The white-spotted chafer,
Diet and growth conditions have been previously investigated (Kwon, 2009). In this study, we sought to characterize the effect of supplementing insect feed with adsorbents such as clay and charcoal because they have been shown to remove contaminants such as heavy metals and bio-waste (Babel and Kurniawan, 2003). To improve the quality of the larvae, these two additives were added to standard commercial diet used for
Second instar larvae of
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Feeds with Different Additives
Second instar larvae were fed fermented oak sawdust diet purchased from a commercial supplier in Hoengseong-gun, Gangwon-do, Republic of Korea. To test the effects of feed additives, charcoal and/or clay were added at the indicated concentrations (Table 1). These additives were suspended in an equal weight of tap water and then mixed with the basic feed as described in Table 1.
[Table 1.] Seven treatments for feed composition with two additives, charcoal and clay.
Seven treatments for feed composition with two additives, charcoal and clay.
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Rearing Condition and Experimental Design
Second instars were reared in round petri dishes (98 mm diameter x 15 mm depth) with sufficient amount of the designated feed at 25 °C with ca. 40 % humidity and a 12:12 h (L:D) photoperiod. We measured the body weight of each larva, and provided feed once per wk. Ten larvae were randomly selected for each feed treatment and maintained for approximately 17 wk until most second instars had pupated. Seven different treatments of different additive combinations (10 larvae each) were replicated three times. Larvae were weighed once per wk for 17 wk and development stage of each individual was checked until emerging adults. Larval weight, weight gain per wk, cumulative gain, weight prior to pupation, and time of pupation were calculated. The significance of each treatment was determined and compared to the control treatment using a
Larval body weights generally increased 0.105 ± 0.004 g (mean ± S.D.) per wk over the 17-wk experiment (Table 2). However, larvae gained less weight during the latter part of the larval period (Fig. 1). Three treatments – clay 25, charcoal 25 + clay 25, and clay 50 – showed no significant differences compared to the control feed containing no adsorbent (Fig. 2). The maximum weight increase was observed at wk 3 for two treatments (control and charcoal 50 + clay 50) and at wk 4 for five treatments (charcoal 25, clay 25, charcoal 25 + clay 25, charcoal 50, and clay 50) (Table 2). After that time point, weight gain gradually decreased. Moreover, weight decreases were also observed after wk 10, which may be attributed to the secretion of special proteins to form the pupal cell as a defense mechanism against unfavorable environmental factors in preparation of pupation (Lee
Mean and standard deviation of larval weight increases based on seven different feeds compositions with two feed additives, charcoal and clay
Larval body weight prior to pupation was also analyzed (Fig. 3), because it is an important correlate of pupation rate and ultimate size of the adult beetle and therefore, the weight and size of prepupal larvae can be used as an indicator of adult insect quality (Sehnal, 1985: Leather, 1988). Although not significant, four of the treatments resulted in lower pupal weights compared to the control treatment. The treatments with clay 25 and clay 50 were similar to the control treatment (Fig. 3). In addition, the time for pupation was also compared for seven treatments (Fig. 4), larvae reared on charcoal 50 required the longest time for pupation (17.7 wk) whereas those reared on clay 25 required the least time for pupation (16.0 wk).
Among six different feeding regimens, clay 25 was determined to be the best for rearing