Prospective generalist invertebrate predators for conservation biological control of the vineyard pests Epiphyas postvittana and Pseudococcus calceolariae

Abstract

A series of field surveys and experiments were performed to identify generalist invertebrate predators which could complement the parasitoid Dolichogendia tasmanica in management of the vineyard pest Epiphyas postvittana and an additional pest Pseudococcus calceolariae.

Conventional agricultural methods have been able to improve food production but some practices have been at the cost of ecosystem services, and beneficial services derived from the ecosystem. A dependence on agro-chemicals to maintain production can develop in order to substitute for services that have been lost, threatening the long-term sustainability of production. Biological control is one of these ecosystem services which can be employed in place of chemical pesticide inputs and, with prudent investigation, can maintain productivity and improve sustainability.

Conservation biological control (CBC) is a form of biological control that utilises natural enemies from within the ecosystem, circumventing some of the issues traditionally associated introducing a new species with classical and augmentative biological control. Another advantage of CBC is that generalist natural enemies are potentially more acceptable to include in pest management. Traditionally, generalists have been deemed unsuitable in biological control but there could be potential as an early-season management tool to complement existing E. postvittana biological control in vineyards with D. tasmanica. Additionally, there may be an advantage of generalist predators attacking a second vineyard pest, Ps. calceolariae.

To begin to identify those generalist natural enemies that may be incorporated in vineyard pest management, predator surveys of the ground and canopy of twelve organic and conventional vineyards were carried out from 2010 to 2012 in Marlborough, New Zealand. Sentinel bait cards with E. postvittana larvae or eggs were placed throughout the vineyards and the predator species attacking the pest and comparative removal rates were observed. To determine which vineyard predators of E. postvittana could attack both pest species, maximum consumption rate experiments with E. postvittana larvae and eggs, along with adult females and nymphs of Ps. calceolariae, were carried out in laboratory arenas.

Subsequently, experiments were carried out in vine canopy cages to investigate interactions between the predator species and the prey preferences of predator species. Individuals of each predator species that attacked both pest species in laboratory experiments were presented with a pairwise choice of Ps. calceolariae nymphs and E. postvittana larvae or eggs to test for any prey preference by the predator species. In experiments examining inter-specific predator interactions, each combination of predator species was presented with the different prey types where a variation from the null hypothesis indicated non-linear relationships (antagonism or synergism).

Three predator species were observed attacking E. postvittana eggs and larvae on bait cards in the vineyard canopy; Anystis baccarum, Forficula auricularia, and Phalangium opilio. Functional predator diversity was higher in organic vineyards, but no difference in prey removal rates of E. postvittana eggs or larvae between conventional and organic vineyards was observed. In laboratory trials, F. auricularia killed more of each prey type than the two other predator species, and was the only predator species to predate on all prey types of both pest species. P. opilio consumed both E. postvittana prey types plus Ps. calceolariae nymphs. Although A.baccarum consumed only E. postvittana eggs in laboratory trials, despite attacking larvae on bait cards in the vineyards, their consumption rate was not significantly different from that by P. opilio. Only F. auricularia and P. opilio were used in prey preference experiments, as A. baccarum consumed only one prey type in the laboratory. F. auricularia showed no preference between Ps. calceolariae nymphs, E. postvittana larvae or eggs; however P. opilio did display a preference for E. postvittana eggs over larvae but no preference between pest species was observed. When all three predators were combined as an assemblage, a consistent additive effect on predation across Ps. calceolariae nymphs, E. postvittana larvae and eggs was observed. F. auricularia interacted antagonistically when combined with either of the alternative predator species and presented with E. postvittana eggs, and again with the predator P. opilio and Ps. calceolariae nymphs as prey. E. postvittana larvae predation was higher than hypothesised in both pairwise predator combinations that included A. baccarum. Not one of the three predator species identified as potential CBC agents of E. postvittana in vineyards can be ruled out, but a range of potential strengths and limitations was identified. F. auricularia predated on all pest prey that was presented, and consumed more of each prey type than the other predator species. However, the negative interactions with the alternative predators could diminish improvements to pest control gained by promoting this species for biological control. A. baccarum had the most limited range of prey but was the most frequently observed attacking E. postvittana in vineyards and could be effective mitigating non-additive interactions between other predators’, including prey which this predator was not observed predating on. The preference of P. opilio for E. postvittana eggs over larvae indicates potential complementarity with D. tasmanica, a larval parasitoid, as overlap in prey use could be reduced. While P. opilio was, comparatively, not a voracious predator of the pest species, it did predate on both species.

The observations made here can be used to progress investigations of these predator species as CBC agents. How these candidates perform and interact with other species in unrestricted vineyard systems and the nature of interactions with the E. postvittana parasitoid D. tasmanica are two key areas to pursue. The final outcome will be developing practices that provide service providing units (SPU) for managing E. postvittana and Ps. calceolariae that improves crop yield and quality. There was evidence that A. baccarum, F. auricularia, and P. opilio can potentially complement D. tasmanica to this effect.