New braconid parasitoids (Hymenoptera: Braconidae) on bark beetles in Ihtimanska Sredna Gora Mountain, Bulgaria

In 2020, two braconid species (Hymenoptera: Braconidae) were found as parasitoids of bark beetles in Pinus sylvestris plantations in Ihtimanska Sredna Gora Mt. Coeloides bostrichorum Giraud was reared from stem samples attacked by Tomicus piniperda and Tomicus minor in the region of Krushovitsa vill. (State Forestry Enterprise Elin Pelin), and Dendrosoter middendorffi (Ratzeburg) – by Ips acuminatus , Pityophthorus pityographus and Pityogenes bistridentatus in the region of Krushovitsa vill. and Golema Rakovitsa vill. (State Game Enterprise Aramliets). Coeloides bostrichorum caused 7.4% mortality of T. piniperda and T. minor , and Dendrosoter middendorffi – 5.6-12.5% of Ips acuminatus , 5.6% of P. bistri-dentatus , and 2.8% of I. acuminatus , P. pityographus and P. bistridentatus . In the total braconid parasitoid complex, D. middendorffi was the dominant species with a relative share of 87.5%.

In the last sixty-seventy years, extensive anti-erosion plantations of Scots pine (Pinus sylvestris L.) and Austrian pine (Pinus nigra Arn.) have been created in the lower and middle forest belts in Bulgaria, where attacks by bark beetles have recently been observed (Mirchev et al., 2016).No investigations on scolytid parasitoids have been conducted in the attacked pine plantations, with the exception of a study that identified six species from Pteromalidae and Heydeniidae families (Hymenoptera: Chalcidoidea) in Ihtimanska Sredna Gora Mt. (Belilov et al., 2023).
The present note reports two braconid parasitoids (Hymenoptera: Braconidae) of bark beetles in pine plantations in Ihtimanska Sredna Gora Mt.

Materials and methods
The studies on parasitoids of bark beetles were conducted in 2020 in two plantations of Pinus sylvestris L. in the region of Krushovitsa vill.(State Forestry Enterprise Elin Pelin) and Golema Rakovitsa vill.(State Game Enterprise Aramliets) (Fig. 1).
The main characteristics of the studied plantations are presented in Table 1.The samples (cuttings of stems and branches of approximate length 30-35 cm and diameter 5-30 cm) of trees attacked by bark beetles were collected in June.
The biological material was transported to the Forest Research Institute in Sofia where each cutting was kept in a separate photo eclector at room temperature (18-22ºC).The samples were observed weekly for the emergence of adult hosts or parasitoids.
The emerged bark beetles were identified using the keys of Karaman (1971) and Grüne (1979), and the parasitoids -using the key of Tobias (1986).
The biological material was deposited in the entomological collections of the Forest Research Institute in Sofia.
Coeloides bostrichorum caused mortality of 7.4% of the population of T. piniperda and T. minor (Table 2).The mortality caused by D. middendorffi varied from 2.8% in the I. acuminatus, P. pityographus and P. bistridentatus population, to 12.5% in the I. acuminatus population.

Discussion
The established host-parasitoid associations are well known in the entomological literature (Kenis et al., 2004;Wegensteiner et al., 2015).
In conclusion, it should be noted that the discovery of new host-parasite associations expands the knowledge about the ecology of bark beetles in Bulgaria.

Table 1 .
Main characteristics of the studied pine plantations LocalityGeographical coordinates Altitude, m a.s.l.

Table 2 .
Number, parasitism and relative abundance of braconid species in the parasitoid complex