Today we will talk about the cabbage butterfly (Pieris brassicae), one of the main enemies of farmers and gardeners as it feeds in its larval stage on cabbages and other brassicas.
This insect, as almost all have three clearly differentiated phases, the larval phase, the pupal phase or metamorphosis and the adult phase, in this case a white butterfly with black front wing tips.
The main and only damage of this insect falls on the larval phase, which we know as caterpillars. Be careful not to confuse them with worms. These butterfly larvae can reach up to 50 mm in length, are yellow and white in colour, with various black spots. If you look closely, you can see their legs, 3 pairs of legs just behind their head and 5 pairs at the end of their body.
The adult, however, no longer feeds by chewing the plants, but by squeezing the flowers, which is even beneficial for our plants. The male is white with black forewing tips and a black dot on each side, while the female has two dots on each side of her forewings.
Adults appear in spring, laying on the underside of the leaves, which do not take long to hatch. Depending on the temperature, they hatch in 5-15 days. It is curious that these caterpillars when they are born behave in a gregarious way becoming more solitary as they increase in size until they reach the age to carry out their metamorphosis approximately 15-40 days.
This butterfly can in the same year have up to 3 or 6 generations if the year has been good. Generations follow one another until the arrival of cold weather, which corresponds to these days, when it will spend the winter in the form of a pupa.
Caterpillars are very voracious and can produce intense defoliation, as well as indirect damage as their droppings accumulate in the leaf buds.
To eliminate this pest there are several methods, including chemical control, treating with cypermethrin, deltamethrin or indoxacarb, when plants are less developed. Another method is biological control, using Bacillus thurungiensis which is effective during the early stages of the caterpillar or with Apanteles glomeratus, which is a caterpillar parasitoid.
As a cultural measure, it is advisable to eliminate all those weeds that are cruciferous (Diplotaxis, Sinapis, Raphanus, etc.) to prevent them from feeding on this plant and becoming a focus of infection and passing on to ours.