Behavioral responses of Diabrotica adults to plant-derived semiochemicals encapsulated in a starch borate matrix

The concept of encapsulating semiochemicals into a starch matrix is being studied for potential use in corn rootworm (CRW) management programs. During 1987, experiments were conducted to determine: 1) If volatile plant-derived Diabrotica spp. attractants could be encapsulated in a starch borate matrix (SBM), and 2) If various SBM-semiochemical formulations would attract Diabrotica species over time in field corn. Chemical analyses of fresh SBM formulations indicated that indole, estragole, veratrole, phenylacetaldehyde, and trans-anethole were not retained during formulation but trans-cinnamaldehyde, Beta-ionone, 1,2,4,-trimethoxybenzene, eugenol and isœugenol were successfully encapsulated. Encapsulated semiochemical formulations were made into 20 mesh granules, placed in Pherocon ® 1C traps that were tied to corn plants, and sampled for CRW adults every 4 days from 11 July to 8 September. Field data indicated that encapsulated semiochemicals were retained in the SBM for varying lengths of time and were released at rates attractive to CRW adults. A two-component mixture of trans-cinnamaldehyde and 1,2,4-trimethoxybenzene was the most effective formulation tested; however, no formulation was effective during corn silking and pollination. Although seasonal variation in CRW response could limit the usefulness of some plant-derived semiochemicals, the starch matrix concept may be useful as a delivery system for semiochemicals and may have potential as a tool that could be used in the development of new more biorational CRW management programs. RESUME Reactions comportementales d'adultes de Diabrotica a des substances allelochimiques d'origine vegetale encapsulees dans de l'amidon additionne d'acide borique Le programme experimental de 1987 etait destine a determiner: 1) si les substances derivees de vegetaux et attractives pour Diabrotica pouvaient etre encapsulees dans de l'amidon additionne d'acide borique; 2) si differentes formules attireraient les differentes especes de Diabrotica dans un champ de mais. L'indol, l'estragol, le veratrol, le phenylacetaldehyde et le trans-anethol n'ont pas ete retenus, tandis que le trans-cinnamaldehyde, la β-ionone, le 1,2,4-trimethobenzene, l'eugenol et l'isœugenol ont ete encapsules avec succes dans des pieges attaches a des pieds de mais (les details techniques sont fournis). Les pieges ont ete releves tous les 4 jours du 11 juillet au 8 septembre. Les resultats montrent que les substances allelochimiques sont conservees dans la capsule pendant des durees variables et liberees a des concentrations attractives pour les Diabrotica adultes. Un melange de trans-cinnamaldehyde et de 1,2,4,-trimethoxybenzene a ete la formule la plus efficace, a l'exception des periodes de formation des barbes et du pollen, ou aucune formule n'a ete attractive. Bien que la variation saisonniere des reactions de Diabrotica limite l'utilisation des substances allelochimiques d'origine vegetale, la capsule d'amidon peut etre employee pour liberer des substances allelochimiques et constitue un outil potentiel pour la mise au point d'une methode plus rationnelle de lutte contre Diabrotica.