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Two species of leaf beetle (Oulema spp.) – Oulema melanopus (Linnaeus 1758) and Oulema gallaeciana (Heyden 1870) are classified as the pests of cereals of economicalimportance in Poland. Determination of the optimalperiod of their control is very difficult due to extended time of laying eggs and brood of larvae. Mass brood of larvae of both species takes place at the time when larvae hatched from first laid eggs reached ca. 4 mm length of both species. Both developmental stages indicate an optimal term of leaf beetle control. To improve short-term forecasting and warning system the data on developmental cycles of both species from an egg to larva (ca. 4 mm size), the studies were carried out in the field trails in the Wielkopolska region and some in an environmental growth chamber.
The oats were observed to be the species mostly damaged by Oulema ssp. phytophages which is represented by the highest damage indexes of the plant in all the objects researched. The two other species: barley and spring triticale are much less sensitive to feeding of the pest. The initial damage which was due to the complementary feeding was hidden due to the compensation capabilities of the cereals. Spring barley, which tillers most, compensated for the damage most considerably. The economic harmfulness of the Oulema feeding may be estimated only in shooting phase, when also the larvae start skeleting of leaf blades. In barley and spring triticale a considerably lower larvae feeding was observed when compared with leaf beetles. The co-ordinate cultivation of the researched species with fodder pea and in two-ingredient cereal mixtures enhances the damage reduction caused by Oulema feeding.
The cereal leaf beetles Oulema melanopus L. and Oulema gallaeciana Heyden (Chrysomelidae) are common pests in European and North American cereal fields. Here we report infestation rates by Oulema spp. and yield loss of winter wheat and barley in Northern Poland (1995 to 1997) and show that both Oulema species might be of significant economic importance. Oulema melanopus was in all the three study years more abundant than Oulema gallaeciana. Larval densities ranged from 22 to 26 larvae per 100 stalks for winter wheat and 29 to 36 larvae per 100 stalks for barley. From these data we estimate yield losses of 0.5 to 4% for winter wheat and 3 to 8% for barley. The significant negative correlation between beetle abundances and the hydrothermic index indicates that higher precipitation and/or lower temperature had a negative effect on the activity of O. melanopus and O. gallaeciana.
Two species of leaf beetles from Chrysomelidae family i.e. the cereal leaf beetle Oulema melanopus (Linnaeus 1758) and the blue leaf beetle Oulema gallaeciana (Heyden 1970) can cause considerable damage to cereal crops. Improvement of short-term forecasting was focused on determination of optimal time of control of these pests that takes place at mass larval hatching. Thus long term studies were carried out to evaluate a correlation between duration of egg incubation, temperature and air humidity. The length of egg incubation was examined at temperatures of 16°C, 20°C and 25°C and air humidity 60% in a growth chamber and under field conditions. Based on linear and curvilinear multinomial regression analyses the influence and significance of such independent variable (x) as: sum of temperatures (sums of mean daily temperatures), mean air humidity, sum of effective temperatures and mean effective temperature versus duration of egg incubation of O. melanopus and O. gallaeciana (dependent variable – y) were evaluated. Analyses of 32 interactions (x, y) showed that only four were insignificant i.e. mean air humidity in the growth chamber at 20°C had no effect on the length of egg incubation of O. melanopus and at 25°C on the length of egg incubation of O. gallaeciana. Also under field conditions sums of effective temperatures showed no effect on duration of egg incubation of both species.
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