Control Methods and Technical Key Points for the Lychee Stink Bug

The lychee stink bug (Tessaratoma papillosa), belonging to Hemiptera, Pentatomidae, is a major pest of longan in our region. Both adults and nymphs pierce and suck the sap of tender shoots, flower clusters and young fruit; the damaged parts become discolored and dry up, causing flower and fruit drop. When disturbed, the foul liquid it emits touches tender leaves, flowers and fruit, causing burns and scorching; the fruit shell turns scorched brown, seriously affecting longan yield.

The lychee stink bug has 1 generation per year, overwintering as sexually immature adults on the undersides of leaves in wind-sheltered, sunny or dense foliage, or in tree holes and rock crevices. In spring of the following year, when the temperature reaches about 16°C, it begins activity and prefers to gather on trees with abundant flowers and leaves to feed; April is the peak period for mating and egg-laying. Eggs are mostly laid on the undersides of leaves in the lower canopy; each female can lay eggs 5--10 times on average, up to 17 times. Most egg masses contain 14 eggs, arranged in a cluster. After Qingming, nymphs hatch successively and pierce and suck the sap of tender shoots, flower clusters and young fruit, often causing flower and fruit drop; after June, mature nymphs successively emerge as adults, and adults prefer to feed on tender shoots and fruit clusters.

The most critical periods for pesticide application are two. First, in early spring when overwintering adults begin activity, that is, mid-to-late March, when adults are about to lay eggs and have the weakest resistance to pesticides; at this time, killing adults with pesticides can significantly reduce the population base and is extremely favorable for control throughout the year. Use 90% crystalline trichlorfon at 500--800 times dilution, or miechongling emulsifiable concentrate at 1500--2000 times, or pyrethroid pesticides (such as cypermethrin, deltamethrin, permethrin, etc.) at 1500--2000 times, applied 1--2 times.

Another suitable control period is mid-to-late May, when eggs have largely hatched into the nymph stage; 1st--2nd instar nymphs have a thin wax layer on the body surface and a low degree of cuticularization, making them more sensitive to pesticides. Use 20% fenvalerate at 5000 times plus 40% omethoate at 1000 times, or 4.5% high cis-trans cypermethrin at 2500--3500 times for a good control effect.

The best time to apply pesticides is in the morning or evening when there is no dew; at this time the temperature is lower, the stink bug's death-feigning behavior is more pronounced, its activity is weak, and it is easily exposed to the pesticide. Where conditions permit, orchards can manually remove egg masses and kill nymphs from March to May. They can also release Anastatus japonicus and the lychee stink bug fungus to parasitize the eggs of the lychee stink bug. Before releasing wasps in mid-to-late March, first check the stink bug density on the trees once; if each tree has 150 stink bugs, wasps can be released; if it exceeds 150, first spray trichlorfon once to reduce adult density, then release the second batch of wasps after 5 days, which can reduce damage from overwintering old adults.