ECOLOGICAL CHEMISTRY AND ENGINEERING A Vol. 15, No. 1 2 2008 Małgorzata KŁYŚ* EFFECT OF INCREASED TEMPERATURES ON THE POPULATION DYNAMICS OF SAW-TOOTHED GRAIN BEETLES Oryzaephilus surinamensis L. (Coleoptera, Cucujidae) ODDZIAŁYWANIE PODWYŻSZONYCH TEMPERATUR NA PROCESY POPULACYJNE SPICHRZELA SURYNAMSKIEGO Oryzaephilus surinamensis L. (Coleoptera, Cucujidae) Summary: The study included the saw-toothed grain beetles Oryzaephilus surinamensis L. kept in stores and granaries. The aim of the laboratory experiments was to analyse the effect of the short-termed and pe- riodically increased temperatures on the population dynamics of this species. The control and experimental cultures were kept in a thermostat at a temperature of 30 C and relative humidity (r.h.) of 70 %. Semolina was used as a substrate in all the cultures. In the first variant of the experiments, seven days before the assessment the cultures were exposed to a short-termed effect (0.5 h) of the temperature increased to 35 C. In the second variant, the cultures were exposed to the effect of the temperature increased to 35 C in the same way, but for 24 hours. It was found out that the increase in temperature, both short-term and periodical causes a decrease of a population size. The elevated temperature, especially lasting for 24 hours also causes an increase of the population mortality. Moreover, it was found out that the females are more sensitive to the effect of temperature rises. Keywords: Oryzaephilus surinamensis L., population dynamics, mortality, sex ratio The main factors which effect the rate of increasing pest populations living in closed granaries and stores are: food, temperature, humidity and a suitable amount of air [1, 2]. Extermination of store pests is onerous, mainly because to fight them we cannot use a large variety of chemical aids directly on the grain or stored groceries. Besides, the insects are characterized by a large migration activity [3, 4]. One of the possibilities to inhibit an increase in population is a suitable application of physical factors to create the least favourable conditions for this increase. A high effectiveness in killing some pests is acquired by applying sudden changes of temperature. This phenomenon is called a ther- mal shock [2]. * Department of Ecology, Wildlife Research and Ecotourism, Institute of Biology, Pedagogical University, Podbrzezie 3, 31-054 Kraków, email: klysgosia@poczta.onet.pl
76 Małgorzata Kłyś The aim of the presented studies was to analyse short-term and periodical effects of raised temperatures on the population dynamics of the saw-toothed grain beetles O. surinamensis. Materials and methods The experiments were carried out in thermostats at a temperature of 30 C and relative air humidity of 70 %. In the first variant of the experiment, the cultures were ex- posed to a short-term (0.5 h) effect of the temperature raised to 35 C every four weeks, seven day because the control. Then the vessels were put again in the temperature of 30 C in the second variant of the experiment. The cultures were subjected to the temperature raised to 35 C in the same way, but for 24 hours. The adult insects used for the experiments were 15 days old and came from the general cultures. Their sex was not determined assuming that the ratio of males to females in the same species is generally 1:1 and the exact determining of the sex worsens the condition of the individuals. All the experimental cultures were started with 40 adult individuals of the same age. Semolina, a convenient nutrient and habitat for a growth of the saw-toothed grain beetle, was used as a substrate. All the variants of the experiment was carried out six times. An effect of the raised temperatures on the population dynamics of O. surinamensis was assessed on the basis of analyzed parameters such as: size, mortality and sex structure of a population. The results were statistically analysed by the program Chi-square from Statistica v. 5.5 s. 999 FGPJI N4 was used. Results and discussion The obtained results show that a short-term, cyclic increase of temperature does not cause significant changes in the course of the population dynamics of O. surinamensis. The effect of the increased temperature is noticeable only in a slight decrease in the population size in comparison with the control culture, especially in the initial period of the experiments (Fig. 1). Mortality is maintaned on a low level until the 90 th day of the experiments, then is rises to 22 % (Fig. 2). However, it was not caused by the raised temperature, but as a result of the increasing population congestion and lack of food. The analysis of the sex ratio indicated that there is a constant dominance of the females in numbers both among the living and dead individuals except 100 th day when among the dead insectsan equal balance of the females and males was observed (Fig. 3). In spite of the fact that O. surinamensis belongs to stenothermic species [2], longer, a 24 h increase in temperature disturbs population processes. As a result, the maximum of population sizes was found a month earlier and the size in particular periods of time was much lower in comparison with the size in the control culture. The total size was also considerably lower (Fig. 1). The data, analysed with the Chi-square show that the differences of sizes between the control population and the population subjected to a 24 h rise in temperature are statistically significant in every time interval. Twenty-four hour cyclic rises in temperature caused, in comparison with thirty minute exposure at the
Effect of Increased Temperatures on the Population Dynamics of Saw-Toothed Grain Beetles... 77 Fig. 1. Comparision of population dynamics of Oryzaephilus surinamensis in different temperature conditions Fig. 2. Per cent of dead individuals in populations of Oryzaephilus surinamensis in different temperature conditions
78 Małgorzata Kłyś Fig. 3. Comparision of sex ratios in Oryzaephilus surinamensis in diffrent temperature conditions (individuals live) Fig. 4. Comparision of sex ratios in Oryzaephilus surinamensis in different temperature conditions (individuals dead)
Effect of Increased Temperatures on the Population Dynamics of Saw-Toothed Grain Beetles... 79 same temperature, a significant increase in mortality during the whole period of the ex- periments. The mortality rate fluctuates fron 14 to 48 % (Fig. 2). The sex rate was lower than 1 during the whole time which indicates a majority of females in the population (Fig. 3). The lowest sex rate was noted among the dead individuals (Fig. 4). This points to higher mortality among females. As a result of such population processes, a gradual limitation of a population increase takes place. Gołębiowska et al. [5] found out, in their studies on the effect of temperature and relative humidity of air on feeding intensity and location of damage caused by grana- ry beetles on wheat, rye and corn grains, thot the most intensive feeding was in the temperatures ranging from 23 to 26 C. Sandner [6] found, too, that short-term changes of temperature and humidity produced a definite effect on the appearance the next gen- eration of granary beetles. Apart from other factors, temperature is responsible for distribution and occupation of new habitats by rice weevil Sitophilus oryzae L., lesser grain borer Rhizopertha dominica F. and saw-toothed grain beetle Oryzaephilus surinamensis L. Hardman [8], Cuff and Hardman [9] examined the effect of temperature, humidity of the grain and the speed of laying eggs on the population size of S. oryzae in the stored wheat in granaries. The obtained results served for working out models which gave a basis to assess the effect of low temperatures and humidity on the decrease of the insect population sizes in wheat which was kept in closely tight places. These results are an example of forecasting modelling based on well-known effects of combining biotic and abiotic factors. Conclusions: 1. An increase in temperature both short-term and periodical causes a decrease in a population size. 2. A higher temperature lasting for 24 h causes an increase in population mortality 3. Females are more sensitive to temperature rises. References [1] Chang S. S. and Loschiavo S. R.: The influence of some fungi in flour and humidity on the survival and development of Cryptolestes turcicus (Col. Cucujidae).. Can. Ent., 1971, 18,, 261 266. [2] Nawrot J.: Owady Szkodniki Magazynowe, Wyd. Themar, Warszawa 2002. [3] Ciesielska Z. and Kłyś M.: Aktywność migracyjna populacji kapturnika zbożowca Rhyzopertha domi- nica F. (Coleoptera, Bostrychidae).. Ann. Acad. Paedag. Cracov., 2002, (7), 25 37. [4] Kłyś M.: Correlation between nutritional selectivity and migratory activity of Rhizopertha dominica F. (Coleoptera, Bostrichidae). J. Plant Protect. Res., 2006, 4,, 369 378. [5] Gołębiowska Z., Prądzyńska A. and Nawrot J.: Lokalizacja i wpływ uszkodzeń powodowanych przez chrząszcze na ziarnie zbóż na kiełkowanie i wzrost roślin.. Zesz. Probl. Post. Nauk Roln., 1978, (202), 155 171. [6] Sandner H.: Wpływ pokarmu środowiska na populacje niektórych owadów.. Ekol. Pol., 1968, 3,, 235 255. [7] Yinon U. and Shulov A.: The dispersion of trogoderma granarium in a temperature gradient and com- parison with other stored product beetles.. Ent. Exp. Appl., 1970, 13,, 107 121. [8] Hardman J. M.: A logist model simulating environmental changes associated with the growth of popula- tions of rice weevils, Sitophilus oryzae, reared in small cells of wheat. J. Appl. Ecol., 1978, 15,, 65 87.
80 Małgorzata Kłyś [9] Cuff W. R. and Hardman J. M.: A development of the Leslie matrix formulation for restructuring and extending an ecosystem model: The infestation of stored wheat by Sitophilus oryzae.. Ecol. Modelling 1980, 9,, 281 305. ODDZIAŁYWANIE PODWYŻSZONYCH TEMPERATUR NA PROCESY POPULACYJNE SPICHRZELA SURYNAMSKIEGO Oryzaephilus surinamensis L. (Coleoptera, Cucujidae) Streszczenie z e e Badaniami objęto spichrzela surynamskiego Oryzaephilus surinamensis L. owada żyjącego w produk- tach zbożowych przechowywanych w magazynach i spichlerzach. Celem badań laboratoryjnych była analiza wpływu krótkotrwałego i okresowego działania podwyższo- nych temperatur na przebieg procesów populacyjnych tego gatunku. Hodowle kontrolne i eksperymentalne prowadzono w termostacie w temperaturze 30 C i wilgotności względnej 70 %. Jako substrat we wszystkich hodowlach zastosowano kaszę mannę. W pierwszym wariancie eksperymentu hodowle co cztery tygodnie, siedem dni przed terminem kontroli, poddawano krótkotrwałemu (0,5 godz.) oddziaływaniu podwyższonej do 35 C temperatury. W drugim wariancie eksperymentu hodowle poddawano w taki sam sposób oddziaływaniu temperatury podwyższonej do 35 C, ale przez okres 24 godzin. Stwierdzono, że podwyższenie temperatury zarówno krótkotrwałe, jak i okresowe powoduje zmniejszenie liczebności populacji. Podwyższona temperatura, zwłaszcza działająca przez okresy 24-godzinne powoduje także wzrost śmiertelności populacji. Ponadto stwierdzono, że samice są bardziej wrażliwe na podwyższanie temperatury. Słowa kluczowe: spichrzel surynamski, dynamika liczebności populacji, śmiertelność, wskaźnik płci