Impact of the dual defence system of Plantago lanceolata (Plantaginaceae) on performance, nutrient utilisation and feeding choice behaviour of Amata mogadorensis larvae (Lepidoptera, Erebidae).

Iridoid glycosides are plant defence compounds with potentially detrimental effects on non-adapted herbivores. Some plant species possess ß-glucosidases that hydrolyse iridoid glycosides and thereby release protein-denaturing aglycones. To test the hypothesis that iridoid glycosides and plant ß-glucosidases form a dual defence system, we used Plantago lanceolata and a polyphagous caterpillar species. To analyse the impact of leaf-age dependent differences in iridoid glycoside concentrations and ß-glucosidase activities on insect performance, old or young leaves were freeze-dried and incorporated into artificial diets or were provided freshly to the larvae. We determined larval consumption rates and the amounts of assimilated nitrogen. Furthermore, we quantified ß-glucosidase activities in artificial diets and fresh leaves and the amount of iridoid glycosides that larvae feeding on fresh leaves ingested and excreted. Compared to fresh leaves, caterpillars grew faster on artificial diets, on which larval weight gain correlated positively to the absorbed amount of nitrogen. When feeding fresh young leaves, larvae even lost weight and excreted only minute proportions of the ingested iridoid glycosides intact with the faeces, indicating that the hydrolysis of these compounds might have interfered with nitrogen assimilation and impaired larval growth. To disentangle physiological effects from deterrent effects of iridoid glycosides, we performed dual choice feeding assays. Young leaves, their methanolic extracts and pure catalpol reduced larval feeding in comparison to the respective controls, while aucubin had no effect on larval consumption. We conclude that the dual defence system of P. lanceolata consisting of iridoid glycosides and ß-glucosidases interferes with the nutrient utilisation via the hydrolysis of iridoid glycosides and also mediates larval feeding behaviour in a concentration- and substance-specific manner.

Safety evaluation of beta-glucanase derived from Trichoderma reesei: summary of toxicological data.

Barlican, a beta-glucanase enzyme obtained from Trichoderma reesei, was produced by a fermentation process and subjected to a series of toxicological tests to document its safety for use as a feed additive. The enzyme product was examined for general oral toxicity, inhalation toxicity, irritation to eye and skin, skin sensitization and mutagenic potential. An extensive literature search on the production organism was also conducted. Furthermore, safety for target species was assessed in a 28-day oral toxicity study with broilers. A strong skin-sensitizing potential of the beta-glucanase enzyme was detected, but no other evidence of oral or inhalation toxicity, mutagenic potential, eye or skin irritancy was found. Feeding of the beta-glucanase enzyme at dietary levels up to 10,000 ppm in the 90-day subchronic toxicity study in rats did not induce noticeable signs of toxicity. In addition, no adverse effects were observed when broiler chicks were fed dietary concentrations of the beta-glucanase enzyme up to eight times the daily recommended dose. It is therefore concluded that this beta-glucanase preparation is safe for use in feed of the intended target species. However, some occupational health precautions should be taken to avoid skin contact and inhalation, as is the case for almost all enzyme proteins.