Graduate Thesis Or Dissertation
 

Improvement of biological control agents : laboratory selection for fast larval development in the convergent lady beetle, Hippodamia convergens guerin-Méneville (Coleoptera: Coccinellidae)

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  • Hippodamia convergens Guerin-Meneville was selected for rapid development through five generations at four constant temperatures (18, 22, 26, and 30°C). Two levels of selection were used: intense and moderate. Differences in developmental rate, survivorship, live adult weight, aphid consumption, adult longevity, and fecundity were measured for both groups and an unselected line. The two selected lines exhibited significant differences in developmental rate after the first generation of selection. The differences increased by the fifth generation of selection. Average differences between selected lines at 18, 22, 26, and 30°C in development from egg to adult were 4.9, 3.0, 1.0, and 1.5 days, respectively. Individuals from the intense selected line had a lower developmental threshold (11.3°C) than the moderate selected line (12.0°C). Also, degree-day requirements from egg to adult were lower in the intense (266 DD°) than moderate (277 DD°) line. Wild type beetles accumulated 231 degree-days above a threshold of 13.6°C. Survivorship at cold temperatures significantly increased with selection for fast development. In addition, no significant differences occurred in either live adult weight, total larval consumption of prey, fecundity, or adult longevity. Larvae selected for fast growth consumed higher numbers of aphids per day and were more efficient metabolically in converting prey mass into body mass than slow growing larvae. Because of a lower developmental threshold and lower degree-day requirements, for complete development, beetles from the intense selected line may accumulate more degree-days throughout a year compared to a moderate selected line. Predictions of population growth, based on an equation for intrinsic growth rate, showed that beetles from the intense selected line would produce 1.6 and 1.4 times more individuals in a 60-day period than beetles from the moderate selected and unselected lines, respectively. The results suggest that intense selected beetles would develop faster earlier in the season and would produce higher population numbers under optimum conditions. Thus, selection of H. convergens produced superior beetles for future introductions in biological control.
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