Evaluation of biological control agents against Monochamus galloprovincialis (ColeopteraCerambycidae) in Portugal

Laburpena

Pine wilt disease is the result of a complex interaction between a nematode, a host tree and an insect vector. The pine wood nematode (PWN) Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle is the causal agent, being pines the most important hosts. To be dispersed between hosts the nematode requires a vector insect, being the most effective the cerambycid beetles of the genus Monochamus Dejan. The first detection of PWN in Portugal occurred in 1999, and in 2001 it was associated with its local vector; the pine sawyer Monochamus galloprovincialis (Olivier). Since then M. galloprovincialis has been the main focus of a complex and detailed strategic plan to fight this disease. Management and control strategies against PWN are directed in three ways; controlling the nematode’s populations; creation of trees resistant to the disease and avoiding the spread of the nematode by the dispersal of vector insects, being presently the most effective one. This is done with the implementation of strict sanitary measures in affected forests, by locating, felling and removing/destroying symptomatic trees during autumn and winter, to prevent adult emergences carrying the PWN. During spring and summer, M. galloprovincialis adults are exhaustively controlled by the use of baited traps, diminishing beetles populations. Despite such efforts, the PWN still causes significant mortality in native maritime pine forests in Portugal, and between 2000 and 2007 the number of felled pine trees with wilting symptoms significantly increased, causing significant economic and environmental impacts. Simultaneously, the spread of wilt disease to Spain underlines the necessity to develop and promote innovative control strategies against this sanitary problem. With the intention of developing new biological control strategies, the works here presented were focused on: i) improving a laboratory reared population of M. galloprovincialis, ii) reveal M. galloprovincialis actual distribution and the associated parasitoid guild, iii) discover the most promising entomopathogenic fungi associated with this insect and an effective method for field application. The initial studies concerning the artificial rearing of a laboratory population of M. galloprovincialis allowed the attainment of adults on shorter periods and with less effort. Such objective was successfully accomplished by the development of an artificial rearing substrate which is cheaper to produce and does not require fresh pine material recently extracted from live trees. Concerning the unveil of the insect distribution across the country and its parasitoid guild, it was found that the cerambycidae is present on more than 90% of the surveyed regions, without showing signs of strong susceptibilities to the edaphoclimatic variations of each site. Also, the parasitoid guild associated with this insect showed to be relatively disperse and diverse across the studied regions. Most of the parasitoids found were larval parasitoids, being the most common among them Cyanopterus flavator (Fabricius). Regarding the assays with entomopathogenic fungi, it was revealed that Beauveria bassiana (Bals.-Criv.) Vuill was an important mortality agent for M. galloprovincialis adults while Metarhizium sp. strongly affected the larvae of this insect. A successful application method was also developed using fiber bands to impregnate entomopathogenic fungi under laboratory conditions. It is now possible to state that it was comprehensively studied the parasitoid guild associated with the pine sawyer and the effects of the more common entomopathogenic fungi found in Portugal and associated with this beetle, being now unveiled the basis for a biological control program against M. galloprovincialis populations.