Diamondback moth larvae cause a serious economic damage to many cruciferous plants including broccoli, Brussels sprouts, cabbage, cauliflower, collard green, kale, kohlrabi, mustard, radish, turnip etc. After hatching from eggs, first stage larvae generally mine into leaf tissues. While feeding internally, first stage larvae molt into second stage larvae that move out of the mines. These larvae then start feeding externally on the underside of the leaves. Typically they scrap lower surface of leaf and leave its upper surface intact giving see-through window effect. Scraped tissues then dry, crack and create holes on the leaves. In case of severe infestation, diamondback moth larvae can completely skeletonize leaves that can lead towards the severe losses of crop yields.
Adults: As name implies, adult moths have distinctive diamond shaped pattern on their back.
Eggs: Eggs are about 0.5 mm in length, flat, oval, pale yellowish and laid singly or in small clusters on the leaves.
Larva: Diamondback moth larvae develop through four stages/ instars. Larvae are easily recognized due to their typical body shape, which is tapered at both head and tail ends. The presence of a pair of pro-legs at the tail end of the larva gives them a distinguishing “V” shape. First stage larvae are light yellow whereas matured larvae are green in color. Mature larvae are about 10-12mm in length with distinctive white marks on their body. When disturbed, these larvae wriggle quickly, move backwards and get away by spinning down on a silken thread.
Pupae: Mature larvae pupate in silken cocoons on the underside of the leaves. Pupae are greenish in color at the beginning but they turn brown before emergence of adults.
Diamondback moths generally take 30-40 days to complete their life cycle, depending on weather conditions. Adults are short lived and generally active during nights. After mating, females lay eggs singly or in small masses along the veins on both sides of the leaves. Eggs hatch within 6-7 days into tiny larvae that develop through 4 developing stages (instars). Matured larvae then pupate in silken cocoons on the underside of the leaves. Adults of diamondback moth generally emerge from pupae within 6-10 days. Depending on the climate, diamondback moth can complete about 5-10 generations within a year.
Natural enemies like egg parasitic wasps and predatory insects can be used as biological control agents for the control of diamondback moths.
Egg Parasitic wasps generally parasitize eggs of diamondback moths by depositing their own eggs inside the eggs of diamondback moths. Then eggs of wasps hatch into small larvae that immediately start feeding on the embryos of diamondback moths and preventing the further development of larva.
Adults of both Assassin and spined soldier bugs use their piercing and sucking type of mouthparts also called beaks for killing and feeding on the body content of the larvae of diamondback moths. However, predatory spined soldier bugs first use their beaks to inject a paralyzing toxic substance into the larvae and then for feeding on the body content of the larvae of diamondback moths.
Following parasitic wasps and predatory insects can control Diamondback moth organically