IntroductionBaculoviruses are enveloped viruses that have doublestranded, circular DNA genomes ranging in size from 80 to 180 kbp (1,2). Baculoviruses have been isolated from more than 600 insect species belonging to the orders of Lepidoptera, Hymenoptera, Diptera, Orthoptera, Coleoptera, Neuroptera, Thysanura, and Trichoptera (3). The most notable characteristic of baculoviruses is the occlusion body (OB). The occlusion body is a crystalline matrix composed of a protein called polyhedrin, which provides protection to the virions in the environment against proteolytic and chitinolytic enzymes in the decomposing larvae and spreads infection among insects (4,5). Baculoviruses have been taxonomically divided based on their OB morphology into nucleopolyhedroviruses (NPVs) and granuloviruses (GVs), forming polyhedra and granula, respectively (6). In the NPV, the OB ranges in size from 0.4 to 5 µm in diameter and contains several virions (7,8). The OBs of NPVs are most easily seen under light microscope due to their larger size and their light refractory polyhedral structure. The OBs of GVs, called granula, appear as dark granules and are comparatively more difficult to resolve under light microscope. They are ovoid-shaped and about 500 nm long and 20 nm wide (8,9).The family Baculoviridae is divided into 4 genera according to common biological and structural characteristics and patterns of host associations: Alphabaculovirus, which includes lepidopteran-specific baculoviruses and is subdivided into Group I or Group II based on the phylogenetic analysis of the polyhedrin genes from different baculoviruses; Betabaculovirus, comprising lepidopteran-specific granuloviruses; Gammabaculovirus, which includes hymenopteran-specific baculoviruses; and finally Deltabaculovirus, which contains dipteran-specific baculoviruses (4,10,11).Malacosoma neustria (Linnaeus, 1758) (Lepidoptera: Lasiocampidae), known as the European tent caterpillar, is an important defoliator of various fruit trees such as apple, pear, and plum; wild and ornamental trees and shrubs, including oak and rose species, oleaster, sea buckthorn, barberry, elm trees, willow, poplar, and aspen; and birch, particularly in eastern and central Turkey (12)(13)(14). The caterpillars first eat the buds and then leaves of the trees. During some years their population reaches such high numbers that they leave the trees completely leafless. Factors such as weather conditions and natural enemies including predators, parasitoids, and pathogenic microorganisms have historically been important regulatory elements in the population cycles of this insect.The key microbial pathogens of this insect include NPVs (15). The presence of NPVs in M. neustria was reported by several authors (16-31). In 2009, Demir et al.