Electrophysiological and behavioral responses of Tomicus minor (Coleoptera: Scolytidae) to host volatiles

To screen for host volatiles that effectively attract the lesser pine shoot beetle, Tomicus minor (Coleoptera: Scolytidae), an important forest pest, water vapor distillation extraction and gas chromatography-mass spectrometry were combined to analyze volatiles emitted from uninfested and infested shoots of Pinus yunnanensis (Pinaceae). Electroantennography and Y-tube olfactometer behavioral tests were used to compare and analyze the responses of male and female beetles to each of selected eight compounds. The spectrometry results showed that monoterpenes are the primary chemicals emitted by P. yunnanensis. The electroantennogram responses of adult T. minor to six of the plant compounds peaked at 10 μg/μL; the exceptions were terpinolene and myrcene, which had maxima above 100 μg/μL. (+)-α-Pinene and β-phellandrene were strongly attractiveto the male and female adults.

Intraspecific and interspecific attraction of threeTomicusbeetle species during the shoot-feeding phase

The shoot beetlesTomicus minor, Tomicus yunnanensis, andTomicus brevipilosushave been decimatingPinus yunnanensistrees for more than 30 years in Southwestern China. To understand the chemical ecological relationship between pines andTomicus, and among the three beetle species, we compared the attraction of these beetles to damaged shoots, extracts from damaged shoots, and volatiles from damaged shoots collected by the dynamic headspace sampling method. Experiments were performed using a modified open-arena olfactometer. The maleT. minorand both sexes ofT. brevipilosuswere more strongly attracted to damaged shoots than to undamaged shoots and they showed attraction to shoots damaged by the same species. FemaleT. minorand both sexes ofT. yunnanensiswere attracted to shoots damaged by femaleT. brevipilosus. The three beetle species were attracted to shoot extracts and dynamic headspace volatiles from shoots damaged by the same species and sex. FemaleT. minorand maleT. yunnanensiswere also attracted to dynamic headspace volatiles from shoots damaged by both sexes ofT. brevipilosus. The results suggested that specific semiochemicals that are induced or produced byT. brevipilosusalso attractT. minorandT. yunnanensis. The semiochemicals in damaged shoots affect the attraction of the three beetle species and play an important chemical communication role in weakening the host trees during the beetles’ shoot-feeding phase.

Performance ofTomicus yunnanensisandTomicus minor(Col., Scolytinae) onPinus yunnanensisandPinus armandiiin Yunnan, Southwestern China

Pine shoot beetles,Tomicus yunnanensisKirkendall and Faccoli andTomicus minorHartig (Col., Scolytinae), have been causing substantial mortality to Yunnan pine (Pinus yunnanensisFranch) in Yunnan, southwestern China, whereas only a few Armand pine (Pinus armandiiFranch) were attacked by the beetles. In order to evaluate the suitability ofP. armandiias host material for the twoTomicus, adults of bothTomicuswere caged on living branches and felled logs of the two pines during shoot feeding and trunk attack phase, respectively. More beetles survived on the living branches ofP. yunnanensisthan onP. armandii.Tomicus yunnanensisandT. minorproduced similar progeny in the logs of the two pines. The sex ratio and developmental period were not affected by host species, but the brood beetles emerging from Armand pine weighed less than those from Yunnan pine, suggesting thatP. armandiiare less suitable to be host ofT. yunnanensisandT. minor.

Coexistence and Competition betweenTomicus yunnanensisandT. minor(Coleoptera: Scolytinae) in Yunnan Pine

Competition and cooperation between bark beetles,Tomicus yunnanensisKirkendall and Faccoli andTomicus minor(Hartig) (Coleoptera: Scolytinae) were examined when they coexisted together in living Yunnan pine trees (Pinus yunnanensisFranchet) in Yunnan province in Southwest China.T. yunnanensisbark beetles were observed to initiate dispersal from pine shoots to trunks in November, while the majority ofT. minorbegins to transfer in December.T. yunnanensismainly attacks the top and middle parts of the trunk, whereasT. minormainly resides in the lower and middle parts of the trunk. The patterns of attack densities of these two species were similar, but withT. yunnanensiscolonizing the upper section of the trunk andT. minorthe lower trunk. The highest attack density ofT. Yunnanensiswas 297 egg galleries/m2, and the highest attack density ofT. minorwas 305 egg galleries/m2. Although there was significant overlap for the same bark areas, the two species generally colonize different areas of the tree, which reduces the intensity of competition for the relatively thin layer of phloem-cambium tissues where the beetles feed and reside.

Fungi associated with Tomicus minor on Pinus sylvestris in Poland and their succession into the sapwood of beetle-infested windblown trees

The study identified and measured frequency of fungal species associated with Tomicus minor (Hart.) on Pinus sylvestris L. (Scots pine) in Poland. Additionally, fungal succession in P. sylvestris sapwood was investigated during a 12 week period following an attack by this insect. Fungi were isolated from five populations of overwintered adult beetles and their galleries with 59 species of fungi being represented among the 2880 cultures obtained. The most frequent species, Ophiostoma canum (Münch) Syd. & P. Syd., Hormonema dematioides Lagerb. & Melin, and Ambrosiella tingens (Lagerb. & Melin) L.R. Batra, appeared to be specifically associated with T. minor. The succesional changes in species composition during a 12 week period following an attack by T. minor were observed. The pattern of fungal succession in P. sylvestris sapwood essentially agreed with a general scheme of fungal succession in tree sapwood infested by bark beetles. Ambrosiella tingens was the first invader of sapwood and occurred most frequently in its deeper layers. Ophiostoma canum, H. dematioides, and other molds were also often isolated from the sapwood; however, they were most common at a depth of 5 mm during the initial phase of fungal colonization. Later, Ophiostoma canum followed A. tingens in the sapwood invasion.