey's brood system.

Seventy-two percent of the total number of D. micans counted was on 19 plots where R. grandis was not present. Sixty-five percent of D. micans counted on these 19 plots was from 4 plots in Trabzon-Maçka Forest, D. micans was newly infested and still progressing its spread since 1998.

Twenty-eight percent of the total number of D. micans counted was on 14 plots where R. grandis was present. In these plots they were determined in 22 galleries on 18 trees. In these galleries, in different biological stages, a total of 384 R. grandis were counted with 997 D. micans. The effectiveness of R. grandis on D. micans in plots, in which they were determined together was 84 %. When R. grandis larvae and adults effectiveness in galleries calculated separately, it's seen that the effectiveness of R. grandis larvae in galleries was 79 % and effectiveness of R. grandis adults was 100 %. Then in plots that D. micans found with R. grandis, the R. grandis determined and undetermined galleries have taken into account in effectiveness calculation. In this situation the effectiveness was 29 %. The general effectiveness of the predator was 15 % when total D. micans quantity in sample plots were estimated.

D. micans damage was found to have occurred before the study on 48 % of wounded trees and still continues on 38 % of them. Fourty-four percent of 195 trees damaged by D. micans, and 45 % of 84 trees on which D. micans was still active were wounded trees.

In the whole plots, a total of 2650 entrance holes (19 % of them were abortive holes) and 1898 exit holes were counted. Of the entrance holes on the bole of trees 34 % were between 0-0.5 m, 17 % were between 0.5-1.0 m, 27 % were between 1.0-2.0 m, 15 % were 2.0-4.0 m, and 7 % were 4.0-8.0 m. From this data it's seen that 51 % of the entrance holes, which is an indicator of the active D. micans individuals density, were counted on the bole of the trees from ground level up to 1 m high. These characteristics of the pest facilitate mechanical control.

Conclusion

The survey data indicate that all spruce stands in Artvin and Giresun district and Trabzon-Maçka forests shelter D. micans.

During the survey, D. micans was still progressing its spread in Trabzon-Maçka forests. Mass-rearing and extensive releases of R. grandis might thus be needed to continue for several years.

The effectiveness of R. grandis on D. micans in plots was 84%. The effectiveness was %29, when the galleries with and without R. grandis were evaluated together in plots. When D. micans quantity in whole plots was evaluated, the general effectiveness of the predator is 15%.

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¹ Res. Assist. Pr.
Karadeniz Technical University,
Faculty of Forestry, 61080 Trabzon, Turkey
0 462 377 3496 - 0 462 377 3154
[email protected]
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