The effect of vermicompost and humic acid on some of the interactions of the diamondback moth, Plutella xylostella (Lep.: Plutellidae) and host plants under laboratory conditions

Jafary-Jahed, Mahdieh (2019) The effect of vermicompost and humic acid on some of the interactions of the diamondback moth, Plutella xylostella (Lep.: Plutellidae) and host plants under laboratory conditions. Doctoral thesis, University of Mohaghegh Ardabili.

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Abstract

The diamondback moth, Plutella xylostella (L.) (Lep.: Plutellidae), is a key pest of cruciferous vegetables, throughout the world including Iran. The present study is including two groups of experiments. In first experiment, the effects of vermicompost and humic acid fertilizers on the population growth of P. xylostella and the root system development on six brassicaceous host plants including canola, broccoli, cauliflower, kohlrabi, red cabbage and white cabbage were investigated under the same experimental conditions. The results showed that brassicaceous plants fertilized by these fertilizers significantly reduced the immature survival rate of P. xylostella. Reared adults from larvae on the treated plants also showed statistically significant reductions in the longevity, oviposition period, and fecundity compared with the control. On canola, broccoli, cauliflower, kohlrabi, red cabbage and white cabbage, the values of R0 and r fertilized with both humic acid and vermicompost were significantly lower than control plants. We also found that on the plants fertilized with humic acid and vermicompost, the number of eggs laid was lower than control plants. The tested fertilizers improved the development of root systems and subsequently enhanced the plant tolerance to P. xylostella. Our results show that humic acid and vermicompost root application induces defenses in tested plants that have negative effects on the performance of P. xylostella. These findings will help to develop our knowledge regarding the effects of humic acid and vermicompost fertilizers on the resistance of plants to P. xylostella. In second experiment, the oviposition preferences and larval development of P. xylostella were evaluated in the laboratory on the host plants. The results showed that female and male adults from larvae fed on cauliflower and canola lived longer than those fed other plants. Also, the oviposition period was longest for females reared on cauliflower (5.54 days) and shortest on kohlrabi (2.68 days). Significantly more eggs were oviposited on cauliflower (163.71 eggs per female) than on the other plants. The differences in total development times of immature stages on Brassica plants tested were significant, being shortest on cauliflower (17.60 days) and longest on kohlrabi (21.12 days). The moths reared on cauliflower had significantly higher R0 and r values (65.46 offspring per individual and 0.200 day-1, respectively). The lowest R0 and r values were obtained when individuals fed upon Kohlrabi (12.71 offspring per individual and 0.105 day-1, respectively). In free-choice situation, oviposition on canola and cauliflower were similar, but numbers of eggs deposited on these plants exceeded other plants. The amounts of glucosinolate were significantly greater in canola and cauliflower and the lowest in red cabbage. Correspondingly, diamondback moth longevity, duration of the oviposition period and number of eggs produced per female, all were lower when the larvae fed on kohlrabi. Our finding showed that kohlrabi was the non- preferred host plant for feeding of P. xylostella.

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