Genetic relationships between development of insecticide resistance and reduction of egg size as a negative effect on the fitness of the diamondback moth Plutella xylostella (Lepidoptera: Yponomeutidae)

Abstract

Reciprocal crosses between susceptible (SS) and resistant (RR) lines to fenvalerate were conducted to determine whether or not there are any genetic relationships between insecticide resistance and reduction in egg size, as well to whether or not they affect the offspring fitness of the diamondback moth, Plutella xylostella. The dose-mortality regression lines of the F 1 hybrid of susceptible females and resistant males (SR) and resistant females and susceptible males (RS) were roughly intermediate between those of parental lines, i.e., SS and RR. This result indicates that the mode of inheritance of fenvalerate resistance was neither complete dominance nor recessive, with no sex-linkage. The egg size of RR lines was significantly smaller than that of the SS lines. The RS and SR lines have an egg size close to that of their own matrilineage. We considered that the mode of inheritance of resistance and that of egg size were different from each other, although the selection experiment showed that there is a negatively correlated response between these parameters. The survival rate of the RR lines was significantly lower than that of the SS lines. However, the survival rate of the RS lines did not differ from that of the SR lines. Reproductive fitness is discussed with regard to different egg sizes among parental lines and reciprocal crosses.

Rapid recovery of susceptibility under harsh environmental conditions in fenvalerate-resistant strains of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae)

“…Miniaturization of eggs was repeatedly observed in DBM resistant populations in several studies (Fujiwara et al, 2002;Chen and Nakasuji, 2004;Chen et al, 2006) as in our study. The DBM individuals used in these studies fundamentally originated from an insecticide-susceptible population maintained at Sumitomo Chemical Co. Ltd., although the stock cultures were established at different times and insecticide selections were conducted independently among these studies.…”

“…Ϫ2 mm 3 ) in the tenth generation selected by a sub-lethal dose of fenvalerate (Chen et al, 2006). In our study, the respective egg sizes of resistant lines 1 and 2 decreased to ca.…”

“…Egg size is considered to be a maternal effect that influences the life history traits of insects. Our previous study (Chen et al, 2006), however, suggested that egg size might affect biotic performance, e.g. survivability of premature insects, but not strongly.…”

“…Our previous study (Chen and Nakasuji, 2004) showed that eggs were miniaturized by insecticide selection in DBMs. Furthermore, egg size was a maternal inheritable trait (Chen et al, 2006). Small eggs reportedly correlated with low viability of offspring under harsh environmental conditions such as low humidity and high temperature (Fujiwara et al, 2002).…”

“…4) because the egg sizes of both lines were closer to that of the original susceptible population and also reached a plateau in later generations. Although it remains unclear whether close genetic relationships exist between resistance and egg size (Chen et al, 2006), resistant individuals hatched from small eggs are eliminated quickly from resistant populations under harsh environmental conditions. Therefore, susceptibility to insecticides recovered more quickly in Harsh lines than in Optimal lines in early generations free from insecticide pressure.…”