Eur. J. Entomol. 98: 433-438, 2001 ISSN 1210-5759 Diel changes in adipokinetic response and walking activity of Pyrrhocoris apterus (Heteroptera) in relation to physiological status and wing dimorphism Anna MAXOVÁ1-2, Dalibor KODRÍK1*2, Rostislav ZEMEK1and Radomír SOCHA1 institute ofEntomology, Academy of Sciences, Branišovská 31, České Budějovice, 370 05, Czech Republic 2Faculty ofBiological Sciences, University of South Bohemia, Branišovská 31, České Budějovice, 370 05, Czech Republic Key words. Pyrrhocoris apterus, Pya-AKH, adipokinetic response, walking activity, diurnal rhythm, diapause, wing polymorphism Abstract. Three experimental groups of adult females of Pyrrhocoris apterus (reproductive brachypterous, diapausing brachypter- ous, and macropterous with non-diapause type of reproductive arrest) were analysed for their dose dependency of adipokinetic response, sensitivity of the fat body to Pya-AKH and locomotor activity during a 24 hour cycle. The greatest adipokinetic response (lipid elevation after hormonal treatment) was observed in macropterous, lower in diapausing brachypterous and the lowest in repro ductive brachypterous females. Macropterous females also exhibited the highest activity of walking, while the lowest locomotor activity was found in diapausing brachypters. Diel changes of adipokinetic response were recorded in all three experimental groups, with maximal response occurring during the day at 6-7 h after the onset of light. On the contrary, the minimal adipokinetic response was found in the night and early after the onset of light. No significant differences in diel rhythms were observed between groups exposed to various day lengths. Diel changes in locomotor activity were found only in reproductive brachypterous females and females of macropterous morph, and showed a diurnal rhythm with only one peak of activity during a 24 hour cycle. In the latter, the rhythmic pattern of walking activity was positively correlated with diel changes of adipokinetic response. This indicates an impor tant role of Pya-AKH in dispersal strategy of macropterous females of this heteropteran. INTRODUCTION Adipokinetic hormone (AKH) is one of the best known neuropeptides that controls and regulates energy metabo lism in insects. Many AKHs have been isolated from cor pora cardiaca and characterized in a great number of insect orders (Gade et al., 1997; Gade, 1999; Lorenz et al., 1999), and recently also in the firebug Pyrrhocoris apterus, a representative species of the suborder Heterop tera (Kodrik et al., 2000). Almost all of these hormones are octa-, nona- or decapeptides with characteristic struc tural similarities (Gade et al., 1997), and they are grouped into the AKH/RPCH (Adipokinetic Hormone/Red Pig ment Concentrating Hormone) family. The first reported effect of AKHs was the lipid mobilization from the fat body of Locusta migratoria, which is known to provide an energy fuel for long term flight (Mayer & Candy, 1969). AKHs generally play an important role in stress situations, with the need for activation of energy stores. The stimulation of walking activity by AKH was recently proven in P. apterus (Socha et al., 1999a, b; Kodrik et al., 2000). P. apterus is a flightless species producing two major morphs, macropterous (long-winged) and brachypterous (short-winged). They differ, in addition to the length of the pre-oviposition period, in other physiological, bio chemical and behavioural parameters; e.g., the quantity of hexameric storage protein in haemolymph (Sula et al., 1995; Socha & Sula, 1996), feeding behaviour, digestive physiology, and glycogen and lipid content in the fat body (Socha et al., 1997, 1998). The differences in the life strategy of these morphs may be related to the flight capability of their macropterous ancestors. This presump tion is supported by the finding that, in spite of the loss of flight capability during evolution, the recent representa tives of the macropterous morph of P. apterus have retained wing flapping capability (Socha & Zemek, 2000a). Recent studies showed that the macropterous morph also differs from the brachypterous one by a more intensive response to AKH treatment (Kodrik & Socha, 1999; Socha & Kodrik, 1999) and by higher activity of walking (Socha & Zemek, 2000b). This finding suggests that AKH plays an important role in mobilization of lipid reserves from the fat body in the macropterous morph to energetically ensure their enhanced walking activity and higher tendency of dispersal. Recently, data on physiological and behavioural differ ences between reproductive and diapausing adults of P. apterus have been reported, for example differences in the amount of hexameric storage protein in the haemo lymph (Sula et al., 1995), adipokinetic response (Socha & Kodrik, 1999) and activity of walking (Socha & Zemek, 2000b). However, despite intensive research, our knowl edge of the relationships between diapause, lipid mobili zation and locomotor activity is still insufficient. A number of physiological and behavioural functions in insects related to certain concentrations of biomole cules are known to show rhythmic diurnal changes (Saun ders, 1982). Rhythms in the function of CNS and endocrine systems appear to play an important role in the control of various physiological and behavioural rhythms. AKH, as mentioned above, controls the release of lipids * Corresponding author: e-mail:kodrik@entu.cas.cz, fax: ++420-38-43625 433