Agriculture Reference
In-Depth Information
Insects
Insect pests are a major problem in agriculture, including tropical fruit
production. Most insects are harmful because they chew plant parts or
suck their fl uids. Some insects are borers that damage the branches or
stems. Additionally, some sucking insects can transmit viruses, viroids and
mycoplasmas that cause diseases if they come from an infected plant. There
are also benefi cial insects such as honey bees, silk worms, those involved in
pollination, predators that eat harmful insects and parasites that lay their eggs
into the insect pest; the parasite eggs hatch and the larvae consumes the pest
larvae or pupae.
Insect control using integrated pest management (IPM) requires
knowledge of the insect life cycle and habits. Questions asked include: Where
do they lay their eggs? How much time does it take to become larvae? How long
are the larvae active before becoming pupae? Where do they stay during these
stages? What are their feeding habits? What species and what part of the plant
do they attack? What are their migratory habits? Knowing this information
allows the IPM person to design a strategy for controlling them.
A major pest such as fruit fl ies requires a preventative approach for its
control, since once the fl ies lay their eggs, the fruits are dii cult to market
unless subject to a kill or sterilization treatment. Frequent preharvest sprays
and traps can be used for fruit fl y control, though costly. Fortunately, fruit fl ies
do not generally lay their eggs into unripe fruit, therefore harvesting at early-
ripening stages avoids major fruit fl y injury. Fruit fl ies are a signifi cant insect
problem in fruit export, since the USA, Japan and others have very stringent
quarantine regulations and in many cases require the fruit to be treated
before entry.
Insect traps in the fi eld (Fig. 4.6a) give an indication about the insect
species present and their population size, and this is used to decide if spraying
is necessary. Some traps used have light as an attractant and have either a
pan fi lled with soapy water to reduce surface tension so that the insect sinks
into the water, or kerosene or water with a contact insecticide is used to kill
them. Other traps use a lure, which can be a pheromone or a particular
scent that will make the insect go to the trap and be killed in similar ways.
Another way is the use of attractive plastic sheets with a sticky substance in
the nursery (Fig. 4.6b) and in the fi eld (Fig. 4.6c), which will immobilize and
thus kill the insect.
Among the exclusion methods used are barriers and tall plant fences,
which will not keep insects out but will reduce the number of insects visiting
the fi eld. Anti-insect fabrics exclude insects completely but they are expensive,
although they are used to exclude aphids from papaya trees in some areas (see
Fig. 3.9b). Another exclusion method is bagging the fruit (Fig. 4.6d), which is
very ef ective in preventing fruit fl y and other insects from laying eggs.
