Role of surface chemical signals in egg cannibalism and intraguild predation in ladybirds (Coleoptera: Coccinellidae)

Abstract

Summary. The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the surface of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony.

Effects of mass releases of Trichogramma brassicae on predatory insects in maize

“…This finding is in line with the observation that the alkaloids of A. bipunctata are less toxic than those of C. septempunctata (De Jong et al, 1991). Recently, Hemptinne et al (2000) noted that such a defence is of little value if the eggs are killed before their toxicity becomes apparent. Our own direct observations, however, suggest that the toxicity of coccinellid eggs becomes apparent early enough for T. brassicae females to lead to a low probability of parasitisation under field conditions.…”

“…Thus far, few egg parasitoids have been reared from coccinellids and these scarce records did not include Trichogramma (Hodek & Honek, 1996). The reason may be that eggs, like other stages of coccinellids, are chemically defended (e.g., Agarwala & Dixon, 1992;Hemptinne et al, 2000). Our results indicate that the eggs of A. bipunctata are less deterrent to T. brassicae than eggs of C. septempunctata.…”

Effect of presence and semiochemicals of conspecific stages on oviposition by ladybirds (Coleoptera: Coccinellidae)

“…Soares & Serpa (2006) have observed no oviposition in Coccinella undecimpunctata L. in the presence of adult H. axyridis, but the reverse in case of conspecific adults. Females of C. sexmaculata are known to lay fewer eggs in the presence of an immobilized conspecific adult female (Agarwala et al, 2003), whereas C. septempunctata does not oviposit in the presence of conspecific adult females (Hemptinne et al, 1993). Mishra & Omkar (2006) have also shown inhibitory effects of female conspecific presence and semiochemicals in P. dissecta.…”

“…Only a few studies discuss the role of egg (Hemptinne & Dixon, 1991;Hemptinne et al, 1993), pupal (Hemptinne & Dixon, 1991) or adult presence (Hemptinne et al, 1992(Hemptinne et al, , 1993Mishra & Omkar, 2006) and/or their semiochemicals in influencing oviposition (Doumbia et al, 1998;Mishra & Omkar, 2006). Previous studies have found no influence of egg and pupal presence on oviposition (Hemptinne & Dixon, 1991;Hemptinne et al, 1993). Adult ladybirds known to leave tracks include Epilachna vigintioctomaculata, Epilachna vigintioctopunctata (Fabricius) and C. septempunctata (Kosaki & Yamaoka, 1996;Nakashima et al, 2004).…”

“…Thereafter, the oviposition deterring effects of larval tracks have been identified in a number of ladybirds (R ži ka, 1997, 2001a, b, 2002, 2003, 2006Yasuda et al, 2000) and that of adult tracks in Propylea dissecta (Mulsant) (Mishra & Omkar, 2006). The effect of oviposition deterring pheromone (ODP) has been most intensively studied in coccinellids but in such arenas that allowed contact with conspecific females, a situation that has been shown to affect oviposition behavior in aphid parasitoids (Michaud & Mackauer, 1995) and coccinellids (Hemptinne et al, 1993;Mishra & Omkar, 2006), with an increased incident of superparasitism being observed in the former. To account for the possibly important influences of prey, host plant and conspecific interference, Yasuda et al (2000) and Michaud & Jyoti (2007) studied oviposition responses by solitary females to larval tracks in Harmonia axyridis (Pallas) and Coccinella septempunctata Linnaeus, and Hippodamia convergens Guerin respectively, in the presence of host plants and aphids.…”