EUROPEAN JOURNAL OF ENTOMOLOGYENTOMOLOGY ISSN (online): 1802-8829 Eur. J. Entomol. 116: 302–308, 2019 http://www.eje.cz doi: 10.14411/eje.2019.033 ORIGINAL ARTICLE Cannibalism among same-aged nymphs of the omnivorous predator Dicyphus errans (Hemiptera: Miridae) is affected by food availability and nymphal density KONSTANTINA ARVANITI 1, ARGYRO FANTINOU 2 and Dionyssios PERDIKIS 1 1 Laboratory of Agricultural Zoology & Entomology and 2 Laboratory of Ecology & Environmental Sciences, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Hellenic Republic; e-mails: [email protected], [email protected], [email protected] Key words. Hemiptera, Miridae, Dicyphus errans, adult weight, cannibalism, density, development, food availability, omnivorous predator Abstract. Cannibalism, the act of eating an individual of the same species has been little studied in omnivorous insect predators. Dicyphus errans (Wolff) (Hemiptera: Miridae) is a generalist omnivorous predator that commonly occurs in tomato greenhouses and fi eld crops in the Mediterranean basin. In this work cannibalism among same-aged neonate nymphs of D. errans was studied when 1, 2, 4, 8 or 16 individuals were placed in a Petri dish along with or without heterospecifi c prey. Although nymphs were un- able to complete their development in the absence of prey they survived longer when there were initially 2 individuals per dish than in any other treatment including a single individual. This may indicate that cannibalism in this predator has positive effect on nymphal survival, which however was not the case at higher densities. The presence of heterospecifi c prey increased nymphal survival and individuals were as equally successful in completing their development as when kept singly. Developmental time in all the treatments was very similar. Adult weight of both females and males was signifi cantly greater when a nymph was reared alone and similar in all the other treatments. The results indicate that cannibalism occurs among neonates of D. errans if heterospecifi c prey is scarce and has a negative effect on adult weight when heterospecifi c prey is abundant. This should be considered in stud- ies on enhancing the biocontrol effi ciency or mass rearing of this predator. INTRODUCTION of interacting conspecifi cs are also important drivers of Cannibalism, the process of killing and consuming a part cannibalistic behaviour resulting in (a) more cannibalism or all of a conspecifi c occurs in a wide range of carnivo- when the density of interacting conspecifi cs is high and rous as well as in phytophagous arthropods (Fox, 1975; (b) larger individuals being more effective cannibals than Polis, 1981; Woodward & Hildrew, 2002; Richardson et smaller ones (Fox, 1975; Polis, 1980, 1981; Dong & Polis, al., 2010; Booth et al., 2017). This behaviour may enhance 1992; Claessen et al., 2004; Reglero et al., 2011; Duan et fi tness of cannibals in periods of food scarcity by providing al., 2013; Parsons et al., 2013). Cannibalism is also infl u- them access to high quality nutrients, reducing competi- enced by the strength of intraspecifi c competition, mat- tion or decreasing the risk of predation and/or parasitism ing status, habitat structure and hunger level (Polis, 1981; (Fox, 1975; Polis, 1981; Gabriel, 1985; Van den Bosch et Wise, 2006). al., 1988; Agarwala & Dixon, 1992; Elgar & Crespi, 1992; Apart from mortality, cannibalism may have adverse ef- Henson, 1997; Gagné et al., 2002; Michaud, 2003; Claes- fects on life-history traits such as developmental rate or sen et al., 2004; Booth et al., 2017). Nevertheless, canni- weight gain (Fox, 1975; Polis, 1980; Lima, 1998). Studies balism may incur costs, including the risk of injuries from on phytophagous insects indicate that when immatures are conspecifi cs that fi ght back or the transmission of patho- abundant they grow slowly and are lighter as adults (Duan gens and parasites present in the victim attacked (Elgar & et al., 2013; Andow et al., 2015). The factors that affect Crespi, 1992). the intensity of these trait-mediated effects of cannibalism Various biotic and abiotic factors affect the incidence of and their implications at the population level are less well cannibalism in insect assemblages. The scarcity of alter- studied (Ruldof, 2007). native food is considered the most important factor pro- Omnivorous predatory insects are valuable biologi- moting cannibalism (Fox, 1975; Polis, 1981; Agarwala & cal control agents in tomato and other vegetable crops Dixon, 1992; Currie et al., 1996; George, 2002; Schaus- and are widely used commercially. Although interactions berger, 2003). Population density and population structure commonly occur among them such as those associated Final formatted article © Institute of Entomology, Biology Centre, Czech Academy of Sciences, České Budějovice. An Open Access article distributed under the Creative Commons (CC-BY) license (http://creativecommons.org/licenses/by/4.0/). 302 Arvaniti et al., Eur. J. Entomol. 116: 302–308, 2019 doi: 10.14411/eje.2019.033 with intraguild predation (Lucas et al., 2009; Moreno et and (b) presence of heterospecifi c prey. Our hypotheses al., 2012), the cannibalistic behaviour of only a few spe- were that a) the absence of heterospecifi c prey would result cies are documented (Tommasini et al., 2002; Laycock et in starvation, facilitate cannibalism and result in a higher al., 2006; Leon-Beck & Coll, 2007). Hamdi et al. (2013) survivorship of the cannibals and their achieving a greater show that females and males of Macrolophus pygmaeus size (Gabriel, 1985; Van den Bosch et al., 1988; Henson, (Rambur) (Hemiptera: Miridae) eat their own fi rst instar 1997), (b) the presence of heterospecifi c prey would result nymphs regardless of the availability of heterospecifi c in a lower incidence of cannibalism and (c) an abundance prey. Adult females of Dicyphus hesperus Knight (Hemip- of conspecifi cs would result in a greater incidence of can- tera: Miridae) attack and eat first and fourth instar nymphs nibalism. and male conspecifi cs (Laycock et al., 2006). Similarly, adult females or 4th instar nymphs of Dicyphus tamaninii MATERIALS AND METHODS Wagner (Hemi ptera: Miridae) also eat their own 1st instar Biological material nymphs (Castañé et al., 2002). Therefore, omnivores en- Rearing of D. errans was initiated from adults and late instar gage in size-related cannibalism. nymphs collected from Solanum nigrum L. (Solanaceae) at Kato Cannibalism has important consequences for the utili- Samiko, Ilia (W. Peloponnese, 37°54´41.05˝N, 21°59´92.57˝E, zation of omnivorous predators in biological control. For GPS). Insects were reared on potted tobacco plants (cv. Basmas) example, cannibalism can be an impediment to the mass and provided ad libitum with Ephestia kuehniella Zeller (Lepi- production of natural enemies (Riddick & Wu, 2010; De doptera: Pyralidae) eggs and dried Artemia sp. cysts (Crustaceae) (Entofood, Koppert B.V., The Netherlands) as food. Cultures of Clercq et al., 2013). As omnivores are also released early plants and D. errans were maintained in wood-framed entomo- in the cropping cycle, when heterospecifi c prey is usually logical cages (length 80 cm × width 80 cm × height 70 cm) and scarce, cannibalism may greatly reduce their abundance kept in an insectary at 25 ± 1°C, 65 ± 5% RH and a photoperiod and have a negative effect on their establishment (Calvo et of 16L : 8D. Tomato leaves used in experiments were collected al., 2012; Perdikis et al., 2015; Moerkens et al., 2017). In from 2-month old uninfested plants (cv. Elpida, Spirou House of addition, as they are usually released into crops as adults Agriculture, Athens, Greece) kept under the above conditions. their offspring can be abundant and, as a result, cannibal- Both tobacco and tomato plants were grown without applying ism is more likely to occur, which would adversely affect pesticides. their establishment. In fact, the effect of cannibalism is Experimental design dependent upon the timing of its occurrence, being more The experimental set-up consisted of plastic Petri dishes (Ø 9 pronounced when it occurs in early life as it has impor- cm, 1.5 cm height) with a mesh-covered hole in the lid (Ø 3 cm) tant consequences for survival, development, body size to reduce the level of humidity. A leafl et of a tomato plant was and reproduction (Ghazy et al., 2016). However not much placed, abaxial surface up, on a layer of water-moistened cotton is known about cannibalism among same-aged neonate on the bottom of each Petri dish. The petiole of the tomato leafl et nymphs. Since one of the major risks of being a cannibal was wrapped in absorbent cotton, which was soaked with water is being injured by the victim defending itself (Polis, 1981; daily. The leafl et was replaced with a new one every 2 days. In all experiments neonate nymphs (less than 24-h old) of D. errans Montserrat et al., 2006), the study of the cannibalism oc- were used. These were collected from individually caged tobacco curring between same-aged nymphs is challenging because plants with 6–8 fully expanded leaves. Ten adults of D. errans they may both injure each other (Fox, 1975; Polis, 1980). (5 females and 5 males) were introduced into each cage and they Under these circumstances the benefi ts of being a cannibal laid eggs in the stem of the plant. On the leaves of each plant E. or the factors affecting the intensity of cannibalism have to kuehniella eggs and cysts of Artemia sp. were added ad libitum as be assessed. Although such effects have important demo- prey for the adults. The plants in the cages were inspected every graphic and ecological effects on populations they are not 24 h and the freshly emerged nymphs were randomly assigned well studied (Rudolf, 2007). to each treatment. The cages were kept in a growth chamber at Dicyphus errans (Wolff) (Hemiptera: Miridae) is a gen- 25 ± 1°C, 65 ± 5% RH and a photoperiod of 16L : 8D.