Optimisation of a semiochemical slow-release alginate formulation attractive towards Aphidius ervi Haliday parasitoids

BACKGROUND: Optimisation of alginate formulations is described in order to develop semiochemical (E-β-farnesene and
E-β-caryophyllene) slow-release devices in biological control approaches by attracting predators and parasitoids of aphids.
Various formulation criteria were optimised with respect to semiochemical encapsulation capacity. Moreover, the optimised
formulation was characterised by texturometry and confocal microscopy. The slow-release rates of semiochemicals were
calculated in laboratory controlled conditions. The attractiveness of semiochemical formulations towards Aphidius ervi was
demonstrated by olfactometry.
RESULTS: Two major parameters were highlighted in encapsulation optimisation: the type of alginate (Sigma L) and the type
of crosslinker ion (Ca2+). Other formulation parameters were optimised: ionic strength (0.5M), Ca2+ (0.2 M) and alginate
(1.5%) concentrations and the maturation time of beads in CaCl2 solution (48 h). After physical characterisation of beads,
semiochemical slow-release measurements showed that alginate formulations were efficient sesquiterpene releasers, with
503 μg of E-β-farnesene and 1791 μg of E-β-caryophyllene totally released in 35 days. The efficiency of semiochemical alginate
beads as attractants for female parasitoids was demonstrated, with high percentages of attraction for semiochemical odours
(88 and 90% for E-β-farnesene and E-β-caryophyllene respectively) and significant statistical results.
CONCLUSION: Semiochemical alginate beads can be considered as efficient slow-release systems in biological control. These
formulations could be very useful to attract aphid parasitoids on crop fields.