The extent of damage on sessile and especially pedunculate oak, varied in past several years. Results of acorn analysis from 1991 year crop display an average acorn attack extent in Croatian lowland forests of pedunculate oak. Obviously, large amount (59%) of ripened or ripening acorn is lost due to a several destroying organisms. Only those eliminating factors that attack pollinated and growing acorn have been taken into account. It means that even more detrimental organisms, like defoliating insects and some fungi reduce potential quantity of acorn even before female flowers have been pollinated. Largest amount of damage is caused by acorn weevils (Curculio spp.) and small forest rodents (25% and 18% respectively). Among forest rodents two species occurred most consistently and are typical for researched area: yellowthroated forest mouse (Apodemus flavicollis) and forest vole (Clethrionomys glareolus). Their detrimental role starts in September and October when most of the sound acorn fall occurs and they feed on it on the ground. By doing this, they leave parts of acorn cups and nutshells which can be counted and this is how we measured their noxious effect. Beneficial aspects of their activity (mice for example) include collecting and underground burial of collected acorn. Some of the collecting spots are forgotten and acorn is given a better chance to successfully root itself in forest ground. Some researchers evaluated yet another beneficial role of this rodents, i.e. their selective feeding with infected acorn and reduction of acorn weevils larval stages. In this research we haven’t measured this beneficial impact. Although we do not deny existence of such collecting and feeding behaviour we consider this to be of lesser importance in holistic approach, especially when other rodent related noxious effects on oak seedlings and young plants are known. Another research that is starting in the same research area is dealing exclusively with rodent related problems in oak regeneration.
Second most important insect group encompassed with this research were acorn moths with two most numerous species: Cydia amplana and C. splendana. Caterpillars of these two moths were found during their feeding period inside nutshell. The amount of damage varied on different locations but average value reached 12%. Moth damages were easily dis-tin-guished by the presence of caterpillars itself, their droppings enveloped with web and oval exit holes . 4% of total damages are not differentiated because they comprise several noxious agents. Most numerous, (although relatively small in total extent), was gall inducing cynipid, Andricus quercus calicis. Their galls were recorded in various stages of acorn and gall development and their relative abundance varied between collecting sites and research years. It seems that especially in poor crop years their relative damaging effect rose, keeping the absolute population density stable. We speculate that this originates from their relatively early attack period when there is sufficient quantity of acorn producing female flowers.
Acorn weevils occupied our utmost attention so the whole research was oriented toward better knowledge of their ecological characteristics and population strategies in various biotops and poor seed crop years. As it has been mentioned earlier, the average amount of their detrimental impact reached 1/4 of total acorn production. This value varied but acorn weevil prevailed as the most important one among noxious seed insects. Species composition differed from site to site, but on the average, Curculio glandium was the most numerous one. Curculio elephas and C. venosus were the two other species recorded in this research. C. villosus weevils were reared in laboratory experiments their larvae been collected in field soil samplings. Only the first three species are acorn pests while C. villosus larvae develop inside applelike galls of gallwasp Biorhiza terminalis. Larval stage was thoroughly analysed, especially their underground period of development. Numerous diggings were made in various forest soil types and different vegetational coverages. Soil probes were dug 30 cms deep and throughout the whole year in a 15day period interval. Analysis of probes (25×25×30 cm) was done in the field with great care and in a scrutinised way. This way we could be sure when conclusions were made about weevil’s life cycle and its population strategy. Weevil’s larval stage was present in soil probes in all seasons. There was absolutely no field soil sampling day without larval presence. Fully grown larvae emerge from fallen acorn in relatively short time and immediately bury themselves in the forest floor. The faster they complete this action, the lesser is risk of being attacked from their natural enemies. Almost 75% of all larvae built their underground chambers between 5 and 15 centimetres deep. Only about 20% of stayed in shallow surface zone down to 5 cms deep. The rest of them, which is about 10% descended deeper. Our explanation of such strategy is that by positioning themselves in this manner they minimised the risk of being destroyed by unsuitable climatic conditions or attacked by surface and shallow subsurface foraginig entomophages. On the other hand, they were still able to successfully ascend in adult stage and brake free, through 15 centimetres of forest soil. Seasonal findings of weevil’s depth dispersal in 3-dimensional view showed no changes during the year. It means that, once buried and positioned in soil chamber, larvae did not move or change their position. Their spatial distribution is insular-like, being dependable on acorn producing oaks and their distribution in the forest. These findings and data on spatial distribution of weevils during their underground phase gave us some clues to define prognosis methods.
Pupal stage was recorded in the field and during larval rearings in laboratory experiments. First pupae were found in soil probes in the middle of July. By the beginning of September there were no more pupae in the soil (only freshly ecdysed adults and larvae). Pupal stage is the shortest one in weevil’s life cycle. What surprised us most was the fact that freshly ecdysed adult weevils did not leave their chambers immediately after pupation. Neither in our field experiments, nor in laboratory rearings from 1989 until today, did weevils emerge from soil chambers directly after pupation. This contradicts with one-year cycle theory proposed by some authors which we did not find to exist in our research area, not in the slightest percentage. One of the logical reasons could be the condition of forest soil in midsummer period. Being mostly clayish in structure in their dry phase these soils are extremely hard (more than single shovel was broken during summer diggings), so weevils would have considerable difficulties ascending through dry and sometimes concretelike surface zone. Instead, they emerged earlier while soil was still reasonably wet and pliable. Other reasons for such behaviour arise from weevil’s phisiological development and capability to end its dormant period.
Adult stage was monitored in many ways and appeared as one of the possible target phases for population reduction. For emerging adult weevils, special forest floor traps were designed. Wooden frames (2×2 and 2×1 meters) were positioned on promising spots (remainings of last year acorns or young one or two year oak saplings). Opening part of the frame was covered with fine plastic mesh. The whole cover was fitted properly so emerging insects could not escape without been recorded. Some traps stayed in same position more than one season and longest possible use of such wooden trap (with seasonal repairs) could be three years. Trap inspection was done periodically. Careful opening and inverting of plastic mesh cover assured easy collecting of emerged weevils. This was done in early morning hours when insects were clinging on plastic mesh and did not have any chance for escape. Such trapping method provided valuable data on weevils life cycle and helped to rightly predict their appearance in forest canopy. Being permanent on the same forest floor area and excluding yearly input of freshly soil entering larvae, results of consecutive three year catch results can give us some idea on weevil’s population breakage regarding length of their diapausing period. Total surface area covered with 4 permanent traps amounted 6 m2. In a three year period 67 adult weevils were collected on these traps. 43 emerged in 1991, 20 in 1992 and only 4 in 1993. It should be stressed here that traps were positioned in the forest by the end of march 1990. Only one weevil was recorded that year (one female on 29th of may). 1991 
was the first year of massive emergence and heavy weevil’s attack. To explain this, data on acorn production in previous years must be known. Bumper crop occurred in research area in 1989. Next one was in 1993. Presuming that one year cycle does not exist, it is understandable that 43 weevils emerging in may 1991 originate from larvae which buried themselves during the 1989 acorn fall. Split of population in different diapausing larval cohorts can be calculated from given data. According to our findings 64% of population goes through a two-year cycle, 30% has a three-year and 6% has a four-year cycle. It is possible that some of the larvae stay for even longer period in dormant stage but this portion of population is obviously very small. Determined sex ratio has not significantly changed in emerging cohorts. Its value was 0.47 in 1991, 0.65 in 1992 and 0.5 in 1993. Another important data resulted from forest floor trap catches. We could precisely determine and plot on a time scale weevil’s emergence period. We can conclude that on the average peak of weevil’s emergence occurs in May. In some years they started emerging by the end of April while in another year or different district they emerged as late as the beginning of June.
Period of weevil’s canopy activity was especially interesting because of their possible susceptibility to integrated pest control measures. On reachable lowlying side branches we monitored their activity together with acorn maturation. Copulation and egg laying activity were closely monitored. These behavioural patterns were most easily recorded from the beginning of August to the end of September. Before that period there was no canopy activity recorded. Question arises from the fact that weevil’s emergence ceased by the end of June. Which parts of forest do weevils inhabit in almost twomonth period, before they aggregate on ripening acorn? We have certain indications that some of that time could be spent on bursting young oak leaves (on which adults were feeding in laboratory experiments). This feeding is needed for post emergence, additional buildup of copulatory organs. Proof for this was found in our laboratory experiments with freshly emerged adult weevils (from dugout weevil’s larvae). Though being regularly fed with fresh twigs of forest trees and bushes they never displayed copulation behaviour. Not a single copula was ever recorded from these animals, while freshly collected weevils in the wild (aggregated on reachable fruitbearing oak branches) freely copulated and laid eggs in laboratory, right before our eyes. This suggests that one to two month period is crucial for their development and suc-cessful reaching of complete maturity. We still have to determine their spatial distribution during that time to be sure whether we can take some suppressive measures or not. Egg laying procedure was successfully monitored in the field and in laboratory conditions. Careful observation provided more details about this important behavioural pattern. Copulation, more or less, coincided with egg laying. Very often females were seen with males on their back while piercing an acorn and preparing to lay. As a rule, female would always pierce acorns through the acorn cup. Nutshell is significantly softer bellow the cup and this is probably why piercing is done in this manner. After completing the entrance channel, as deep as its whole snout, female would quickly turn around and insert single egg in the channel. Whole process, from the beginning of piercing activity until egg inserting, lasted from 15 to 30 minutes. Peak of daily activity occurred on warm and quiet afternoons until dark. Several nocturnal field excursions did not reveal significant weevils activity during the night.
As additional control method for monitoring canopy activity we used insecticidal treatments of singular trees or branches. Dropping fauna was collected on white cotton sheets placed underneath treated trees. In this experiments we used synthetic pyrethroids dissolved in water and sprayed with motor atomisers. When higher altitudes were required (over 6-7 metres) we used same insecticides dissolved in mineral oil and applied by thermal fumigators. This way we could reach the highest crowns presuming that weather conditions were adequate. We used slightly stronger doses than prescribed in order to get quicker results. By careful ocular inspection and chemical treatment of chosen trees and acorn bearing branches we gathered more data on species composition and their exact aggregation time on ripening acorns. All this served as decision making cornerstone for correct timing of aerial insecticidal applications.
Real suppressive measures started in 1993 on relatively small forest areas. Only 2400 hectares were treated with one application. Regretfully, from the research viewpoint, this was not a productive year. It happened to be a bumper year and in the other hand, weevil populations have fallen very low (from the previous sound year i.e. 1989). In such situation their detrimental impact was less-ened and we could not evaluate aerial treatments correctly. We expect to be of better luck this year (1995) when we expect massive attack of acorn weevils (first cohort of two-year cycle larvae from 1993 acorn crop). In aerial applications we use small planes with up to two tons pesticide capacity with mounted aerial atomisers. In 1993 we conducted only one treat-ment targeted to acorn weevils while 1995 plans forecast at least two treatments per year. Another important ob-jective is to determine whether early insecticidal applications against defoliators have any effect on emerging larvae (as this treatments are usually conducted during the May). Final acorn analysis from treated and untreated experimental plots will give us better evaluation of application measures.
Very important part of this research dealt with natural enemies of acorn weevils. In all segments of research we tried to i solate possible parasites which could be found in available reference works. During a 6 year period we did not found a single parasitic insect which we could positively connect with any of the weevil species or their development stages. The only and most consistent reductive agent was entomopathogenic fungus Metarrhizium anisopliae, known by the name "green muscardine". We found it on all experimental plots from collected larvae, pupae and adult weevils. It was present on the continent in both pedunculate and sessile oak stands but we found it even in Curculio elephas larvae from Mediterranean holm oak isle belt. Fruiting bodies of this fungus were isolated from above mentioned development stages and microscopic investigation confirmed identification. Field identification of M. anisopliae was relatively easily achieved by green mass of spores which were especially visible on dead larvae. Same diagnostic features were visible on infected (and killed) pupae or adult weevils. Precise evaluation of its detrimental effect could be accomplished only through laboratory rearings of field collected larvae. Adult weevils would emerge from this containers after two years (regularly this happened approximately two months before field emergence in same year). Comparison of emerged larvae and previously enclosed larvae produced accurate evaluation of larval, pupal and adult mortality of 55%. Adult mortality was expectedly lower, compared with that of preimaginal stages. Only few adult cadavers have been found in container soil after detailed excavation (less than 5% of dead weevils). In field diggings we could not judge the extent of M. anisopliae impact. However, around three percent of dugout larvae, pupae and adults showed clear signs of fungus attack (dead specimens covered with green dust). We believe that natural mortality, due to fungus attack occurring in the field, is not negligible. Fungal infection is probably occurring on larval descent in forest soil. Dynamics of attack, biotic potential, microclimate needs and many other questions regarding fungus suitability for biological suppression measures must be solved. Similar control measures have been reported for pests who also spend some of their development time in subterranean environment.
Conifer seed pest analysis started in 1992 with small scale cone collections. Large scale sampling was realised in 1994, when common fir (Abies alba) had a masting year. Being our most important conifer species, fir received most of our research interest. Much of the silvicultural problems regarding reforestation of mixed fir and beech forests arise from absence of fir regeneration and questionable seed production. Even when fir does flower, not much is recorded in next year’s survey on seedling number. In 1994, our samples came from commercially collected fir cones. Shipments from all fir growing parts of Croatia arrived at central collecting place in Forestry institute Jastrebarsko. Here, all the cones were laid out to dry slowly before they went to seed-separating machinery. Complete 1994 fircone harvest weighed 1099 kg (dried cones) or 166 kg of extruded seed. At this point our first phase of sampling procedure started. Random groups of lying cones were isolated and visibly infected were counted. By doing this we evaluated attack of large and easily visible conoseminiphages like 
cone pyralid moth Dioryctrya abietella. Further analysis involved cone breakdown when we registered further cone inhabiting pests. This was the case with cone tortricid moth Barbara herrichiana. At the time of cone collecting (end of September) this moth was in pupal stage while cone pyralid moth was in fully grown larval stage. Movable Dioryctria caterpillars caused us some difficulties in evaluating their average number. Very often they left their cones and wandered on underlying plastic sheets. Another insect left cones as soon they were unloaded from transport vehicles. White, wormlike larvae of Earomyia impossibile pulled out themselves out of cones and in a day or two they pupated. Next stage of sampling was done after seed exclusion. When cone scales, cone spindles and various dirt was separated, we took about 1 litre of winged seed from each locality and brought it in our laboratory. Here, exactly 1000 seeds were randomly counted from each locality. This became our seed sample on which dissection was made. Dissection revealed further pests like: Megastigmus suspectus (in larval, pupal or imaginal stage), Resseliella piceae (larvae) and Earomyia impossibile (dead larvae or pupae). Of the mentioned insects only Resseliela and Megastigmus are regarded as true seminiphages. The rest of the pest impact was evaluated by visible biting marks or by remnants of their development stages (Earomyia). Aside from quantitative analysis, much of the collected material has been stored for further bioassay and this part of research is still going on.
Common spruce (Picea abies) and black pine (Pinus nigra) cone analysis was made in a similar manner. At central collecting site we randomly isolated certain quantities of unloaded cones and counted visibly attacked ones. On these two species another cone destroying species emerged as most often. Cydia strobillela was found in all spruce and pine collections. Pine cones were bearing exit holes from Pissodes validirostris but this insect does not appear to be of significant importance.