Intraspecific alkaloid variation in ladybird eggs and its effects on con- and hetero-specific intraguild predators

Abstract

Egg predation and cannibalism are common phenomena in predatory ladybirds despite the presence of defensive alkaloids. Consumption of heterospecific eggs negatively affects survivorship and development; however, intraspecific variation in quantities of alkaloids and post-ingestion responses to con- and hetero-specific alkaloids, are not well understood. We examined variation in the quantity of alkaloids in eggs of Harmonia axyridis (Pallas), Coccinella septempunctata L., and Hippodamia convergens (Guérin) using gas chromatography-mass spectrometry, and show a link between heterospecific alkaloids and their toxicity and/or costs by feeding high and low alkaloid eggs to first instar H. axyridis and C. septempunctata. The repeatability of alkaloid measurements in eggs in an egg cluster was high; however, the amount of alkaloids varied significantly between egg clutches within and among females. This variation affected egg consumption by C. septempunctata when fed H. axyridis eggs. Harmonia axyridis accumulated their own alkaloid by cannibalism and synthesized it de novo, but C. septempunctata lost some portion of the consumed conspecific alkaloids. Both species lost most of the consumed heterospecific alkaloids, but C. septempunctata died within 3 days. Most H. axyridis survived to the second instar, but C. septempunctata alkaloids led to a significant reduction in weight gain compared to an aphid control. In addition, ingestion of high alkaloid C. septempunctata extended development of H. axyridis compared to the aphid control or conspecific eggs. Harmonia axyridis had greater abilities to process ingested con- and hetero-specific alkaloids compared with C. septempunctata, which may, in part, explain their interspecific interactions in nature.

Stage specific consumption and utilization of aphids, conspecific and heterospecific eggs by two species of Coccinella (Coleoptera: Coccinellidae)

“…In addition, the ladybirds studied may utilize the nutrients in aphids with greater efficiency than those in con-or heterospecific eggs, which could also result in larvae taking less time to develop and bigger adults. The results are in agreement with many previous studies (Sato & Dixon, 2004;Cottrell, 2007;Sloggett et al, 2009;Kajita et al, 2010;Hemptinne et al, 2011). Further, because of its higher consumption rates, conversion efficiencies and growth rates the immature stages of C. septempunctata developed faster and the adults were bigger when fed on aphid or eggs than were those of C. transversalis.…”

Behavioral and Immunological Features Promoting the Invasive Performance of the Harlequin Ladybird Harmonia axyridis

“…As mentioned above, intraguild predation among predatory ladybirds may explain why H. axyridis can successfully outcompete native ladybirds (Gardiner et al, 2011). For example, A. bipunctata beetles die when feeding on H. axyridis eggs or larvae, but H. axyridis beetles suffer no ill effects when the relationship is reversed (Kajita et al, 2010). Accordingly, we found that microsporidia associated with H. axyridis kill A. bipunctata adults feeding on H. axyridis eggs (Vogel et al, 2017a).…”

Predators and parasitoids of the harlequin ladybird, Harmonia axyridis, in its native range and invaded areas

“…Many laboratory assays indicate its higher toxicity and/or unpalatability compared to other members of aphidophagous guilds (ladybirds, lacewings) (Phoofolo and Obrycki 1998;Cottrell 2004;Sato and Dixon 2004;Kajita et al 2010;Nedvȇd et al 2010). Further protection of the larvae is provided by spiny projections on their cuticle.…”