Intraguild Predation Responses in Two Aphidophagous Coccinellids Identify Differences among Juvenile Stages and Aphid Densities

Abstract

(1) Intraguild predation (IGP) can occur among aphidophagous predators thus reducing their effectiveness in controlling crop pests. Among ladybirds, Coccinella septempunctata L. and Hippodamia variegata Goeze are the most effective predators upon Aphis gossypii Glov., which is an economically important pest of melon. Understanding their likelihood to engage in reciprocal predation is a key point for conservation of biological control. Here, we aim to investigate, under laboratory conditions, the level of IGP between the two above mentioned aphidophagous species. (2) Fourth-instars of the two species were isolated in petri dishes with combinations of different stages of the heterospecific ladybird and different densities of A. gossypii. The occurrence of IGP events was recorded after six hours. (3) C. septempunctata predated H. variegata at a higher rate than vice versa (70% vs. 43% overall). Higher density of the aphid or older juvenile stage of the IG-prey (22% of fourth instars vs. 74% of eggs and second instars) reduces the likelihood of predation. (4) To our knowledge, IGP between C. septempunctata and H. variegata was investigated for the first time. Results represent a baseline, necessary to predict the likelihood of IGP occurrence in the field.

Molecular detection of field predation among larvae of two ladybird beetles is partially predicted from laboratory experiments

“…variegata , although when correcting the raw data it seemed that C . septempunctata might be a superior IG-predator, apparently confirming the asymmetrical IGP detected in Petri dish experiments 33 . However, when observed vs. expected data were compared, still the field observed IGP by C .…”

“…septempunctata predated upon H . variegata at a higher rate than vice-versa (70% vs. 43% overall) and the likelihood of IGP was reduced at higher aphid densities or older juvenile stages of the IG-prey (22% upon fourth instars vs. 74% upon eggs and second instars) 33 . Similarly, C .…”

“…In addition, we aimed at developing a method that allows comparing IGP levels obtained under laboratory conditions (row data from ref. 33 ) with results from field-collected larvae. Molecular data typically consist in several positive or negative outcomes and it is not easy to straightforwardly derive ecological significance 28 .…”

“…Ladybirds, mostly Coccinella septempunctata L. and Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), are considered important and efficient naturally occurring predators of A . gossypii 32 , but since they are euryphagous in their diet breadth, it is predicted that they are likely to engage in IGP 33 .…”

Cannibalistic behavior of aphidophagous coccinellid, Hippodamia variegata (Goeze, 1777) (Coleoptera: Coccinellidae)

“…The phenomenon of egg cannibalism in ladybirds, including H. variegata, has also been regarded as a mean of nutritional and energetic gains in term of larger body size, faster development, earlier maturity, competitive advantage in mating and higher rate of reproduction (Osawa, 1992;Felix & Soares, 2004;Michaud & Grant, 2004;Omkar et al, 2004;Pell et al, 2008;Rondoni et al, 2014). Poor diet quality also exerts pressure on predators to feed on their conspecifics.…”