Pest identification and understanding ecology of economically important species

Learning Outcomes:

• Describe the life cycle of the insects.
• Classify the pests into different groups based on their morphology and damages.
• Identify the pest based on their morphological features and the symptoms of the damage.

Identifying pests and understanding their life cycle and ecology (the influence of climate and other factors on their development) allows producers to take the right steps and plan mitigation strategies and, if necessary, direct control. Species of insects and mites that feed exclusively on plant food and that we find on crops are conditionally classified into three categories according to their harmfulness:

Economically important pests are species that, if we do not control them, can multiply to population levels that exceed decision thresholds and can cause economically important damage.

Secondary pests are species that are common but whose population rarely exceeds the level at which economic damage can be expected. These are usually species that are regulated by their natural enemies, so their overpopulation is usually caused by the use of some broad-spectrum insecticides that have a negative impact on their natural enemies. In this case, these pests can become problematic.

Incidental pests are pests that occur very rarely and can cause major damage once in several years, usually when extremely favorable environmental conditions prevail.

When we find an insect on a plant, we usually find only one stage of its development. It means that by this investigation we determine only a small part of its entire life cycle. Pest control is based on a tactic where we search for the "weakest link", i.e. the developmental stage that we can most easily influence. In the life cycle of pest, we distinguish the following stages:

1. Insect eggs are often a weak link, being stationary and unable to defend themselves. They are often attacked by predators and parasitoids, but direct pest control rarely focuses on eggs.
2. Insect larvae that undergo incomplete metamorphosis they resemble adult insects in appearance, lack developed wings so do not fly, and are often stationary, attached to the plant on which they feed. They feed in the same way as adults and their damage is usually greater as they are much more numerous. Because they move less (or not at all), they are often a suitable target for both parasitoids and predators. Larvae are also the most common target of control programs.
3. Larvae of insects that undergo complete metamorphosis they look completely different from adult insects and often feed differently than adults. In fact, very often the larvae are the ones that damage plants. These larvae are sometimes difficult to identify. To identify the species, sometimes it is necessary to grow them to an adult insect. As these larvae are also poorly mobile, they are good targets for parasitoids and predators, and control measures are mainly directed against them.
4. Pupae insects that undergo complete metamorphosis pass through the pupal stage. Pupal stage is stationary and during this stage insect do not take food. But significant changes take place in the pupa that lead to the development of an adult insect. Pupae cannot be actively defended against parasitoids and predators and are not a frequent target of control programs (since metabolism with the environment is minimized). Very often, the pupa is a stage where the insect spends a diapause (dormant or resting) period. Diapause occurs under conditions of low or high temperatures, depending on the species.
5. Adult insects since some of them do not cause direct damage (they do not feed on plants) and they are usually very mobile, we do not usually control them (except in exceptional cases). The use of pheromones to attract adult insects to control them is also an exception.

When we find a particular type of insect on plants, it is important to know how to determine its role in the ecosystem - what and how it feeds, and whether it is harmful, useful, or indifferent from the standpoint of cultivated culture. The role of each species in the ecosystem can be as follows:

1. Herbivorous species - feed on plants, so all pests are herbivores. But not all herbivorous species are necessarily pests, because some species feed on weeds.
2. Predators - feed on prey, usually other insect species (harmful and useful).
3. Parasitoids - lay their eggs in or on various developmental stages of other insect species (harmful or beneficial). Parasitoid larvae develop in or on a host that is not directly killed by the parasitoid, but after the parasitoid completes its development, the host dies.
4. Saprophaga - insects that feed on dead organic material of plant or animal origin. In agro-ecosystem they are useful because they help in decomposition of organic material. In commercial crops, where little organic matter is returned to the soil, they are often absent.

Accurate identification of pests is important because it allows us to make decisions about possible control measures:

1. estimate the level of population - or pest infestation - and predict the likelihood of damage and the need for control measures.
2. if the population is low, determine the monitoring method.

Because agricultural crops are attacked by a wide variety of different pests, accurately identifying them down to species level is often complex and requires highly specific knowledge. However, any practitioner must be able to identify the pest at least to the family or genus level, and this identification can then be used to surmise (depending on the host plant) exactly what species it is. After a preliminary identification of the pest, which includes an examination of the pest we found on the plant (if it was on it) or on a tool we used to hunt the pests (trappers, yellow plates), the damage is determined. All this, together with the knowledge of the most common species that occur on the cultivated crop, can allow us to accurately identify pests.

For the approximate identification of the main groups of pests, we suggest using the drawings, descriptions and photographs in Table 3.1.

Click on the images to enlarge them.

Group of the pest (family, suborder, order)	Morphological traits		Description and character of the damage		Some economically important species
	Description of the damaging developmental stage	Picture/photo	Description	Picture/photo
Grasshoppers	Grasshoppers are insects of larger size. They move by jumping with the aid of hind legs, which are longer and more developed. At the end of the back they have the ovipositor. The larvae resemble the adults, except that they do not have wings.	Figure 3.2 Grasshopper (after Schmidt, drawn by R. Bažok)	Damage is done by larvae and adults. Damage is seen as irregular bites on all aboveground plant parts (leaves, fruits). Damage is more common on vegetable and field crops.	Figure 3.3 Grasshopper damage (by R. Bažok)	Dociostaurus marocanus, Anacridium aegyptium
Mole cricket and crickets	Similar to grasshoppers but their wings are laid horizontally above their bodies.	Figure 3.4 Cricket (after Schmidt, drawn by R. Bažok)	Larvae and adults feed on plant parts. Mole crickets feed on the underground parts of the plant, resulting in plant decay. Some species of crickets lay eggs in the shoots, causing additional damage.	Figure 3.5 Molecricket damage	Gryllotalpa gryllotalpa, Oecanthus pellucens
Thrips	Tiny insects with two pairs of wings overgrown with tassels.	Figure 3.6 Thrips (after Schmidt, drawn by R. Bažok)	Adults and larvae suck on plants, most often on leaves or flowers. The consequence of the diet is the loss of chlorophyll at the site of sucking - white spots appear on the leaf.	Figure 3.7 Thrips damage (by R. Bažok)	Frankliniella occidentalis, Thrips tabaci
True bugs	Flat insects with a specific unpleasant smell. Larvae are like adults but do not have fully developed wings.	Figure 3.8 True bug (after Schmidt, drawn by R. Bažok)	The damage is done by adults and larvae by sucking on leaves and fruits (seeds). The result is deformed ears and stunted grains with poor quality and specific smell.	Figure 3.9 Eurygaster spp. damage on wheat (R. Bažok)	Eurydema oleracea, Eurydema ventrale, Eurygaster spp
Whiteflies	Tiny insects, very much alike moths but white in color. Adults are flying low above the plants. The larvae are located on the back side of the leaves, they are very small, attached to the leaf.	Figure 3.10 Whitefly (after Wyniger, drawn by R. Bažok)	Damage is done by both stages (adult and larva) but the damage from the larvae is much greater. The larvae suck on the back of the leaf. White spots are seen on the face (loss of chlorophyll). Later leaves are drying. The larvae secrete honeydew.	Figure 3.11 Damage by Whitefly (by R. Bažok)	Dociostaurus marocanus, Anacridium aegyptium
Psyllids	Gentle, tiny insects with a short and wide head and large prominent eyes. There are a small number of veins on the transparent wings. The wings have specific position above the body (like roof over the house). The larvae also have prominent large eyes. They have no wings.	Figure 3.12 Psylla spp. (after Schmidt, drawn by R. Bažok)	The damage is done by both stages but the damage from the larvae is much greater. The larvae suck on the buds, shoots and leaves, cause the leaves to curl and the attacked plant organs are covered with honeydew.	Figure 3.13 Colonies of Psyllids on plant (by R. Bažok)	DCacopsylla pyri, Psylla pirisuga
Leafhoppers	Some species are extremely large, others much smaller (up to 1 cm). When at rest, the wings are folded over the body like a roof. They are characterised by a large head and a prominent neck shield. They move around by jumping and flying. Larvae and adults have large, protruding eyes. Larvae resemble adults but do not have wings.	Figure 3.14 Leafhopper (after Schmidt, drawn by R. Bažok)	Although both stages do damage, the larvae are more harmful. The damage is manifested by sucking on plant organs. Often the plant organs are deformed, covered with honeydew, colonised by smut fungi and there is reduced assimilation. Some species are transmitting different diseases (phytoplasma, bacteria...)	Figure 3.15 Grapevine leaves damaged by Empoasca vitis (by R. Bažok)	Metcalfa pruinosa, Empoasca vitis, Scaphoideus titanus, Philaenus spumarius
Aphids	Tiny insects, which exist in winged and unwinged forms. Larvae and wingless females have no wings; they dwell in dense colonies on plants. The winged forms have two pairs of transparent wings.	Figure 3.16 Aphids (after Wyniger, drawn by R. Bažok)	Damage is caused by all developmental stages that suck on plants (mainly leaves and buds). Sucking causes leaf curling and deformation of the affected plant organs. Aphid colonies can be seen on the back of the infested leaves. They spread the viruses.	Figure 3.17 Aphid damage on sugar beet plant (by R. Bažok)	Myzus persicae, Aphis fabae, Eriosoma lanigerum
Scale insects	Harmful developmental stages are larvae, which vary greatly in shape (depending on the species). The larvae are usually attached to plant organs, usually their dorsal side of the body is hardened or covered with waxy secretions.	Figure 3.18 Scale insect (after Wyniger, drawn by R. Bažok)	The larvae suck on all parts of the plant, being most abundant on twigs and branches. When the population is high, they attack the leaves and fruits. Infested plants weaken, lose leaves prematurely, and often the infested organs are covered with honeydew, on which sooty fungi colonise, so that assimilation is reduced.	Figure 3.19 Scale insects and damage ( (by R. Bažok)	Icerya purchasi, Quadraspidiotus perniciosus, Lecanium corni
Sawflies	The damage is caused by larvae, which resemble butterfly caterpillars: they have 3 pairs of legs on the front of the body and 6-8 pairs of legs on the abdomen./td>	Figure 3.20 Sawfly larva (after Schmidt, drawn by R. Bažok)	Larvae feed on leaves by biting them into irregular shapes. In some species (apple, pear, and plum wasps) the caterpillars burrow into the freshly germinated fruit, by which they gnaw the seed and the fruit falls from the tree.	Figure 3.21 Oilseed rape damaged by Athalia rosae (R. Bažok)	Hoplocampa flava, Hoplocampa testudinea, Athalia rosae, Janus compressus
Wireworms	The damage is caused by larvae. The larvae resemble a piece of wire, are copper-brown in color, have a dark, firmly chitinized head and three pairs of legs on the thoracic segments. The first developing stadia of the larvae are whitish. They grow up to 25 or 30 mm in size (depending on the species).	Figure 3.22 Wireworms (a) after Schmidt, drawn by R. Bažok, b) photo R. Bažok)	The larvae feed on germinating seeds and the roots of germinated plants. The result of the infestation is a reduced plant population and a high number of underdeveloped plants. Damage to potatoes before sprouting shows up as holes drilled in the tubers.	Figure 3.23 Oilseed rape field (a) and potato tuber (b) damaged by wireworms (R. Bažok)	Agriotes spp.
Cockchafers	Damage is caused by adults and larvae (white grubs). Larvae are found in the soil. Larvae of May beetles grow up to a few centimeters in size. They are milky white in color, have a sinuous shape, a dark, firmly chitinized head and three pairs of legs on the chest. Adults are large insects (more than 1 cm), the body is often painted with shiny metallic colors. They have fan-shaped antennae.	Figure 3.24 Larva and adult of cockchafer (after Schmidt, drawn by R. Bažok)	The adults feed on leaves or flowers, which they destroy by biting the pistil and anthers. The larvae feed on the roots of the plants, causing decay, wilting, or slow growth of the plants. The result is a sparse crop - the damage is usually visible on a localized area in the field.	Figure 3.25 Maize field damaged by cockchafer larvae (by R. Bažok)	Melolontha melolontha, Cetonia aurata
Flea beetles	Adult insects are very small (up to 5 mm), dark body color with metallic sheen, stripes are often seen on the body. They move by jumping. Larvae are usually found in the soil, where they feed on roots, or in plants, where they feed on stems or leaf veins. They are whitish in color, have a densely chitinized, darker head, three pairs of thoracic legs, and often have sparsely distributed hairs or bristles on the body.	Figure 3.26 Adult and larva of flea beetle (after Schmidt, drawn by R. Bažok)	The damage is usually done by the adults, which make small, regularly shaped holes in the leaves of infested plants. The holes enlarge as the leaves grow. Initially, the upper or lower epidermis remains undamaged. In monocotyledonous plants, the damage is always seen in the form of streaks between the veins. The larvae feed in the stems or petioles and form galleries.	Figure 3.27 Damage caused by adults of flea beetle feeding plant leaves (by R. Bažok)	Phyllotreta spp., Chaetocnema tibialis, Psylliodes chrysocephala, Epitrix spp.
Chrysomelids	Adult beetles are vividly colored insects. The body is oval and elongate. The larvae have a densely chitinous, darker colored head and three pairs of legs on the thoracic segments. There are often bumps, warts or bristles on the body and the limbs.	Figure 3.28 Larva of chrysomelid beetle (after Schmidt, drawn by R. Bažok)	Adults and larvae feed on leaves, gnawing and causing defoliation of plants. Some larvae are feeding on roots. Feeding symptoms on leaves occur in the form of irregular corking. Due to the larger number and greater feeding capacity, larvae can cause total defoliation.	Figure 3.29 Damage caused by adults of Colorado potato beetle (a) and cereal leaf beetle (b) (R. Bažok)	Leptinotarsa decemlineata, Oulema melanopus, Phytodecta fornicata, Diabrotica virgifera virgifera
Weevils	Adults are insects whose heads are elongated into a rostrum (varying in length and width), at the tip of which is a mouthpart for biting and chewing. They are usually somewhat larger in body size, and some species are painted with shiny metallic colors. The larvae are white, slightly curved, have a densely chitinous, darker colored head, and no legs on the body. The larvae are usually found in stems, fruits or in the soil.	Figure 3.30 Adults and larva of weevils (after Schmidt, drawn by R. Bažok)	In some cases, the damage is caused by larvae gnawing on flower or leaf buds or mining in the stem. Flower buds wither. Adult feeding takes place on leaves, and damage can be seen in the crescent-shaped incisions on leaf margins. In one day they can destroy a few whole young plants.	Figure 3.31 Damage caused by weevils attacking flower buds (a) and leaves (b) (by R. Bažok)	Anthonomus pomorum, Anthonomus pyri, Byctiscus betulae, Bothynoderes punctiventris, Ceutorhynchus napi
Caterpillars	Butterfly larvae are called caterpillars. Their appearance varies from those whose bodies are covered with thick (even poisonous) hairs to those whose bodies are naked. A common feature is that we find a densely chitinized (usually darker colored) head on the body and always three pairs of legs on the chest. In the caterpillars the legs are also present on the segments of the abdomen, but their number never exceeds 5 pairs (2-5).	Figure 3.32 Caterpillars (after Schmidt, drawn by R. Bažok)	The damage is caused by caterpillars, which usually feed on plant tissue (leaves, fruits, etc.). If the stings are irregularly shaped on the surface, the leaf veins initially remain undamaged. Some species burrow into infested plant organs (fruits, leaves, cabbages). In some cases, the infested organs are covered with threads and form the thread-covered nests, which usually contain several caterpillars.	Figure 3.33 Damage caused by caterpillars on leaves (by R. Bažok)	Leaf miners, Mamestra brassicae, Cydia pomonella, Agrotis segetum, Autographa gamma
Larvae of flies	The larvae of insects belonging to the order Diptera are pale, almost transparent. They have no legs on the body. They have no distinct head. Exceptions are e.g. sciarid flies with a dark sclerotized head capsula.	Figure 3.34 Different larvae of flies (after Schmidt, drawn by R. Bažok)	The damage is caused by larvae living in the plant tissue (leaf of the fruit, stem or root) on which they feed. The damage depends on the species, the species that infest the fruits cause fruit drop and the quality of the infested fruits is reduced. In the case of vegetable flies, the infested plants rot, the development of the plants is delayed and the infested organs are deformed.	Figure 3.35 Damage caused by larva of flies on plants (a) and fruit (b) (by R. Bažok)	Phorbia brassicae, Delia antiqua, Bactrocera oleae, Ceratitis capitata, Rhagoletis cerasi
Eriophyid mites	Eriophyid mites have a narrow, elongated body brushed over the surface. They have two pairs of legs. They are small (less than 1 mm).	Figure 3.36 Eriophyid mite (after Wyniger, drawn by R. Bažok)	Nymphs and adults suck on the back of leaves, where they live in cobwebs. Eriophyid mites can be categorized according to the type of damage they cause to plants, being (1) those that form galls (gall-formers) and (2) those that inhibit the growth of new plants.	Figure 3.37 Grape leaf attacked by Eriophyid mite (by R. Bažok)	Colomerus vitis, Phyllocoptes vitis
Spider mites	Adults have an oval body shape. They are red in color. They have 4 pairs of legs. The body is covered with sparse short hairs.	Figure 3.38 Spider mite (after Wyniger, drawn by R. Bažok)	Nymphs and adults suck on the back of the leaf where they live in cobweb. The effect of sucking can be seen on the face of the leaves - on the leaves you can see small white dots that increase, the yellow leaves dry out and fall off.	Figure 3.39 Spider mite damage on leaves (by R. Bažok)	Tetranychus urticae,Panonychus ulmi