Analysis of a Chemical Defense in Sawfly Larvae: Easy Bleeding Targets Predatory Wasps in Late Summer

Contact of certain sawfly larvae with predators frequently elicits an easy bleeding behavior involving local disruption of the integument and release of hemolymph droplets. The efficacy of this putative antipredator defense was investigated in the turnip sawfly, Athalia rosae, by using common garden experiments in which particular guilds of predators were excluded, and through manipulations of the chemical defense of larval prey. After 3 d of exposure to walking and/or flying arthropod predators, the proportion of surviving sawfly larvae remained quite high at 71.3% in midsummer, but dropped to 37.5% in late summer. However, Pieris rapae caterpillars without the bleeding defense were killed within hours by predatory wasps (Vespula vulgaris). Topical treatment of P. rapae caterpillars with sawfly hemolymph or sinalbin, a glucosinolate sequestered by the sawflies, revealed that the easy bleeding of A. rosae is an efficient defense against wasps, partially due to this compound. These experiments are the first to demonstrate the efficacy of this chemical defense mechanism in a natural setting.     

Glucosinolate Content and Susceptibility for Insect Attack of Three Populations of Sinapis alba

Sinapis alba is less susceptible to damage by insect pests than Brassica napus. We investigated the composition and distribution of glucosinolates in different plant parts in three populations of S. alba; two populations selected for low-seed-glucosinolate content and one commercial cultivar. We have assessed the susceptibility of low-seed-glucosinolate content populations of S. alba to four insect pests, a flea beetle, a pollen beetle, and two species of aphids. Over 90% of the total glucosinolates in the cotyledons of the three populations of S. alba consisted of sinalbin. There was no difference in feeding damage by flea beetles on different S. alba populations at the cotyledon stage, nor was there a difference in sinalbin concentration of cotyledons. Total glucosinolate levels were highest in younger plant tissues. Sinalbin declined as a proportion of total glucosinolate content in later growth stages, especially in the low breeding lines. Reproduction by aphids was the same on all three populations despite differences in sinalbin content of the S. alba leaves at the growth stage tested. The specialist aphid, Brevicoryne brassicae, was found mainly on young tissues, while the generalist aphid, Myzus persicae, was found predominantly on older plant parts. There was no difference in oviposition by pollen beetles between the S. alba populations, despite the fact that on one population total glucosinolate concentration and the proportion of sinalbin found in the buds were much lower than on the other two populations.     

Supercritical Fluid Chromatography of Myrosinase Reaction Products in Ground Yellow Mustard Seed Oil

ABSTRACT: Escherichia coli O157:H7 can survive the dry fermented sausage manufacturing process. Compounds generated by enzymatic hydrolysis of glucosinolates present in ground mustard have shown potential antibacterial properties against E. coli O157:H7. In the present study, supercritical fluid chromatography (SFC) was used to investigate degradation products of 4-hydroxybenzyl glucosinolate (sinalbin), the major glucosinolate present in yellow mustard seed. Using SFC the concentration of the reactive component, 4-hydroxybenzyl isothiocyanate (PHBITC) was measured during the hydrolysis of sinalbin with myrosinase while imposing the temperature and pH regimen used for the fermentation phase of dry fermented sausage production. The PHBITC concentration grew to a maximum after 7 h and decreased rapidly. The concentration of 4-hydroxybenzyl alcohol increased rapidly to reach a maximum at 31 h and stayed at that level. The concentration of 4-hydroxybenzyl cyanate increased up to 24 h, then decreased to 65% of its maximum, and stayed constant. The stability of 4-hydroxybenzyl isothiocyanate in the presence of maltodextrin in this system was investigated. It was concluded that the major PHBITC loss in the mixture of the oil with maltodextrin occurred within the first 4 d of its storage. Practical Application: During the work 4-hydroxybenzyl isothiocyanate (PHBITC) was measured during the hydrolysis of sinalbin with myrosinase while imposing the temperature and pH regimen used for the fermentation phase of dry fermented sausage production. The results on PHBITC stability in maltodextrin presented provide precautionary information on the limited ability of this material to afford stability of PHBITC expected.