Effects of mixed cropping on population densities and parasitism rates of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Abstract

Effects of mixed cropping and barrier crops on the population density and parasitism of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated in field plots of cabbage grown in Bali, Indonesia. The densities of P. xylostella at larval and pupal stages, as well as the overall density at larval plus pupal stages, were significantly lower in cabbage/coriander mixed cropping subplots than in cabbage monoculture subplots. Parasitism of P. xylostella by the larval parasitoid Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was not significantly different between the mixed and monocultural cropping systems. These results do not support the so-called enemies hypothesis, but suggest that disruption of the host searching behavior of female moths by neighboring non-host plants is the mechanism behind the associational resistance observed in the coriander mixed cropping system. The inclusion of a Napier grass barrier between mixed crop and monoculture subplots did not affect the influence of mixed cropping on larval and pupal densities. Therefore, Napier grass, which is used locally as a fence for preventing livestock invasion of fields, would not obstruct the pest-reducing effect of coriander/cabbage mixed cropping.

Cover Crop Mulch and Weed Management Influence Arthropod Communities in Strip-Tilled Cabbage

“…The enemies hypothesis (Elton 1958) suggests that increased habitat complexity will increase attack rates of herbivores by natural enemies; however, in other studies in cabbage, reduced predation and parasitism have been observed in intercropped plots and higher biocontrol in monocultures (Bjorkman et al 2010, Adati et al 2011. Complex habitats with noncrop plants such as weeds can host a greater diversity of herbivores, supporting a greater diversity of natural enemies within an agricultural Þeld (Andow 1988).…”

Screening barrier plants to reduce crop attack by sweet potato weevil (Cylas formicarius)

“…Barrier plants have been used around crops to reduce the number of viruliferous insects reaching the focal crop in a plant pathology context, but this technique can also be used to intercept other types of pests . Successful non‐disease management use of barrier plants include Napier grass ( Pennisetum purpureum Schumach) around maize against lepidopteran pests and coriander around cabbage against diamondback moth ( Plutella xylostella L.) . Barrier plant use is – in logistical terms – similar to trap cropping.…”

Introduction: host plant choice and feeding ecology of insects

“…Plant phenotypic traits that modulate insect–plant interactions, as shown in many examples above, could be induced following herbivory. However, such traits could also be inducible due to cultural manipulations in agricultural landscapes (Adati et al., ; Mahdavi‐Arab et al., ). Lund et al.…”

“…Phenotypic changes in host plants that are perceived by herbivores are often a result of differential regulation of induced defenses following herbivory (Walling, 2000;de Sassi et al, 2012). Sometimes, phenotypic changes in host plants could be induced by agronomic practices, and they are also perceived by herbivores (Adati et al, 2011;Mahdavi-Arab et al, 2018). The goal of scientists engaged in insect-plant interactions has been two-pronged.…”

“…Plant phenotypic traits that modulate insect-plant interactions, as shown in many examples above, could be induced following herbivory. However, such traits could also be inducible due to cultural manipulations in agricultural landscapes (Adati et al, 2011;Mahdavi-Arab et al, 2018). Lund et al (2019) describe the relevance of habitat structure, plant nitrogen level, and predator presence as short-and long-distance cues that could influence oviposition of the butterfly Pieris rapae L. (Lepidoptera: Pieridae).…”