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Silva Balcanica, 14(1)/2013

DISPERSAL OF MALE BUTTERFLIES OF PINE PROCESSIONARY MOTH (THAUMETOPOEA PITYOCAMPA)

Plamen Mirchev, Georgi GeorgievForest Research Institute – Bulgarian Academy of Science

Gesho GeshevForest Protection Station – Plovdiv

Abstract

In Central Bulgaria, in a region of expansion of the pine processionary moth (Thaumetopoea pityocampa), pheromone traps were set in 5 sample plots: one of them in a strongly attacked habitat at the border of species distribution and the rest ones – outside the range in a distance 5.08 km, 23.57 km, 30.89 km and 41.59 km, respectively. In the studied area the flight period of male butterflies of T. pityocampa is approximately 120 days, from June to the end of September, with a distinct peak in the beginning of August. Male butterflies have good flight capabilities and are able to fly over considerable distances over 40 km. The predominant part – 88.3% of the butterflies fly in the habitat and at a distance of up to 5 km from it, and only 5% of the butterflies fly over 30 km from the boundaries of the habitat.

Two types of traps were used in the experiment and their efficiency has been compared. It was proved that the superiority of one type of trap is due to design and technological advantages.

Key words: Thaumetopoea pityocampa, dispersion, male butterflies

INTRODUCTION

Pine processionary moth, Thaumetopoea pityocampa (Den. & Schiff.) (Lepi-doptera: Thaumetopoeidae), is the most significant leaf-nibbling pest in pine forests of Bulgaria, causing substantial economic damages. Caterpillars, as hazardous aller-gens, aggravate the recreation functions of suburbia and resort forests.

An expansion of T. pityocampa is observed in the country, determined by a number of environmental factors and biological characteristics of the species (Mirchev et al., 2011). Dispersion is specific for different species. For instance, in Lymantria dispar L. populations it takes place at larval stage, the decisive role being played by the movement of the newly-hatched larvae by the wind. In pine proces-sionary moth populations, this is done by the imago. In this aspect, the expansion rate of the species depends to a great extent on flight abilities of butterflies. With fe-male individuals they are relatively limited, so they can fly over comparatively short distances, a maximum of up to 2 km (Demolin, 1969b).

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Jactel еt al. (2006) prove that pheromone traps can be a reliable method for monitoring the populations of T. pityocampa.

The aim of this study is to establish some biological distinctive features of pine processionary moth through the use of pheromone traps: the timing and dura-tion of adult emergence period, as well as flight abilities of male butterflies of pine processionary moth, as an element of the pre-conditions for the expansion of the pest.

MATERIALS AND METHODS

For the purposes of this study, five experimental sites were established in Cen-tral Bulgaria, with 3 pheromone-baited traps placed in each of them, to capture T. pityocampa (Table 1). In the studied region, an expansion of pine processionary moth is observed since 1999. A considerable degree of attacks by pine procession-ary moth was recorded in the pine stand near the village of Golyamo Dryanovo in 2010 (the year preceding the setting of the experiment). One of the sample plots was established near the village of Golyamo Dryanovo, which is at the border of species’ distribution, and the rest plots are eastbound from it: Kazanlak (5.08 km), Maglizh (23.57 km), Vetren (30.89 km) and Gurkovo (41.59 km). The distance from the boundary of T. pityocampa area to the relevant site was measured by air through Google Earth.

The pheromone traps were set on 1 June 2011. The setting date was deter-mined in compliance with the flight times of the species reported (Zankov, 1960). Checking of the traps was done at an interval of two weeks and continued until 13 October, when no butterfly was found caught in any of the traps. Sticky bottoms of the traps were periodically replaced. In Golyamo Dryanovo and Kazanlak – the sites with the highest numbers of butterflies caught – this was done after every checking. Two types of traps were used in each site: Omnia-trap (2 traps) and Delta-trap (1 trap).

Table 1. Main characteristics of studied areas

Locality Geographical co-ordinates of sample plotsAltitude a.s.l., m

Distance from the periphery of T. pityocampa distribu-

tion, kmGolyamo Dryanovo 42º40’22.0”N; 25º14’45.5”E 453 0Kazanlak 42º41’35.4”N; 25º22’30.2”E 571 5.08Maglizh 42º36’26.3”N; 25º35’06.3”E 339 23.57Vetren 42º37’01.8”N; 25º40’34.3”E 319 30.89Gurkovo 42º39’24.6”N; 25º47’27.5”E 327 41.59

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RESULTS

Time period and distance of flight of male butterflies of T. pityocampaThe results of the experiment give information about at least two indicators of

pine processionary moth’s biology. This is the flight period and the flight abilities, such as length of flight for the male butterflies of the species.

For the studied region, the emergence of male individuals lasts from June until the end of September (Table 2), i.e. they have an extended flight period, which is within 120 days.

Table 2. Caught butterflies in pheromone traps in sample plots

Sample plots

Type of

traps*

Dates of checking of pheromone traps24 June

7 July

21 July

4 Au-gust

18 Aug.

1 Sept.

14 Sept.

28 Sept.

13 Oct. Σ

Golyamo Dryanovo

Om 14 31 25 26 17 42 14 1 0 170

Dt 4 28 25 39 22 20 8 0 0 146Om 31 29 21 45 21 31 25 2 0 205Σ 49 88 71 110 60 93 47 3 0 521

Kazanlak

Om 1 5 17 48 32 19 6 0 0 128Dt 0 0 10 16 19 7 0 0 0 52Om 1 4 9 33 28 24 1 0 0 100Σ 2 9 36 97 79 50 7 0 0 280

Maglizh

Om 0 0 6 14 9 0 0 0 0 29Dt 0 0 1 0 4 1 1 0 0 7Om 0 1 9 4 10 0 0 0 0 24Σ 0 1 16 18 23 1 1 0 0 60

Vetren

Om 0 0 3 5 4 1 0 0 0 13Dt 0 0 0 3 2 0 0 0 0 5Om 0 0 3 5 3 2 0 0 0 13Σ 0 0 6 13 9 3 0 0 0 31

Gurkovo

Om 0 2 2 0 1 0 0 0 0 5Dt 0 0 3 0 3 0 0 0 0 6Om 0 1 1 1 1 0 0 0 0 4Σ 0 3 6 1 5 0 0 0 0 15

Total 51 101 135 239 176 147 55 3 0 907

*Type of traps: Omnia-trap (Om); Delta-trap (Dt)

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The number of male butterflies during this period has polynomial trend, with a distinct peak in the beginning of August (Fig. 1).

Fig. 1. Flight dynamics of male butterflies of T. pityocampa

In the most remote sites – Vetren and Gurkovo, butterflies were caught in the traps during the species’ peak flight period in July and August.

Results of the experiments show that male individuals of pine processionary moth have good flight abilities and are able to fly over considerable distances (Table 2). Butterflies were found in traps located in a distance of 41.59 km from the pe-riphery of the species’ habitat. Most probably, male individuals are capable to cover longer distances if the place of pupation they have flown from is not at the boundary but further inside the habitat.

The dispersion of male butterflies of T. pityocampa has clearly expressed ex-ponential trend (Fig. 2). Predominant part – 88.3% of the butterflies fly inside the habitat and at a distance of up to 5 km from it, and only 5% of butterflies fly over 30 km from the habitat boundary.

Fig. 2. Dispersion of caught male butterflies of T. pityocampa

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Effectiveness of pheromone trapsTwo types of traps were used in the experiment: Omnia-trap and Delta-trap. It

made it possible to compare their efficiency. The data in Table 3 explicitly show the superiority of Omnia-trap type, where the average number of butterflies caught was almost 60% higher. This greater efficiency is determined by at least 3 factors: the first two connected with the design, and the third one – technological:

- With Omnia-trap the sticky surface is 28% larger (Table 3).- With Delta-trap there are two openings, whereas with Omnia-trap the open-

ings are on all four sides, which provides better dispersion of the attracting smell of the dispenser and better accessibility for attracted male butterflies.

- Delta-traps are less efficient due to the lower quality of used sticky sub-stance. With this trap type we had the opportunity to observe how a butterfly entered the trap and after flying around it flew out without being stuck.

Parameters such as colour also influence the efficiency of traps, as reported by Athanassiou et al. (2007).

Table 3. Effectiveness of pheromone traps

Type of traps

Square surface of adhesive

surface, cm²

Number of traps

Number of caught but-

terflies

Average number of caught but-terflies on a

trap

Average num-ber of caught butterflies on 10 cm² adhe-sive surface

Omnia-trap 460 10 691 69.1 1.58

Delta-trap 360 5 216 43.2 1.20

DISCUSSION

Data on time and duration of the imago period of pine processionary moth have been reported by Zankov (1960). The author established these parameters by pupae collected in the field and put in insectarium. Using material collected from Hisarya, which is within the area of the current study, it has been established that the start of the flight is around 20 June and it lasts until 8 – 25 July in different years. These results differ significantly from the ones obtained in the current study, where the maximum of the flight of male butterflies is in the beginning of August, i.e. about 2-3 weeks after the end of the imago period reported by the cited author. These differences could be due to the probably limited experimental material, which has not been recorded in the publication of Zankov (1960). The question has not been completely clarified in the literature, as the time of imagination of diapausing pupae established for this species (Georgiev, 1959), a diapause which can last for up to 6 years (Demolin, 1969a).

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Chenchouni et al. (2010) reported a peak of male butterflies caught in the period between 16 and 24 August in Batna, which is a high mountain region in North-eastern Algeria. In Magnesia, Thessaly, Central Greece this maximum is at the end of August and the beginning of September (Athanassiou et al., 2007). The situation in Portugal is similar (Zhang, Paiva, 1998), and it is about 1 month after the one established in the current study. The current obtained data confirm the difference in the phenology of the local population from the typical Mediter-ranean form – what has given Tsankov et al. (1996) grounds to separate it as T. pityocampa bulgarica.

Bulgarian entomological literature contains indirect data on the dispersion of male butterflies of pine processionary moth. T. pityocampa was established and re-ported for first time in Bulgaria in 1906, when Drenovsky (1923) captured a male specimen at light in the region of Sofia at the foot of Vitosha Mt. In the same moun-tain male individuals have been found within the band of altitude from 1600 to 1800 m by Vihodtsevskiy, Gogov (1963) and Nestorova (1971). Apart from male individu-als, no other phases of the species’ evolution, caterpillars and egg-batches have been found. The closest habitat of the species is in the region of the town of Dupnitsa, at a distance of about 50 km.

Despite of the great dispersion of male butterflies, Jactel еt al. (2006) estab-lish dependence between the number of individuals caught in the traps and the num-ber of winter nests in a particular habitat. Results obtained in this study illuminate this fact in the aspect that there is, on the one hand, flight at long distances but the predominant mass of male individuals fly within the limits of the habitat. It should be noted, however, that the finding of Jactel еt al. (2006) does not find confirmation in the studies of Tiberi, Nicoli (1984) and Chenchouni et al. (2010).

The ability for distant flights has an impact on the genetic diversity of the population. Salvato et al. (2005) have established homogeneousness of mitochon-drial haplotypes of adult males caught in traps and the caterpillars from the particular habitat, but in regions of expansion of pine processionary moth occurrence trapped males were recruited over a wider area than local moths because haplotype diversity was higher than that of larvae.

In this study, sample plots with pheromone traps are located around settle-ments or roadside forestation. It remains an open question whether the dispersion of male moths of pine processionary is homogeneous in the four cardinal directions and how it is influenced by such factors as the lights of vehicles on the road and those in urban areas.

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Chenchouni, H., K. Zanati, A. Rezougui, A. Briki, A. Arar. 2010. Population monitoring of pine proces-

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