Three questions regarding possible benefits of mixed diets for the specialist aphid predator, Coccinella septempunctata larvae were investigated. (1) Do aphids species from different host plants complement each other nutritionally? (2) Is a mixed diet of high‐quality aphids beneficial? (3) How does the quality of mixed diets depend on the quality of constituent species? All mix‐combinations of aphid species of high (Metopolophium dirhodum), intermediate (Myzus persicae), and poor food quality (Aphis sambuci), and the three single‐species diets were compared. A mixed diet of two high‐quality species (Sitobion avenae and M. dirhodum) was also compared with single‐species diets. Larvae that were given pure A. sambuci and a mixed diet of A. sambuci + M. persicae died within 18 days and none of the larvae developed to fourth instar. Metopolophium dirhodum was generally of higher quality as food than M. persicae, whereas the mixed diet of M. dirhodum + M. persicae was intermediate. Sitobion avenae and M. dirhodum were found to have approximately the same food value. Coccinella septempunctatam larvae that were offered a mixed diet of these two high‐quality aphids gained no extra advantage. Overall, no benefit from mixing of aphid species was found. The quality of mixed diets depended on the quality of the constituent species.
Asperphenamate is a small peptide natural product that has gained much interest due to its antitumor activity. In the recent years numerous bioactive synthetic asperphenamate analogs have been reported, whereas only a handful of natural analogs either of microbial or plant origin has been discovered. Herein we describe a UHPLC-HRMS/MS and amino acid supplement approach for discovery and design of novel asperphenamate analogs. Chemical analysis of Penicillium astrolabium, a prolific producer of asperphenamate, revealed three previously described and two novel asperphenamate analogs produced in significant amounts, suggesting a potential for biosynthesis of further asperphenamate analogs by varying the amino acid availability. Subsequent growth on proteogenic and non-proteogenic amino acid enriched media, revealed a series of novel asperphenamate analogs, including single or double amino acid exchange, as well as benzoic acid exchange for nicotinic acid, with the latter observed from a natural source for the first time. In total, 22 new asperphenamate analogs were characterized by HRMS/MS, with one additionally confirmed by isolation and NMR structure elucidation. This study indicates an extraordinary nonribosomal peptide synthetase (NRPS) flexibility based on substrate availability, and therefore the potential for manipulating and designing novel peptide natural products in filamentous fungi.
Larvae of Coccinella septempunctata were reared on three aphid diets, consisting of pure Rhopalosiphum padi, pure Metopolophium dirhodum, and an equal mix of these aphid species. In the pupal stage, the activities of three detoxifying enzyme systems — glutathione S-transferase (GST) with 1-chloro-2,4-dinitrobenzene as substrate, glutathione peroxidase with hydrogen peroxide as substrate (GSH-Px[H2O2]), and glutathione peroxidase with tert-butyl hydroperoxide as substrate (GSH-Px[TBH]) — were assayed. Growth rate, measured as the total protein content of the pupae, was significantly higher in the mixed-diet group than in the R. padi group, whereas that of the M. dirhodum group was intermediate. GST showed lower activity in larvae on a pure R. padi diet and a mixed aphid diet than on a pure M. dirhodum diet, whereas the variation in GSH-Px[TBH] was independent of diet. GSH-Px(H2O2) showed a significantly higher activity in the R. padi group than in the M. dirhodum group, whereas that of the mixed-diet group was intermediate. Thus, feeding on the low-quality aphid, R. padi, inhibited GST and activated GSH-Px(H2O2). The induction of GSH-Px[H2O2] indicated elevated oxidative stress. This may have been caused by toxic compounds in the R. padi.
Some ladybeetles are specialist predators of aphids, coccids or other prey, although they often eat a variety of species from their focal prey taxon. In addition, the diet is often supplemented with alternative prey. How larvae of the aphidophagous Coccinella septempunctata L. utilize a non-aphid alternative prey (fruit-fly larvae Drosophila melonogaster Meigen) is compared with adequate (i.e. high-quality) aphid prey provided alone (monotypic diet) or in mixed diets. The alternative prey are presented either nutrient-enriched (i.e. raised on dog food supplemented medium) or not (raised on pure medium). Ladybird performance (survival, growth and development) is poor on the pure fly larvae diets, and also reduced when given mixed diets compared with the pure aphid diet. Nutrient enrichment of the fly larvae has no positive effects. The physiological background for the differences in food value, as indicated by performance in life-history parameters, is a strong pre-ingestive effect (i.e. reduced consumption of fly larvae compared with aphids) and a post-ingestive effect (i.e. reduced utilization of assimilated larval fly tissue), whereas the assimilation efficiency of the consumed fly larvae is as high as that of aphids. The results show a physiological trade-off resulting from prey specialization that reduces the possibility of utilizing alternative prey when the availability of aphids is scarce. Connected with this is a high robustness against variation in prey nutrient diversity and composition; the ladybird shows little positive response to dietary mixing (i.e. neither mixing of adequate aphids, nor of aphids and alternative prey) or to nutrient enrichment of prey. This contrasts with the results from generalist predators (spiders), where similar treatments lead to strong effects on life-history parameters.
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