WORKING PARTY ON POPLAR AND WILLOW INSECTS AND OTHER ANIMAL PESTS 169 170 PRESENT SITUATION OF THE POPULATION OF N. OLIGOSPILUS FOERSTER (=N. DESANTISI SMITH) (HYM.: TENTHREDINIDAE) IN THE TAFI VALLEY, TUCUMAN, ARGENTINA: FUTURE CONSIDERATIONS Mariela Alderete1, Gerardo Liljesthröm Nematus oligospilus Foerster (= N. desantisi Smith), a Holartic species whose larvae feed on leaves of Salix spp., was recorded in Argentina and Chile in the 1980´s. In the delta of the Paraná river (DP) and in the Tafí valley (VT) in Argentina, the sawfly larval populations attained high densities and severe defoliations were observed: in 1991-92 and 1993-94 in DP, and in 1990-91 and 1994-95 in VT. In VT the sawfly larvae have remained at low density since then and trials excluding natural enemies showed that larval survivorship was significantly higher than in the controls. Further, an intensive sampling over five consecutive years allowed us to perform a key-factor analysis, and larval mortality, possibly due to predators (polyphagous Divrachys cavus was the only parasitoid recorded from less than 1% host larvae), was density-dependent and supposed to be capable of regulating the sawfly population. The DP and VT regions have different ecological conditions: while DP has broad and continuous willow plantations and a humid-temperate climate, VT is an elevated valley bordered by mountains with a sub-humid cold climate (rains are concentrated in spring and summer) with small and rather isolated willow forests. Apart from these differences, both regions show very low parasitoidism, outbreaks shortly after being recorded in the area, and no significant differences between outbreak and no-outbreak years with respect to mean and mean maximum temperatures as well as in accumulated rainfall. These results permitted to suspect that in DP, natural enemies (general predators) are playing an important role in limiting the sawfly larval population. It is therefore very important to apply the same methods of analysis of mortality used in VT to study N. oligospilus in DP. Key Words: willow, sawfly, larvae, predators, population dynamics. 1 PROIMI-CONICET, Av. Belgrano y Pje Caseros, 4000 Tucumán, Argentina. E-mail: [email protected]; [email protected] FAO ID 148 171 THE PARASITOIDS OF NEMATUS OLIGOSPILUS FOERSTER (HYM.: TENTHREDINIDAE) IN CALIFORNIA (USA) FOR A PROGRAMME OF BIOLOGICAL CONTROL IN ARGENTINA Mariela Alderete1, Patricio Fidalgo Nematus oligospilus Foerster (=Nematus desantisi Smith) occurs as a pest of willows in the southern areas of South America, South Africa and New Zealand. It is particularly serious in Argentina where heavy annual losses are caused to the wood industry in the Delta of the Paraná river, Buenos Aires, Argentina. The larvae of the sawfly feed on leaves of willow and infested trees may suffer serious setback and even die. This forest pest is native to the Holartic Region where it occurs throughout Eurasia and North America. Use of chemical insecticides and Bt methods are impracticable. Biological control seems to be the only economically and ecologically practical way to control populations of N. oligospilus introduced into the Southern Hemisphere. A review of the taxonomic structure of parasitoids known to attack Nematus and Pristiphora species in the Holarctic region showed that the parasitoids of the subfamily Camplopleginae and Ctenopelmatinae as well as other monophagous and oligophagous ichneumonids (especially Tryphoninae) are the most important components of the complex of natural enemies associated with these Nematinae sawflies. During a preliminary survey carried out in California, USA in the spring and summer of 2000 to determine the possibilities of biological control of N. oligospilus, the following parasitoids were found associated with the sawfly : Trichogramma aurosum Sugonjaev and Sorokina, T. Sibericum Sorokina (Trichogrammatidae) and Olesicampe californica Cresson (Ichneumonidae, Campopleginae). The tricogrammatids are idiobiont endoparasitoids of eggs causing between 55 and 95% of parasitism, while the ichneumonid is a koinobiont endoparasitoid of larvae causing between 25 and 50% of parasitism in the field. The parasitoids reared during the course of those investigations were identified by Dr. John Pinto (University of California at Riverside) and Dr. Charles C. Porter (USDA Gainesville, Florida). Key Words: Ctenopelmatinae, Campopleginae, Trichogramma aurosum, T. sibericum, Olesicampe californica, sawfly of willow. 1 PROIMI-CONICET, Av. Belgrano y Pje Caseros, 4000 Tucumán, Argentina. E-mail: [email protected]; [email protected] FAO ID 149 172 THE THREAT OF THE AMBROSIA BEETLE, PLATYPUS SULCATUS (=MUTATUS) TO WORLD POPLAR RESOURCES René Alfaro1, Paola González, Raúl Villaverde, Nilo Battaglino, Gianni Allegro, Leland Humble The life cycle, hosts and damage caused by Platypus sulcatus (=mutatus) to resources of Argentina are described. This insect, native to the subtropical area of Eastern South America, has extended its range in Argentina, reaching as far South as Neuquén in the Argentinian Patagonia. The damage is caused by the adults, which bore large gallery systems into living poplars, Salix and many other broadleaf species, including fruit trees such as walnuts and avocados. The galleries not only degrade the lumber, but weaken trees which often fall during windstorms. A recent introduction to Italy demonstrates that this insect can be transported long distances between countries, and therefore presents a threat to poplar cultivation world-wide. Preliminary results of research aimed at developing a pheromone-based detection and control system are presented. Key Words: Platypus sulcatus, poplars, pheronome-based detection. 1 Canadian Forest Service, Natural Resources Canada, Pacific Forestry Centre, 506 W Burnside Road, Victoria, B.C., Canada V8Z 1M5. E-mail: [email protected] FAO ID 81 173 RELATIONSHIPS BETWEEN POPLAR (POPULUS SPP.) STAND STRUCTURAL VARIABLES AND LEVELS OF AMBROSIA SMALL-BORER ATTACKS (MEGAPLATYPUS PLICATUS) (BRÉTHES) Alejandro Aparicio1, Gerardo Liljesthröm, Fabio Achinelli, Raúl Marlats Ambrosia small-borer (Megaplatypus plicatus (=Platypus sulcatus)) is a major plague in poplar plantations (Populus spp.) of Argentina. Models for damage prediction are required as key components of an integrated management strategy. For this reason, it is necessary to study the spatial patterns of borer attacks that affect plantations during the season of adult emergence. The aim of this work is to determine relationships between levels of small-borer attacks and stand structural variables of poplar plantations in Alberti, Buenos Aires, Argentina. This study was done during the 2003-2004 adult emergence season, on 16 permanent plots (PSP) consisting of 100 trees each (n=1600 trees). No significant relationship was found between the average diameter at breast height (DBH) of trees and the total number of male galleries (MG) present in each PSP (r= 0,34). Nine out of the ten PSP with highest number of attacks, showed an aggregate spatial pattern of MG, which fitted to a negative binomial probability distribution (mean k=0,72); in only one PSP, MG spatial pattern was random, which fitted to a Poisson probability distribution. As the number of attacks within each PSP increased, the number of trees attacked also increased; a multiplicative relationship was found between both variables (r2 =0,97). When trees were rearranged and grouped according to number of attacks received, a noticeable DBH heterogeneity was observed within each group. However, when mean DBH of each group is considered, a tendency appears evident for increasing number of attacks in highest mean DBH (r= 0,85). As regards MG viability, only 23% of them showed signs of activity in the April 2004 census. Concentration of attacks in some of the largest trees would explain the occurrence of aggregate spatial patterns within most PSPs. Even though there seems to be a tendency for high DBH class trees to present a greater number of attacks, DBH of individual trees is insufficient as the only input variable to predict number of attacks per tree. Results of this screening phase would indicate that stand-scale attacks are being produced by local populations of the plague, and that stand history and location could be as important or sometimes more decisive factors than structure in defining the level of small-borer attacks. The high number of inactive MG at the end of the emergence period reveals the presence of some factors that would significantly affect the processes involved in the transition from MG to larval, viable galleries. Key Words: small-borer, Megaplatypus plicatus, stand structure, attack distribution, Populus, Argentina. 1Cátedra de Silvicultura, Fac. de Cs. Agrarias y Forestales UNLP – CIC Buenos Aires, CC 31, B1902WAA, La Plata, Buenos Aires, Argentina. E-mail: [email protected] FAO ID 79 174 PHYTOSANITARY CONDITION OF POPLARS AND WILLOWS IN CHILE Aida Baldini1, Marcos Beèche, Angelo Sartori As a result of systematic and non-systematic phytosanitary surveys conducted by the Agriculture and Cattle Service (SAG) and the National Forest Corporation (CONAF), it has been possible to determine the current phytosanitary condition of the genera Populus and Salix in Chile. The results suggest that the principal problems are present in urban trees, clumps and windbreaks located in peri-urban locations, with some problems in Regions V and X and worst conditions in the Metropolitana Region.