ACADEMICS, Biology Practical, GALMEEK NOTES AND QUIZ

Test of Practical on Grain Weevil and Rhinoceros Beetle

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August 24, 2025

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Test of Practical on Grain Weevil and Rhinoceros Beetle.

Weevils and rhinoceros beetles have short but pointed and strong mouthparts (rostrum) for boring a hole into grain.

They have chewing mouth parts.

The Life cycle of the weevil and rhinoceros beetle is a complete metamorphosis, and a larva is called a grub.

The habitat of the weevil is grains and plants that it can affect are: maize, sorghum, rice, groundnut, cowpea, cassava flour, oat, and wheat.

The rhinoceros beetle can affect plants such as oil palm, coconut, banana, yams, and beans.

They belong to a group of organisms named beetles because of;

They possess horny fore wings called elytra.
They have protruding biting/chewing mouthparts called a rostrum

Drawing of the dorsal view of *Sitophilus oryzae.*

Biological classification

Phylum Arthropoda

Reasons:

Presence of a chitinous exoskeleton
Metameric segmentation
Presence of jointed appendages attached to each segment.
Bilaterally symmetrical
Triploblastic coelomate
Open circulation (haemocilic)
Undergo moulting.

Class Insecta

Reasons:

Presence of three body divisions
Presence of a pair of antennae
Presence of three pairs of thoracic legs
Presence of a pair of compound eyes
Presence of spiracles for breathing

Order Coleoptera

Reason:

Horny fore wings called elytra. (They are modified hind wing cases that protect the hind wings.)
They have protruding biting/chewing mouthparts.
Presence of rostrum.

Observable Adaptive Features of the Weevil

Wings for flying
Rostrum for boring into grains
Chitinous exoskeleton for protection against mechanical injury and prevention of excessive evaporation of water.
Antennae for sensitivity
Can feign death when disturbed.
Small size enables them to hide among grains to be transported.
Colour to blend with its environment.

Economic importance of weevils

It destroys grains/causes post-harvest loss
It contaminates stored grain
It reduces the economic value of grains
It reduces the food value of grains
It is expensive to control weevils

Drawing of the lateral view of *Rhinoceros* *beetle*.

Economic importance of beetles

Adults and larvae attack the palm, chew flowers and fruits to prevent fruiting.
Causes pollination.
Larvae are a source of food.

Effects of the rhinoceros beetle on crop production

Chewing mouthparts chew flowers.
Pollination of flowers.

Control of weevils.

Treat stored grain with insecticides
Irradiation of stored grains
Use resistant varieties of crops
Cultural practices such as crop rotation
Isolate infected grains
Aeration of stored grain circulates air, thereby reducing the temperature, which is not conducive to breeding
Dry grains because high moisture is good for insect growth
Proper sanitation, such as sanitising bags of old seeds to prevent eggs or larvae. A dirty environment enhances the breeding of insects
Regular monitoring of stored grains

Disadvantages of control methods

The use of insecticides can cause air pollution
Can reduce food value
Can cause food poisoning

Observable Features for Feeding in weevil

Rostrum for boring a hole into grains
Chewing mouth parts for chewing food

Adaptations to escape danger in weevil

Feigning death (behavioural adaptation)
Chitinous exoskeleton (morphological adaptation)
Elytra to protect the hind wings (morphological adaptation)
Hind membranous wings for flying (morphological adaptation)

Similarities between the grain weevil and the grasshopper.

Both have;

a pair of antennae
three pairs of legs
three body divisions into head, thorax, and abdomen
a chitinous exoskeleton
a metameric segmented body
jointed appendages
compound eyes
Forewings of a grasshopper protect the hind wing and also provide camouflage
Forewings of weevils to protect hind wings
Both hind wings for flying.

Differences between the grain weevil and the grasshopper.

WEEVIL	GRASSHOPPER.
Horny fore wings	Leathery fore wings
Limbs of equal size	Enlarged hind limbs
Brown in colour	Green in colour
Small size	Large size
Rostrum present	Rostrum absent
Short antennae	Long antennae
Bent antennae	Straight antennae
Antennae end with a scape.	Absent from the scape
Elongated head	Triangular head

Similarities between the grain weevil and the soldier termite

Both have;

a pair of antennae
three pairs of legs
three body divisions into head, thorax, and abdomen
a chitinous exoskeleton
a metameric segmented body
jointed appendages.

Differences between the grain weevil and the soldier termite

WEEVIL	SOLDIER TERMITE.
Possess eyes	Eyes absent.
Small size	Large size.
Wings present	Wing absent
Rostrum present	Rostrum absent
Mandibles absent	Mandibles present.
Small head	Large head.
Brown in colour	White and brown colours.