This is a nice cowpea field, but we see some
strange dots on the leaves. These dots are eggs
of the legume pod borer. Inside the egg,
there is a young caterpillar developing. The caterpillar hatches from the egg and wanders on the plant
looking for cowpea flowers to feed upon. The young caterpillar
bores a hole in the cowpea flower and starts to feed inside it. Flowers attacked by the caterpillar can be detected by the presence
of frass around the hole. The attacked flower will drop prematurely. After feeding on the flowers, the caterpillar moves to growing
cowpea pods and destroys their seeds. Once completing the five larval stages, during the eleventh to twelfth day, the caterpillar spins a silk thread
and drops to the ground, transforming itself into a pupa. After five to six days,
a moth emerges from the pupa; this is the adult stage of the legume pod borer. While the moths are flying around the field, the female moth
will encounter a male and mate. After mating, the gravid female
will find a suitable place to drop its eggs. In the meantime, the caterpillars are continuing
to destroy cowpea flowers and pods. But now, a tiny parasitic wasp
attacks the eggs of the pod borer. The wasp inserts its egg
into the egg of the pod borer with an ovipositor. On the right side, the egg is parasitized by the wasp
and turns black. Instead of the caterpillar, it is a new wasp,
which emerges from the parasitized egg. The egg has been killed so there is no more
caterpillar emerging from it and causing damage to the plant. On the left hand side is a field with no wasps. The caterpillars continue to grow
and eat cowpea flowers and pods. While the wasps are flying around the field, the female wasp
will encounter a male and mate. After mating, the gravid female will find a new egg
of the pod borer to insert its egg. By killing the egg of the pod borer, the parasitic wasp contributes to keep
the cowpea crop free of damages by this pest. The action of killing
the egg of the pest by the wasp is called biological control or biocontrol.