Occurrence and Integrated Control Methods of the Eggplant Yellow Spot Borer

Since the 1990s, eggplant has developed rapidly in Jingning County, and the county's planting area has now exceeded 1,300 hectares, with an annual total output of more than 51,000 t. At the same time, the eggplant yellow spot borer has shown an increasing trend of damage in the county, affecting the development of eggplant production. For this reason, the author conducted a preliminary study on the occurrence pattern and integrated control techniques of this pest.

1 Occurrence and damage characteristics

The eggplant yellow spot borer, also known as the eggplant borer, belongs to the order Lepidoptera, family Pyralidae. Its larvae bore into and damage eggplant flower buds, stamens, ovaries, tender stems, tender shoots and fruits, causing branch and shoot withering, flower drop and fruit drop, and affecting yield. Although damage to eggplant fruits in early summer is relatively light, flower buds and tender shoots suffer severe damage, causing yield reduction; in autumn it mostly bores into and feeds on eggplant fruits, and a single eggplant fruit often contains 3 to 5 larvae. After the fruit is damaged, boreholes appear on the surface, and insect frass accumulates inside the fruit, seriously affecting its edible and commercial value. Damage by this pest to eggplant and other crops often results in "nine out of ten eggplants bored," with the rate of damaged fruits reaching 50% to 85%, and even in ordinary years the rate of damaged fruits reaching 25% to 35%.

The eggplant yellow spot borer occurs for 4 to 5 generations per year in this county, with overlapping generations. For early, mid-season and late-maturing eggplants, the larval damage period is generally from mid-May to the end of October. From mid-May to June, the first generation mainly damages summer shoots and eggplant fruits; from July to September, the second, third and fourth generation larvae cause the most severe damage, especially the third generation in mid-to-late August, which causes the most severe damage to autumn eggplant.

2 Life habits

In this county, the eggplant yellow spot borer overwinters as mature larvae in cocoons in the branch forks of remnant plants, among dead and curled leaves, at the root zones of weeds, and in cracks on the soil surface. Overwintering larvae begin to pupate in March of the following year, and emerge from early May to early June. Adults are active at night and hide by day, have weak phototaxis, and tend to move toward tender growth. Adults show obvious tendency to lay eggs on buds, tender eggplant fruits and tender growth, and eggs are laid singly on the backs of tender leaves in the upper and middle parts of eggplant plants, on flower buds, tender eggplant fruits and tender leaf petioles (egg: milky white when newly laid, grayish black before hatching, shaped like a dumpling, with 2 to 5 serrated projections on the ridge). Newly hatched larvae mostly bore directly from the bottom of the eggshell into flower buds, stamens, ovaries, heart leaves, tender shoots and tender leaf petioles to feed, causing flower buds and ovaries to drop (larva: young larvae are yellow-white, and when mature are mostly pink, with 6 dark brown hair spots and 2 tubercles on each segment; mature larvae are 15 to 18 mm long); third-instar larvae feed on fruits. After eggplant fruits are bored into and damaged, boreholes appear on the surface, and accumulated insect frass inside the fruit often causes rotting. After tender shoots are bored into and damaged, the upper parts die. After larvae mature, they crawl out of the damaged eggplant fruits and, at branch forks, in curled leaves, near fruit stalks, or at the edges of middle leaves in the upper and middle parts of eggplant plants, spin silk to bind a thin cocoon suspended in gaps between leaves and pupate there (pupa: light yellowish brown, body length 8 to 9 mm, pupal cocoon tough, with inner and outer layers, cocoon externally oblong barrel-shaped, grayish brown, about 35 mm long and about 5 mm wide, with an air vent at the bottom, and the eggplant yellow spot borer pupates inside the cocoon); they may also spin silk and drop to the soil surface, dead branches and fallen leaves, weeds and soil crevices to form cocoons and pupate.

It has a wide temperature adaptation range and can grow and develop at 17 to 35°C. The optimum environmental temperature is 20 to 28°C, and the suitable relative humidity is 80% to 90%. According to observations, the full generation duration of generations 2 to 4 is 32 to 51 days, of which the egg stage is 5 to 7 days, the larval stage is 10 to 15 days, the pupal stage is 10 to 15 days, and the adult stage is 7 to 12 days.

3 Reasons for heavier occurrence in recent years

(1) Suitable climate In recent years, winters have been relatively warm, which is favorable for overwintering of the eggplant yellow spot borer, and the overwintering survival rate of the pest is relatively high. May to September is the hot and humid season, suitable for the occurrence of the eggplant yellow spot borer, and is the peak occurrence period of this pest.

(2) Sufficient food The main hosts of the eggplant yellow spot borer include eggplant, black nightshade, potato, legumes and other crops. The expansion of planting area, obvious mixed planting of early, mid-season and late-maturing varieties, and large differences in sowing and fruiting across areas at different altitudes provide abundant food and favor its occurrence. In the same field, plants that grow unevenly, are shaded, and have high humidity suffer heavier occurrence.

(3) Reduction of natural enemies The natural enemies of the eggplant yellow spot borer include braconid wasps such as Apanteles and Chelonus, and birds. The parasitism rate of parasitic wasps on larvae and pupae of the eggplant yellow spot borer reaches more than 50%. However, irrational pesticide use often kills too many natural enemies and promotes the occurrence of the eggplant yellow spot borer.

4 Integrated control techniques

(1) Strengthen field management Promptly remove fallen flowers in the field, prune tender shoots of damaged plants, promptly pick off bored fruits, and carry them out of the field for centralized deep burial or burning to reduce pest sources.

(2) Trap and kill adults In areas with relatively large areas of eggplant and legume vegetables, install black light lamps, frequency vibration insect-killing lamps and the like from May to October to trap and kill adults.

(3) Chemical control Select representative type fields in the local area, conduct regular sampling surveys of the population dynamics of the eggplant yellow spot borer, and master the timing to spray promptly at the initial peak of egg hatching of the eggplant yellow spot borer. Choose highly effective, low-toxicity and low-residue pesticides. Options include 5% fipronil 1000-fold solution or 20% Ludefu 1500-fold solution or 0.36% matrine 1000-fold solution or 15% DuPont AnDa 4000-fold solution or 2.5% Caixi 1000-fold solution or 48% Lesben 1500-fold solution, used in alternating rotation, and strictly observe the pesticide pre-harvest interval. When spraying, be sure to spray evenly onto the plant's flower buds, ovaries, leaf backs, leaf surfaces and stems, with the spray liquid amount sufficient to make them wet with dripping liquid.