Virapong Noppun

Cuticular penetration of S-fenvalerate in fenvalerate-resistant and susceptible strains of the diamondback moth, Plutella xylostella (L.)

Abstract The cuticular penetration of fenvalerate was investigated in two fenvalerate-resistant (OKR 84 -FR and KAR 84 -FR) and two susceptible (OKR 84 and KAR 84 ) strains of the diamondback moth, Plutella xylostella (L.). Cuticular penetration of S -[ 14 C]fenvalerate into larvae of the resistant stains was slower than that of the susceptible strains. The resistant strains showed lower amounts of internal accumulation of S -[ 14 C]fenvalerate. However, the susceptible strains seemed to show higher rates of S -[ 14 C]fenvalerate excretion than the resistant strains. Reduced cuticular penetration of S -[ 14 C]fenvalerate was considered to be an important mechanism of fenvalerate resistance in the diamondback moth.

Heritability estimates of phenthoate resistance in the diamond-back moth

Realized heritabilities were estimated for the character of phenthoate resistance in two local strains of the diamond‐back moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae), by performing artificial laboratory selection for resistance and susceptibility to phenthoate. Heritability estimates indicated that such traits are moderately heritable (ĥ2 = 0.42 and 0.41 in the resistant selection and ĥ2 = 0.31 and 0.21 in the susceptible selection), and give an experimental basis accounting for rapid evolutionary changes of phenthoate resistance observed in field populations of this insect.

Laboratory selection for resistance with phenthoate and fenvalerate in the diamond-back moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae)

Abstract Diamond-back moth was tested for resistance to phenthoate and fenvalerate. The Okinawa (OKR) strain had decreased in insecticide resistance to all insecticides tested, except methomyl, and this species and the Osaka susceptible (OSS) strain of the diamond-back moth were selected for resistance to phenthoate utilizing the spraying method. High levels of resistance to phenthoate could be obtained after eight selections during nine generations. At LD 50 and LD 95 levels, the OKR-selected (OKR-R) strain exhibited 172- and 287-fold resistance to phenthoate, while the OSS-selected (OSS-R) strain exhibited 194- and 289-fold resistance, respectively. No significant difference in the rate of development of phenthoate resistance between the OKR-R and OSS-R strains was observed. On the other hand, selection for resistance with fenvalerate in the OKR strain was limited: only slight resistance could be obtained after 16 selection treatments for 23 generations.