Diamondback moths going after an unusual crop in British Columbia
Last week, I visited a commercial greenhouse in Abbotsford and discovered diamondback moth infestation on pepper plants. This is the first evidence of diamondback moth feeding on peppers.
Diamondback moth is known to feed exclusively on crucifers such as canola, mustard, horseradish, cabbage, broccoli, Brussels sprouts, and other cole crops—a group of plants that contain glucosinolates for their defense against insects and diseases. Diamondback moth, over time, has adapted to glucosinolates and started using some of these chemicals as cues for host location, egg laying, and feeding activities.
Diamondback moth is among the “leaders” of the most difficult insect pests and costs over $4 billion in annual control on crucifers worldwide. It was the first crop insect to develop resistance to DDT and is now resistant to almost every insecticide applied in the field, including Bt (Bacillus thuringiensis). It has four life stages: egg, caterpillar, pupa, and adult. Caterpillars destroy crops by eating leaves, flower buds, flowers, and fruit. Total crop loss may occur, as sometimes growers are forced to plough down their standing crops despite multiple insecticide applications.
Diamondback moth is going after peppers, although pepper plants do not contain glucosinolates, but have different chemicals such as capsaicin. Initially, I thought the insects on peppers were due to spillover from the nearby crucifers, but there were no such plants in the vicinity.
Reports exist that diamondback moth is able to switch to non-host plants in the absence of natural crucifer hosts. For instance, it shifted from cabbage to adjacent field peas in Kenya in 1999. Peas are considered “neutral hosts” as they do not seemingly contain anti-herbivore chemicals. In 2004, this insect really liked lettuce in a Japanese lab. Recently, together with my colleagues in Alberta, I reared it successfully on two non-host but close relatives of crucifers: cleome and garden nasturtium. (See our paper in Canadian Entomologist.)
I am interested in evaluating the biology, ecology, and management of diamondback moth on peppers, and ecological consequences of the recent host shift. This host switch could potentially influence the way people control pests on their crops. Growers, hobby gardeners, and pest control specialists need to monitor this pest not only on cruciferous crops but peppers as well.