By DORIS KINYUA
Lepidopteran pests are chewing insect pests that cause damage mainly to leaves and petals making the flowers less Aesthetic and reduce their value. Caterpillars are the larval feeding and the most damaging/destructive stage of butterflies and moths from the insect order Lepidoptera. Caterpillars are seasonal pests to the flowers but when in season they result in major losses to the flower industry as one caterpillar can cause damage to more than one flower. In flowers there are different kinds of caterpillar species which include Helicoverpa armigera (Boll worms) and Spodoptera exigua and thus it’s important to know the exact pest that one has in their crop and out of these two, the helicoverpa species is the notorious and listed as a notifiable pest in the European market.
Helicoverpa armigera commonly known as African bollworm is the main caterpillar that infests flowers in green houses and outdoor ones. The are a pest of roses, carnations, hypericum, gypsophilla amongst other flowers. It is unique in that the moth lays its eggs singly on the roses and specifically on the softest parts of the crop. In roses the eggs are found on the flower buds and petals.
Temperature is the main force behind the speed of a life cycle.
The hotter it is the faster the lifecycle. The eggs are small, yellowish-white,
ribbed and rather dome shaped. The egg period is two days after which it
hatches to a larva- the caterpillar.
The caterpillar eats the eggshell to emerge after which it bolls making circular holes through the petals only to feed from inside the flower. There are 6 instars or stages of the caterpillar in a larval period of 16 days and the damage to the crop increases with increase in size of the caterpillar. These caterpillars are cannibalistic. As the larvae size increases ,its becomes difficult to control .
When a caterpillar matures it drops into the soil or the growth media to pupate. The pupa is shiny brown; about 16mm long with smooth surface and with two short parallel spines at the posterior tip of the body and the pupal period is 10 days at normal temperatures. The pupa is dormant and doesn’t feed.
When it rains the pupa emerges into an adult called moth with the male moths being greenish in color and females being brownish..The moths are nocturnal and thus not easily seen unless one has a trapping system like pheromone traps specifically for the helicoverpa or light traps or water traps.one female moth can lay around 3000 eggs in a lifespan of 10 days and thus one moth can cause an economically reputable damage to one greenhouse. These moths lay eggs closely soon after the rains start and thus its important to have an alert scouting system.
To successfully control this pest, an holistic approach is recommended and below points are Key.
- Scout the field thoroughly.
- Hit when the Caterpillar/Larvae size is small.
- Alternate modes of action of the chemical control options.
- Adapt an IPM approach in management of the pest.
Integrated control methods for this pest are as follows.
- Cultural Control-Use of pheromone Traps, Planting trap crops, use of Repellant sprays(Plant extracts).
- Biological Control-Use of Bacillus Thuringiensis strain Kurstaki and Aizawai
- Chemical Control-Use of Spinosyns (Delegate and Tracer),Methoxyfenozide(Runner)-IGR ,Indoxacarb etc.