Assimilated food, conversion

Many of the deleterious metabolic or chronic effects of plant allelochemlcals may be due to these Interactions. Many of the types of Interactions discussed In vertebrate nutrition literature may also be Important in insect dietetics (14). Certain allelochemlcals structurally resemble essential nutrients closely enough to compete metabolically (35, 36, 37, 38, 39, 40). Allelochemlcals may block the bloavallablllty of nutrients by reducing assimilation, efficiency of conversion of assimilated food, or the efficiency of conversion of ingested food (, 44, 46). 

Since insect fecal pellets contain both undigested food and nitrogenous waste products, Bhattacharya and Waldbauer (58) subtracted the urine content of the feces from the total weight of the fecal pellet. This provided better estimates of assimilation and conversion of assimilated food. Schmidt and Reese (57) noted that BCW larvae will feed upon their fecal pellets if no other food is available. Growth on fecal pellets is nearly as rapid as growth on diet, suggesting that much of the nutrient content of the diet is not assimilated. The result of fecal feeding on nutritional parameters is an overestimation of the AD and ECI and an underestimation of the ECD. 

The final section of Table 1 illustrates experiments in which 0.5 g of KOH or NaOH were added to 150 g of stock diet to make it more alkaline. Both diets had mildly deleterious effects on the larvae, but growth reduction occurred for different reasons. On the diet containing KOH, reduced DWG was a result of diminished food conversion, whereas the NaOH diet primarily reduced assimilation. As expected the Insect s overall ability to utilize the alkaline diet (ECI) decreased. 

Three of the most useful nutritional indices are assimilation (AD), efficiency of conversion of assimilated food (ECD), and efficiency of conversion of Ingested food (ECI). These and a number of other indices were recently discussed by Scriber and Slansky (22). If growth is inhibited, then it must either be reflected in the amount eaten or in one or more of these Indices or both. 

In recent western literature, Kt is interpreted as gross conversion efficiency and the western analogue of K2 is net conversion efficiency (Brett and Groves, 1979), but the biological sense of the two coefficients can be obscured by such generalized semantics. A better concept is efficiency of food consumption and assimilation for constructive processes (Zaika, 1983). 

The chemical half-life of DMSP in seawater is >8 years (Dacey and Blough 1987), which results in high abiotic stability under natural conditions (moderate temperatures and pH). Therefore, most of the DMSP removal is through enzymatic processes. In the microbial food web, dissolved DMSP has many fates and several recent reviews on the microbial pathways and involved mechanisms have been published (Bentley and Chasteen 2004 Kiene et al. 2000 Lomans et al. 2002 Yoch 2002). They all show that DMSP can be readily used in a complex network of enzymatic conversions. This versatility indicates that this single compound is of major importance for the nutrition of the bacterial community. Indeed, several studies have shown that DMSP alone can contribute 1 to 15% of the total bacterial carbon demand in surface waters. Moreover, DMSP assimilation can satisfy most, if not all the, sulphur demand of marine bacteria (Kiene and Linn 2000 Simo et al. 2002 Zubkov et al. 2001). Since the focal point of this section is the quantification of DMSP removal, only the overall effects of the main pathways originating from DMSP (Fig. 1) will be discussed here. 

The use of the term assimilation may be confusing to the reader. Rigler, in Edmondson and Winberg (1971), stated that it is used by physiologists ".. . to mean the conversion of digested food into the structural materials of the animal. ... 

Animals step up the protein content and quality of foods. Grains, such as corn, are much lower in protein content in cereal form than after conversion into meat, milk, or eggs. On a dry basis, the protein contents of selected products are corn, 10.45% beef (Choice grade, total edible, trimmed to retail level, raw), 30.7% milk, 26.4% and eggs, 47.0%. Also, animals increase the quality (e.g., biological value) of the protein—a higher proportion of the protein is assimilated by the body. 

Because many factors affect the assimilation of carotenoids from foods (Figure 2), conversion factors need to be considered. This is especially important when most sources of vitamin A are from provitamin A carotenoids in the population. Bioavailability of preformed vitamin A, i.e., retinol and retinyl esters, is not a major concern because 80-95% of them are absorbed. However, foods that are high in preformed retinol (liver, eggs, and fortified milk) are not necessarily consumed by everybody. When discussing carotenoids from food, four terms need to be defined (see Table 1) ... 

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