Effect of Different Potato Cultivars on Biological and Morphological Characteristics of Colorado Potato Beetle, Leptinotarsa decemlineata (Say) (Col.: Chrysomelidae)

Potato, (Solanum tuberosum L.) is an important crop with 5.24 million tons of production on 143000 ha of irrigated land in Iran. Numerous pests attack the Potato crop, among them the Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most important pest. This is a cosmopolitan pest and the most dangerous pest of Potato and other solanaceous crops in many areas of the world that can cause yield reduction of 30 to 50%. Due to interference of generations, usually all four biological stages of the pest (eggs, larvae, pupae and adult insects) are observed on the farm at the same time, so it is very difficult to control. The use of resistant cultivars is one of the important methods in integrated management (IPM) programs of this pest. Effective combination of pest control methods requires that information on pest growth and development be available on different Potato cultivars. Much research has been done on the biology and ecology of this pest, but there is not much research on the effect of cultivar on its biology and morphological characteristics, so in the present study, the biological and morphological indices of potato beetle, were studied on four Potato cultivars (Agria, Stima, Bridjet and Delikat).

First, the pest egg masses were collected from infected fields in west Azarbaijan province, Iran. Then, hatched larvae were reared for three generations on the studied cultivars under protected field conditions. Biology of the pest was studied in a greenhouse at 22±4°C, 65±5% Rh and natural light at 2018. After the emergence of the plants, one sleeve cage was set on each pot and 25 neonate larvae were released and reared. Incubation period and developmental time of larvae and pupae and mortalities of these stages were determined as antibiosis indices of the cultivars. Insects reared in greenhouses were used to study and measure the morphological characteristics of the pest. Head capsule width of different instars larvae, length and width of the male and female adults, weight of different instars larvae, the number of egg/egg mass and weight of adults (male and female) as morphological indices was measured. Data was analyzed with spss 21 statistical software in randomized complete block design and comparison of means was performed with Tukey’s HSD procedure in 5% level.

Cultivar had significant effect on many biological parameters (P<0.05). Significant differences were observed for all morphological indices (P<0.05). The longest developmental periods of larvae, pupae and total (larvae and pupae) were observed on Delikat cultivar with means values of 15.07, 12.90 and 27.97 days, respectively. The highest mortality of immature stages (larvae and pupae) was observed on Bridjet cultivar with average of 57.78%. The lowest head capsule diameter of the first, second and third instar larvae were observed on Bridjet, Delikat and Bridjet cultivars with means of 0.59, 1.01 and 1.55 mm, respectively. The lowest length and width of female adults were observed on Delikat with average of 10.60 and 6.44 mm, respectively and the lowest length and width of male adults were observed on Bridjet and Delikat with average of 10.04 and 6.07 mm, respectively. The lowest weight of first to fourth instar larvae were observed on Bridjet, Bridjet, Delikat and Delikat with means of 0.99, 4.17, 23.20 and 85.67 mg, respectively and lowest weight of male and female adults were observed on Delikat with average of 159.33 and 135 mg, respectively.

The results of the study showed that the cultivar not only affects all the biological characteristics of the Colorado potato beetle, such as the length of its development and survival rate, but also all the morphological characteristics of the pest, such as body size of different larval and adult’s insect. It also affected their size and weight of the pest. Based on the results of this study, Delikat and Bridjet cultivars were less favorable for Colorado potato beetle compared to Agria and Stima cultivars, which can be used in plant breeding programs to produce resistant cultivars.