Effects of Toxicants, Temperature, and Resistance on Metabolism and Gas Exchange Patterns of the Beet Armyworm, Spodoptera exigua (Hübner), and the German Cockroach, Blattella germanica (Linnaeus)
Type of DegreeDissertation
Entomology and Plant Pathology
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Components of the respiratory physiology and water relations of Bacillus thuringiensis Cry1C resistant and susceptible beet armyworms, Spodoptera exigua, and pyrethroid resistant and susceptible German cockroaches, Blattella germanica, were investigated. Standard metabolic rates of third and fifth instar larvae and 1 to 7 day old pupae of S. exigua and adult B. germanica were determined using closed-system respirometry. Standard metabolic rates (ml g-1h-1) of third instar resistant larvae reared continuously on toxin (CryonT) were significantly greater than resistant third instar larvae reared on toxin for 5 days and reared thereafter on untreated diet (Cry5dT), resistant larvae reared on untreated diet (CryReg), and the susceptible parental strain (SeA) reared on untreated diet. No difference in metabolic rates among treatment groups was detected for fifth instar larvae. CryonT larvae and pupae weighed significantly less than those receiving other treatments. One day-old pupae of all treatment groups exhibited a high metabolic rate. Metabolic rates of all treatment groups declined between days 2 and 4 then increased between days 4 and 7. Overall metabolic rate (ml g-1 h-1) was not significantly different between strains of B. germanica but different strains reacted differently to increasing temperature. Mean cockroach body mass differed significantly between strains and metablic rate (ml g-1 h-1) scaled with temperature and mass in all strains. Resistant and susceptible S. exigua pupae and adult B. germanica exhibited a discontinuous gas exchange cycle (DGC), which was characterized using flow-through respirometry at 10-35oC. DGC was exhibited mostly at 10oC; frequency of cyclic CO2 release increased with increasing temperatures. There was no clear distinction between the closed and flutter phases in most DGCs, from B. germanica. The three phases were distinct in S. exigua. Respiratory water loss was 4.5+1.3%, 2.1+2.4%, 3.4 + 1.9% and, 4.4 +2.2% for toxin exposed S. exigua, unexposed S. exigua, insecticide exposed B. germanica and unexposed B. germanica, respectively. Toxin exposed S. exigua pupae had a significantly greater cuticular permeability (26.01+1.9 µg cm-2 h-1 mmHg-1) than unexposed pupae (9.64+0.9 µg cm-2 h-1 mmHg-1). The cuticular permeability of B. germanica was 2.26 µg cm-2 h-1 mmHg-1 for the resistant strain and 3.42 µg cm-2 h-1 mmHg-1 for the susceptible strain. In both strains of S. exigua and B. germanica cuticular transpiration (>93%) far exceeds respiratory transpiration.