Predators can significantly impact potential prey without consuming them, generating potential ramifications for biological control. In this study, we examined the cumulative impacts of adult Harmonia axyridis Pallas (Coleoptera: Coccinellidae) on development and reproduction of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), over three generations. Development became faster in each of the three generations and pupae became heavier than controls, although survival declined in the third generation. Predator stress increased wing deformations in the first generation, but not thereafter, and female fecundity became higher than controls in the third generation. We concluded that predator stress increased larval consumption to eventually result in both faster development and larger adult size when food was abundant. The results demonstrated that H. armigera could respond to exposure from a nonconsumptive predator by shifting aspects of developmental timing and increasing reproductive effort, with both individual-and population-level consequences. The adaptive significances of these changes are discussed. This study advances our understanding of the potential for non-lethal predators to impact prey life histories.

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

As larval cannibalism is common under intensive rearing conditions, leg regeneration can help ladybugs adapt to the competitive environment, but whether the leg regeneration leads to side effects on development remains unclear. To analyze the potentially developmental cost of leg regeneration, the developmental period and weight of leg-regenerated Coccinella septempunctata were studied in the laboratory. The results showed that, when the time intervals between the emergency of 4th-instar larva and leg amputation increased, the developmental period of leg-regenerated 4th-instar larvae was gradually prolonged. Significantly developmental delay were also examined at prepupal and pupal stages, and various timings of leg amputation affected the periods of leg-regenerated prepupae/pupae similarly. After the leg was amputated at different larval instars, the developmental delay only occurred at the larval instar when the leg was amputated, whereas other larval instars failed to be extended, and the developmental periods of leg-regenerated prepupae/pupae were affected similarly by the instars of leg amputation. Developmental delays possibly resulted in more consumption by leg-regenerated larvae, and then weight gains at prepupal/pupal stages, but different larval instars of leg amputation affected the weight gain similarly. Both the developmental delay (at 4th-instar larval, prepupal and pupal stages) and weight gain (at pupal and adult stages) in complete/bilateral amputation were longer or greater than those in half/unilateral amputation. However, the thoracic locations of leg amputation impacted the developmental delay and weight gain similarly. Our study indicates that although leg regeneration triggers the developmental cost decreasing the competitive superiority or agility, C. septempunctata larvae still choose to completely regenerate the leg to adapt to complex environments. Thus, in order to remain competitive at adult stages, leg-impaired larvae may make an investment tradeoff between leg regeneration and developmental cost.