Rice Production: Chapter 10 - Insect pests of rice

Introduction

In Sierra Leone, as in most regions in the developing world where irrigated rice is grown, insect pests can be a major problem. Tropical conditions favor the year-round proliferation of insects, and double-cropping practices provide a steady habitat for feeding and breeding. In order -to take preventative measures against insect pests, the farmer must be able to recognize crop damage and identify which insect pest is responsible. This chapter provides a brief introduction to the major insect pests of rice in Sierra Leone, grouped according to the type of crop damage they inflict.

I. Stem Borers

Rice stem borer

a) Crop Damage

Rice stem borers are one of the most destructive types of insect pests of rice, occurring regularly and afflicting plants from seedling to maturity. Stem borers are the larval stage of any one of several species of winged insects which lay their eggs on the leaves or stems of the rice plant. When the egg hatches, the larva emerges, bores into the inside of the culm, and feeds on the interior of the stem. While feeding, the borer cuts off the growing part of the plant from the base, causing the tiller to die. Farmers generally cannot see the borer unless they cut the stem open. The presence of stem borers is most often determined by signs of crop damage

To determine the presence of stem borers, look for the following signs:

- dead hearts (young tillers which have dried up and died after borers have cut off the growing part from inside)

- white heads (empty, whitish panicles resulting from stem borer attack after panicle initiation had already occurred)

- holes in the stems (indicate where the borer entered the stem)

- presence of adult insects b) Species Most Common in Sierra Leone

Name	Larva	Adult
Striped stem borer	light brown larva with 5 thin stripes length to 17 mm	dirty brown moth(dark spots on wings)
Pink stem borer	pink larva with a dark head; segmented length to 25 mm	dark brown moth(white band across wings)
White stem sorer	creamy white larva length to 17 mm	white moth
Yellow stem borer	yellowish larva length to 17 mm	straw-colored moth(pointed head)
Diopsis or Stalk-eyed fly	white larva with sets of "feet" length to 25 mm	rust-colored bug with eyes at the end of stalks

II. Leaf Cutters/Leaf Feeders

a) Crop Damage

Leaf cutters and leaf feeders include a wide variety of different species of insects Although they can attack at any point in the crop cycle, damage is generally most heavy the seedling and tillering stages, when the leaf tissues are tender and succulent.

To determine the presence of leaf cutters/leaf feeders, lock for the following signs:

- irregular holes eaten into the leaf surface

- skeletonizing of leaf blades (i.e. leaves eaten down to the midribs)

- cut-off-leaf tips

- pieces of leaves floating in the water (also cases - see note on caseworm below)

- presence of insects (many species of leaf cutters/leaf feeders are easily observed, e.g. caterpillars grasshoppers)

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Caterpillars	various sizes and markings	butterflies and moths
Crasshoppers	various sizes and markings
Army worms	black worms length, to 35 mm (appear periodically in mass concentrations)	hair:, brick-red moth
Caseworm*	pale green larva length to 25 mm	dirty white moth(nocturnal)

*Note on caseworm:

Caseworm

Caseworm is a pest specific to irrigated rice and represents the single most destructive insect pest of rice in Sierra Leone (with the possible exception of the occasional invasions of army worms). Caseworm infestation can be extremely widespread in newly transplanted rice, and crop loss can approach 100% if control measures are not taken. The worms feed on the leaves and stems and in many cases cut off the leaf tips, resulting in a "mowed" appearance of the rice.

The worm is semi-aquatic in habit and needs to live in water order to draw in oxygen through its gills carries a water supply with it by living inside a water-filled "case" which it constructs by cutting off a leaf segment and rolling itself up inside. This case serves as a portable environment. It also do doubles as a boat: when the caseworm wants to move to another rice plant, it drops into the water and floats inside the case to a new source of food. Each caseworm attacks several plants in this fashion and constructs many cases before it is fully grown. (for control measures, see next chapter)

III. Leaf Scrapers

Green Rice Leafhopper

a) Crop Damage

Leaf scrapers are generally present in moderate numbers in Sierra Leone and habitually cause relatively minor damage. However, in certain instances they can represent a really serious threat to a crop. Leaf scraper damage occurs most frequently d ring the seedling and early tillering stages, while tie vegetative tissue is still suculent and easily attacked. As the name implies, leaf scrapers damage plants by scraping off the chlorophylcontaining layers of the leaves.

To determine the presence of leaf scrapers, look for the following signs:

- pale colorless areas on the leaf surface (where the chlorophyl-containing tic sues have been scraped off)

- presence of insects

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Crasshoppers		various sizes and markings
Epilachna, or lady-bird beetle		orange, black-spotted beetle oval, length 5-6 mm

IV. Root Feeders

Mole Cricket

a) Crop Damage

Root feeders attack the roots of the rice plant and feed on the living tissues, causing eitherstunting or death. Damage generally proves serious only during the seedling establishment and early tillering stages, when the plant's root system is just beginning to develop extensively. Root feeders breathe air and consequently are found only in plots which are not flooded. Often root feeders make their homes inside the bunds venturing forth into the plots only to feed.

To determine the presence of root feeders, look for the following signs:

- dead seedlings (no other visible damage)

- tunnel tracks in the soil leading to affected plants

-presence of insects

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Mole Cricket		brown or charcoal-gray cricket (length -to 35mm) front feet developed for tunnelling

V. Grain Suckers

Rice bug

a) Crop Damage

Grain suckers have been known to cause severe crop loss in Sierra Leone, especially in areas where continuous cropping occurs. Often the damage caused by grain suckers is not immediately apparent, since many empty grains are not discovered until harvesting has taken place and winnowing begins. Grain suckers attack the rice plant during the milk stage of the ripening phase and suck oft the liquid contents of tic grain, leaving only the empty husk.

To determine the presence of &rain suckers, lock for the following signs:

- empty grains with tiny holes bored through the husk

- erect panicles (indicating empty grains that have been sucked dry)

- presence of insects

b) Species Most Common in Sierra Leone:

Name	Nymph	Adult
Rice bug	tiny green(rice colored) also sucks sap	long, slender insect greenish-brown length 14-17 mm