Feeding behaviour and reproductive biology of Colorado potato beetle adults fed transgenic potatoes expressing the Bacillus thuringiensis Cry3B endotoxin

Colorado potato beetle (Leptinotarsa decemlineata Say) adult longevity and fecundity were studied on transgenic potato clones expressing a Cry3B endot oxin of Bacillus thuringiensis (Bt). Adult longevity and fitness were studi ed for the first 3 weeks after emergence. Beetle reproductive biology on hi ghly resistant clones, intermediary resistant clones and control potato pla nts was monitored by dissecting females after 7-15 days of feeding and also by analysing haemolymph protein content after 3 days of feeding. Feeding b ehaviour on transgenic plants expressing high toxin concentrations and on c ontrol plants was monitored individually for 36 newly emerged adult beetles feeding on leaf disks during the first two meals. Lethal Time(5)0 for adul t beetles feeding on transgenic clones as the sole source of food was not s ignificantly shorter than for beetles on control clones reared in a growth chamber. Differences tended to be larger when the experiment was conducted in a greenhouse with a less optimal temperature range (LT(5)0 = 9.52 and 10 .45 days for two transgenic clones and 13.86 for control). In contrast, fem ale egg production on transgenic plants was almost totally inhibited. Disse ction studies indicated that adult males living on high-level Bt-expressing transgenic potatoes were still able to mate and produce mobile sperm, but the females were impaired in their reproductive ability since their ovaries were generally not fully developed. An examination of the haemolymph revea led the protein concentration in females living on transgenic plants to be dramatically reduced (congruent to 50%), and electrophoresis showed a reduc ed content of vitellogenin in these samples. Feeding behaviour of adult Colorado potato beetles was not affected by the different food plants; this indicates that transgenic potato plants were re adily accepted as host plants by beetles. The effects of these findings on the use of transgenic plants as a means of L. decemlineata control are disc ussed.