The dipteral (flies, fruit flies, leafminers, and midges) adults have only one pair of wings and have sucking mouthparts that may be modified. Their larvae are called maggots, are legless, and may lack a well-defined head capsule, with only hook-like mouthparts. The order is important in medical and veterinary entomology and include fruit flies, mosquito, house flies, horse flies and blow flies.
Bean fly (Ophiomyia phaseoli)
This is a serious pest all over the world and attacks wide range of legumes
Egg. Slender white eggs about 1mm long. Laid singly in holes made on the upper surface of the young especially at the end nearest to the petiole or on the midrib. They hatch in 3-5 days.
Larva. Small white grub or maggot which burrows down inside the stem where it feeds just above the ground level. In older plants the maggots does not move all the way down the plant. Instead it migrates to the base of the petiole where it settles down and feeds.the petioles become swollen and usually have light yellow or brown colour in appearance. The leaves often turns yellow giving a plant a droughtly appearance. The stem usually longitudinal cracks.
Pupa. Pupation takes place near the surface of the stem where the larvae have been feeding. The pupae are pupae are barrel shaped and are black or dark brown. They are about 3mm long.
Adult is a shiny black measuring about 2mm long. The total life history takes about 2-3 weeks.
The damaged plant has both destroyed stem and phloem tissues. Xylem tissues conduct dissolvedsalts and also provide mechanical support for the plant. Dissolved salts and organic materials are transported in the plant sap. Destruction of xylem and phloem tissues implies that plant sap will not be transported to the plant parts. This will in turn interfere with the plants growth. Leaves are very important organs of the plant and if destroyed especially at the base where the bean fly larvae concentrateon their feeding of leave petiole this will interfere with plant growth. The bases of the stem become thickened and cracked, many plants will die while other become stunted and yellow. Damaged can be prevented by seed dressing with aldrin and dieldrin. Early planting, crop rotation and removal of crop residues and volunteer plants are usually cultural protections
Figure 36: Damage caused by bean fly on beans
- Yellow stunted young plants
- Dead young seedlings
- Thickened and cracked stem just above the soil level
Tephritid fruit flies at present include four economically important species in Hawaii: Mediterranean fruit fly, Oriental fruit fly, melon fly and solanaceous fruit fly. The maggots infest fruits and fruiting vegetables and thus prevent many fruits and vegetables from being exportable without disinfestation treatment.
Major species of fruit flies attacking crops in Africa:
- African invader fly (Bactrocera invadens)
- Melon fly (Bactrocera cucurbitae)
- Pumpkin fly (Dacus bivittatus)
- Jointed pumpkin fly (Dacus vertebratus)
- Mediterranean fruit fly or medfly (Ceratitis capitata)
- Natal fruit fly (Ceratitis rosa)
- Mango fruit fly or Marula fruit fly (Ceratitis cosyra)
Typical host range of the fruit fly include mango, guava, sour orange, wild custard apple, wild apricot, papaya, coffee, lemon orange, avocado. Mango, however, appears to be the primary host plant.
Biology and Ecology of Fruit Flies
The morphology of the various fruit fly species is similar.
Eggs of fruits flies are small, white, and slender. They are laid under the skin of fruits in groups of 3 to 8 eggs, depending on the species. The flies lay eggs on mature green and ripening fruit. Some species may lay eggs in unripe fruitlets. Eggs hatch within 1 to 2 days.
The larvae are whitish maggots. They feed on the fruit flesh causing the fruit to rot. After 4 to 17 days the maggots leave the fruit, making holes in the skin, and drop to pupate in the soil.
The pupae are white, brown or black and 4 to 12 mm long. They are found in the soil 2 to 5 cm beneath the host plant. the flies emerge from the pupae 10 to 20 days after pupation depending on climatic conditions.
Adult fruit flies are 4 to 7 mm long, brightly coloured, usually in brown-yellow patterns. The wings are spotted or banded with yellow and brown margins.
Direct damage begins when the female fly punctures the fruit skin and lays eggs underneath it. Damage symptoms vary from fruit to fruit. During egg laying, fruit-rotting bacteria from the intestinal flora of the fly are introduced into the fruit. The bacteria multiply and causes the tissues surrounding the egg to rot. When the eggs hatch, the rotten fruit tissues makes it easier for the larvae to feed. The punctures and feeding galleries made by developing larvae provide access for pathogens to develop and increase the frit decay. Generally the fruit falls to the ground as or just before the maggots pupate.
Indirect losses: nearly all fruit fly species are quarantine pests. Indirect losses result from quarantine restrictions that are imposed by importing countries to prevent entry and establishment of unwanted fruit fly species.
Monitoring fruit flies is important to determine when they arrive in the orchard and to decide when treatment is needed. Monitoring can be done using bait traps such as the Lyn field or bucket trap (described in this datasheet under biopesticides and physical methods). For effective monitoring it is important that farmers are able to identify fruit flies from among other insects trapped.
Poorly managed or abandoned orchards can result in build up of fruit fly populations. Remove fruits with dimples and oozing clear sap. This method, although laborious, is more effective than picking rotten fruits from the ground, as the maggots may have left the fruits to pupate. To be effective this has to be done regularly (twice a week for the entire season). Kill the maggots by burning, burying or tying collected fruits in black plastic bags and exposing them to the heat of the sun for a few hours to kill the maggots. Alternatively, feed fruits to pigs or poultry. When burying fruits, ensure that the fruits are buried at least 50 cm (about two feet) deep to prevent emerging adult flies from reaching the soil surface.
Harvesting crops early when mature green helps protect some crops from fruit fly damage. Fruit flies cannot develop in certain fruits such as papaya, banana and sapodilla when they are green. Only ripe fruits are good hosts. However, in other crops, such as mango this practice is not effective as some fruit fly species like Bactrocera invadens and Ceratitis cosyra are capable of infesting even immature or green mangoes.
Biological pest control
Several natural enemies can contribute to the suppression of fruit flies. Major natural enemies are parasitic wasps (parasites the maggots of fruit flies) and predators such as rove beetles, weaver ants, spiders, and birds and bats. In particular weaver ants have been shown to be very efficient in protecting fruit trees from pests, including fruit flies. These ants prey on fruit flies, but most important their presence and foraging activity hinders the fruit flies from laying eggs, resulting in reduced fruit fly damage.Although natural enemies alone do not give satisfactory control of fruit flies, efforts should be made to protect them, and to complement their effect on fruit flies with other management options.
Tiny wasps (e.g. Bracon spp.) parasitize the maggots of fruit fly. Eggs and larvae of these parasitoids are found inside the bodies of the maggots. The parasitoid larvae are tiny, cream-colored grubs that feed in or on other insects. Adult wasps feed on nectar, honeydew, or pollen before laying eggs. Dill, parsley, yarrow, zinnia, clover, alfalfa, parsley, cosmos, sunflower, and marigold are flowering crops that attract the native braconid populations and provide good habitats for them.
Biopesticides and physical methods
To control fruitflies, a spray with a pyrethrum solution can be used. It will kill bees if they are sprayed directly, but it does not leave poisonous residues, so, the best is to use it in the evenings after most of the bees are back in their hives (after 6 pm). There is a product commercially available called Flower-DS (available at the Hygrotech Company, contact-addresses below). This product is made of natural pyrethrum and is acceptable in organic certified systems. Artificial pyrethroids will work as well if you are not concerned about organic certification, but they are stronger and will leave residues on the fruits and leaves, which are poisonous to other animals, to useful insects and to humans.
- Precautions: Be careful to spray late in the evening, follow the spraying instructions. Wear masks and skin protection. All insect poisons are also poisonous to humans even if coming from natural sources.
- Frequency of spraying: start shortly after beginning of flowering, and repeat approx every 5 days or according to counts.
- Please check the insect trap information to count your fly population. If no flies are trapped – there is no need to spray.
Frequent applications of neem can keep fruit fly attack to a minimum.
Fruit fly trap (Lynfield or bucket trap)
The Lynfield trap is cheap and easy to make. It is made of a cylindrical plastic container with 4 holes evenly spaced on its sides, a lid, a wire hanger and a bait basket (if it is to be used with a dry attractant). Similar traps can be made locally using ‘Kimbo’ or ‘Blue Band’ tubs or similar plastic containers or plastic bottles.
Leaf miners (Liriomyza spp.)
Leafminers are important agricultural pest. Two species of leaf miners have been introduced in Kenya. They include Liriomyza trifolii and L. huidobrensis. The adults are small measuring less than 2mm in length, the head is yellow with red eyes, thorax and abdomen and mostly gray and black although ventral surface and legs are yellow. Liriomyza. Trifolii is smaller than L. huidobrensis
The small adults lay eggs on plant tissues and the larvae bore into the tissues and create tunnels or mines. The tiny white eggs are inserted into upper surface of the leaf, which hatch into the larva in 2-7 days. The larva undergoes three instar stages and takes 4-7 days to fully develop. The larva are legless, white to yellow (2mm long), with dark a head. Pupae are golden brown darken with time. Pupal stage last 7-14 days and it is found in the ground beneath the host plant. Adults live for 15-30 days, female take longer than males.
The pest feed on the oviposition puncture, the larva mines the leaves .Extensive mining may cause premature leaf drop. Wounding of the foliage by larva allow entry of bacterial and fungal diseases
Detection: the leaf miner may be detected by the following
- Adults are detected flying closely around infected plants
- Presences of feeding miners
- Feeding punctures of epidermis of the leaves
- Presence of leaf miners with frass
- Larvae at the end of the mine
- Puparia on the ground beneath the plant
- Use of sticky traps
Leaf miners are Polyphagus. Their host plants include vegetables, ornamentals, legumes, flowers (roses, carnations and chrysanthemums), and fruits. They are major pests of grasshouses and protected cultivation. Leafminer attack numerous ornamental and vegetable crop plus many native species.
Management and control
Cultural control: Destruction of weeds, deep plowing of crop residues, Gamma irradiation of eggs and 1st larvae stages, remove or burn infested leaves, avoid planting alternate crops around nurseries or fields.
Biological control: Mass rearing of the parasitoid Diglyphus isae, which control the insect pest.
Pesticide control: Pyrethroids are effective in control of leaf miners. However some strains are resistant to most insecticides. Other pesticides that can be used to control the pest include imidacloprid, cyromazine and diflubenzuron (Insect Growth Regulator).
It is advisable to practice rotation among the classes of insecticides to delay the pest from developing resistance. Reduce the dosage level and frequency of insecticide application in pest control. Use of Bacillus thuringiensis is recommended for control of lepidopteran pests as it allow survival of the leaf miner parasitoids.
Midge adults are small, delicate, gnat-like flies. Midge pest include mango blossom midge, chrysanthemum gall midge, and a blossom midge on pikake, plumeria, and orchids. Beneficial flies include parasitic flies like the tachinid flies and predators like the syrphid fly larvae and aphid flies; others are important as scavengers
Dipterans insects are serious crop pests. Both larvae and adults are destructive stages in different species. Adults feed through sponging and inject their saliva onto the materials to assist in partial digestion
For more information, see here
Hutson, A.M. (1984). Diptera: Keds, flat-flies & bat-flies (Hippoboscidae & Nycteribiidae). Handbooks for the Identification of British Insects. 10 pt 7. Royal Entomological Society of London