Researches on the ecology and biology of Eurygaster integriceps Put. (Hemiptera, Scutelleridae) in Middle East countries, with special reference to the overwintering period

Abstract

Three years of research on Eurygaster integriceps Put., and other Pentatomoids associated with cultivated cereals in Middle East countries, covered many aspects of the biology and control of these insects. This report is concerned especially with the overwintering or resting period and certain aspects of the annual life-cycle and physiology of E. integriceps.Up to now these aspects have been studied mainly in the U.S.S.R., and frequent reference has been made to this work. The main objective in the author's own research has been not to explore fresh fields but rather to ascertain whether conclusions reached by workers in Russia are applicable also in countries of the Middle East.Typically, E. integriceps spends a relatively short active period in the cereal fields in spring and early summer, and the young adults of the new generation migrate in mid-summer to higher altitudes in the mountains, where they spend a few autumn months in aestivation, followed by a hibernation period during the cold months of late winter; they descend to the fields again in spring. A number of different overwintering areas were visited in Turkey, Iraq and Iran, and two were selected for special long-term studies; one was Karacadag mountain, near Diyarbakir in south-east Turkey, and the other Ghara-agadj mountain, in the Varamine district near Tehran, in Iran.Some of the ecological characters of these areas were studied, including the vegetation and certain climatic factors; the latter included maximum and minimum temperatures and relative humidity, and were studied more intensively on Ghara-agadj. Special attention was given to the microclimatic conditions under the plants where the insects are actually situated.Population density has been studied at observation stations at different altitudes in the overwintering areas. Two methods are described for estimating population density in terms of the number of insects per square metre. Certain plants are more suitable for shelter than others, and there is some evidence that different types of plants tend to be used more extensively for shelter in the aestivation and hibernation periods. The distribution of these plants affects local variations in population density.Monthly estimates of density at different altitudes confirmed that there is a partial downward autumn migration which takes place in October on both Ghara-agadj and Karacadağ. Mortality was also estimated during these counts and found to be highest after aestivation, and to affect males more than females. This differential mortality, and also a difference in migratory behaviour between the sexes, brings about differences in the proportions of males and females at different times and in different places; an account has been given of the changes, both local and over-all, in sex ratio throughout the year, and in most cases the reasons for them can be understood.Research has been carried out on certain aspects of the physiology of Eurygaster, with particular reference to the fat content and the condition of the internal organs (‘ morphofunctional condition ’) and the seasonal changes which they undergo during the year. Fat content has been extensively estimated by chemical analysis, and morphofunctional condition by dissection. The Russian method of forecasting the strength of invasions by reference to physiological condition is discussed; analysis of population changes on Ghara-agadj (where numbers were increasing) and on Karacadağ (where numbers were decreasing) suggests that the present work supports this system of forecasting in principle, provided it is maintained for long periods and the condition of the population kept under regular observation. Fat analysis has proved a more reliable method than dissection for assessing the physiological condition of the population. This condition is not in itself an adequate criterion for making forecasts, and a summary is given of other factors determining the future population density which should be taken into account.