Control Methods for the Mango Leaf Gall Midge Pest

This insect is distributed in production areas including Guangdong, Guangxi, Hainan, Yunnan and Fujian, and is a frequently occurring major pest. It severely damages flush-stage leaves; each leaf may have several or a dozen galls, greatly affecting the quality of new flushes. Damaged leaves are left with numerous perforations, affecting the efficiency of leaf photosynthesis, leading to poor canopy growth and affecting tree vigour and yield.

Morphological characteristics The mango leaf gall midge (Erosomyia mangiferae Felt) belongs to the order Diptera, family Cecidomyiidae. The adult is straw-yellow, with a body length of about 1-1.2 mm. The egg is approximately oval, about 1 mm long and colourless. The larva is maggot-like and yellow; the mature larva is about 2 mm long and 0.6 mm wide, with distinct body segments and a slender sternal spatula. The pupa is short-oval and yellow, with a pupal body length of 1.4 mm, enclosed in a yellow-brown membranous cocoon.

Occurrence pattern and habits This insect has about 8 generations a year. After mid-November, larvae successively pupate 3-5 cm below the soil surface to overwinter, and emerge from the soil around early April the following year. The peak mating period is from 9-10 pm, and the next morning female insects disperse to lay eggs on the underside of tender leaves. Females die on the 2nd-3rd day after laying eggs, and males die on the next day or the third day after mating. After hatching, the larvae bite through the epidermis of tender leaves and bore into the leaf to feed on the mesophyll, causing water-soaked spots; as the larvae grow, small tumour-like galls form, with a dozen galls possible on one leaf. The damaged leaf tissue dies, and after the larvae leave the galls, the centres rupture, causing perforations. Severely damaged leaves break into an irregular network pattern, after which the older larvae enter the surface soil to pupate.

Control methods 1) Strengthen fertiliser and water management to promote uniform flushing, which helps uniform spraying for pest control during the flush stage. 2) When new flush tender leaves have emerged 3-5 cm, choose 20% fenvalerate EC or 10% cypermethrin EC or 25% deltamethrin EC at 2000-3000 times dilution, 40% dimethoate EC plus 90% trichlorfon crystal each at 600 times dilution, or 40% isocarbophos EC, 40.8% chlorpyrifos (Lorsban) EC at 1000-1500 times dilution for foliar spraying; the spray interval is 7-10 days, with 2-3 applications per flush stage. Spraying must be uniform; in spring also spray the ground within the drip line of the canopy. 3) Poison soil for insect killing. Before the spring rains arrive each year in February-March, it is recommended to use 3% isofenphos granules at 4-5 kg per 666.7 sq m plus fine sand or soil powder at 20 kg, evenly broadcast on the soil surface within the drip line of the canopy, then cover with 2 cm of soil powder. This can kill larvae that have entered the soil and adults that will emerge from the soil in spring; at this time their activity sites are limited, the population density is low and resistance is weak, so concentrated control gives better results, with a residual effect of about 60 days.