What are the control methods for the Oriental fruit fly (Bactrocera dorsalis)?
[Morphological characteristics]
The adult is 6-8 mm long with a wingspan of 16 mm, and the whole body is alternately dark black and yellow. The thorax has a total of 11 pairs of bristles, mostly yellowish-brown, including 2 pairs of scapular bristles, 2 pairs of dorsocentral bristles, 1 pair of presutural bristles, 2 pairs of postsutural bristles, 1 pair of mesopleural bristles, 1 pair of pteropleural bristles, 1 pair of prescutellar bristles, and 1 pair of scutellar bristles. The abdomen is oval, with 4 segments in males and 5 segments in females. The ovipositor is well developed, but its length is less than half of the abdomen, and the narrow posterior portion is shorter than the fifth abdominal segment. The egg is spindle-shaped, slightly pointed at one end, slightly curved, about 1 mm long and about 0.1 mm wide, milky white. Larva: the first-instar larva is 1.2-1.3 mm long, the second instar is 2.5-5.8 mm, and the third instar is 7.0-11 mm. The first-instar larva is semi-transparent, the second and third instars are milky white, and the mature larva after the third instar is orange-yellow. The body is conical, small and pointed at the front end, the mouth hooks are black, and the button-shaped structure on the inner side of the spiracular plate is relatively large and obvious. The pupa is oval, about 5 mm long and about 2.5 mm wide, light yellow.
[Occurrence pattern]
The Oriental fruit fly occurs in 3-5 generations per year. In areas with a distinct winter, it overwinters as pupae, while in areas with milder winters there is no strict overwintering process, and it remains active in winter. The life history is irregular, and all developmental stages often exist at the same time. In Guangdong, adults appear throughout the year, with large populations from May to October. If a citrus orchard does not retain summer flowers and fruits or mature summer oranges, and there are no nearby fruit trees such as mango, peach, pear, papaya, or guava, there will not be too many Oriental fruit fly adults in the citrus orchard before the fruit colors; however, when the citrus fruit colors, large numbers fly into the citrus orchard to lay eggs. The pre-oviposition period requires feeding on the excretions of pests such as scale insects, aphids, and whiteflies to supplement protein so that the ovaries can mature. Adults can mate multiple times and lay eggs multiple times. Eggs are laid between the segments and the peel of the fruit, and it prefers to lay eggs on ripe fruit. The oviposition puncture on the fruit is the size of a needle tip, and a gelatinous liquid is often discharged and coagulates into a milky protrusion. Using 1% red pigment, eosin, or methyl green can stain the oviposition marks. On citrus fruits picked before the eggs hatch, the oviposition holes often appear as small brown spots, which then become grayish-brown or yellowish-brown round marks. After the eggs hatch, they appear as gray or reddish-brown spots, and the internal flesh rots. The larvae gather in the fruit and feed on the juice in the segments. Although the appearance of the damaged fruit is still bright in color, the segments shrink and dry out, becoming grayish-brown, and the fruit often falls before ripening. When the larvae are mature, they bore their way out, and after leaving the fruit they jump and move about, then enter the loose surface soil to pupate.
The decomposition products of yeast and soybean after adding water have a strong attraction to both male and female adults, and methyl eugenol has a strong attraction to males. Long-distance spread mainly occurs with the movement of infested fruit. Its natural enemies include fruit fly braconid wasps, encyrtid wasps, golden wasps, and ants.
[Control methods]
(1) Trap and kill male Oriental fruit flies. In 2 mL of methyl eugenol stock solution, add 2 g of 90% trichlorfon crystals or 2 mL of 20% fenpropathrin emulsifiable concentrate, take 1.5 mL of the mixture, and drip it onto a lure core made of polyurethane foam rolled into a diameter of 1.5 cm and a length of 5 cm. Place the lure core in a trap made from a cola bottle, hang the trap in the orchard at a height of about 1.5 m with a spacing of 60-80 m, and add the attractant once every 1-2 months.
(2) Chemical spray control. During the peak period of larvae leaving the fruit and entering the soil and the peak period of adult emergence, spray the ground with 50% phoxim 800-1000 times dilution; during the main damage period, spray the canopy with 80% dichlorvos emulsifiable concentrate or 90% trichlorfon crystals or 50% malathion emulsifiable concentrate 800-1000 times dilution.