Development of an integrated pest management strategy for the control of potato tuber moth Phthorimaea, Operculella (Zeller) (Lepidoptera: Gelechudae) in storage

The biological study indicated 10 overlapping generations of PTM [potato tuber moth] for one year. Screening of genotypes under three population pressures (low, medium and high) and different storage periods (two and four months) showed a consistent positive correlation between the number of eyes on tuber and the number of holes, a measure of severity of damage and ultimately the level of varietal resistance or susceptibility. Sprouts of all the genotypes were almost equally infested after two and four months of storage, indicating that PTM is not able to discriminate among cultivars once the sprouts have grown. Both one and twenty tuber antibiosis tests revealed variations in developmental stages (egg, larva, pupa and adult) of the pest with different genotypes. Based on the aforementioned test four genotypes: Huayro, Revolucion, Moro-Bole and Cica were selected and categorized as susceptible, low, moderately, and highly resistant, respectively. Tuber hardness test, analyses of bio-chemical components of tubers and scanning electron microscopy (SEM) of the tuber periderm (skin) were done to identify possible causes of varietal resistance to PTM. SEM examination showed variations in cellular layers of periderm among different genotypes implying the importance of periderm for the penetration of the larvae and ultimate varietal defense against PTM. Different treatment combinations were added to different levels of resistance to determine their effects after two and four months of storing tuber. After four months of storage, decis-treated tubers were analyzed for residue levels using high pressure liquid chromatography (HPLC). The residue level was found lower than the Maximum Residence Limit (MRL) in three genotypes (Revolucion, Huayro and Cica) while in one genotypes (Moro-Bole) it was a little higher than the MRL. Finally, in an effort to isolate possible effects of talc as a carrier of GV [granulosis virus], a separate experiment was conducted and results indicated that talc alone acts as a physical barrier against PTM. The efficacy of GV preparation, therefore, was attributed to the combined effects of GV and talc, and not of GV alone