A Detailed Guide to Identifying and Controlling the 28-Spotted Ladybird Beetle on Eggplant

The 28-spotted ladybird beetle on eggplant belongs to the order Coleoptera, family Coccinellidae, also known as the groundcherry ladybird beetle, commonly called "flowered big sister." Its host crops include solanaceous vegetables such as eggplant, tomato, green pepper and potato, as well as cucurbitaceous vegetables such as cucumber. In addition, it can also damage crops such as beans, groundcherry and Chinese cabbage, among which eggplant suffers the most serious damage. It is distributed throughout the country, but occurs in larger numbers and causes serious damage in areas south of the Yangtze River basin.

1 Field identification

1.1 Damage characteristics

It damages crops as adults and larvae. Newly hatched larvae gather on the undersides of leaves and gnaw the leaf mesophyll, leaving only the epidermis and forming many parallel, semi-transparent fine grooves; after growing slightly larger, the larvae gradually disperse. Both adults and larvae can eat the leaves into holes, and in severe cases only the thick main veins remain on the leaves; the damaged leaves dry up and turn brown, and the whole plant dies. In addition, it can also damage tender stems, petals, sepals and fruits. Affected plants not only decline in yield, but the fruit quality is also poor; the gnawed parts of eggplant fruits and cucumber fruits often split, and the tissue becomes stiff, rough and bitter, making them inedible.

1.2 Morphological characteristics

The adult is hemispherical and ladybird-shaped, yellow-brown or red-brown. There are 6 black spots on the pronotum, and the middle 2 often merge into one transverse patch. The elytra are yellow-brown, and each of the 2 elytra has 14 black spots: 3 at the base, and the 4 black spots behind them are almost in a straight line. The black spots at the suture where the 2 wings meet are not connected. The dorsal surface of the wings is covered with minute short hairs and has weak gloss. The egg is shell-shaped, initially pale yellow when laid, later turning yellow-brown; the eggs in an egg mass are arranged rather densely. The first-instar larva is pale yellow, later turning white, spindle-shaped, with a raised back; each segment on the dorsal side bears neat branched spines, which are white with dark brown ring markings at the base. The pupa is pale yellow, oval, with the molted skin of the last-instar larva wrapped around the tail end, and has pale black markings on the dorsal side.

The potato ladybird beetle, also known as the 28-spotted ladybird beetle, is very similar to the 28-spotted ladybird beetle on eggplant in morphological characteristics and host crops, and each of the 2 elytra also has 14 black spots, but the 4 spots behind the 3 black spots at the base of the elytra are not in a straight line, which is a notable difference between the two. The adult of the potato ladybird beetle is slightly larger, with a relatively large sword-shaped marking in the center of the pronotum and 2 small black spots on each side (sometimes merged into 1); 1 to 2 pairs of black spots are connected at the suture where the 2 elytra meet. The eggs in an egg mass are arranged rather loosely.

1.3 Life habits

In the Yangtze River basin, it occurs 3 to 5 generations per year, and overwinters as adults under clods of soil, in bark crevices or among weeds. It is mainly scattered, with occasional clustering. After the adults emerge from overwintering the following year, they first feed on solanaceous weeds, then gradually migrate to solanaceous vegetables to cause damage, with eggplant suffering the most serious damage. The overwintering-generation adults have a long egg-laying period, so generations overlap obviously. Adults have a death-feigning habit, a certain phototaxis, and fear strong light. Eggs are mostly laid on the undersides of leaves, often 15 to 40 eggs standing upright in a mass, with a few also laid on stems and tender shoots. The dispersal ability of larvae is weak; larvae hatched from the same egg mass generally damage the same plant and adjacent connected plants. Larvae fear strong light more than adults; both adults and larvae have the habit of cannibalism and feeding on eggs. Larvae have 4 instars in total, and most mature larvae pupate in the middle and lower parts of plants and on the undersides of leaves. The 2nd, 3rd and 4th generations of this insect are the main damaging generations, and this period coincides with the peak growth period of summer solanaceous vegetables; at the end of August and the beginning of September, solanaceous crops are harvested and plowed one after another, the mortality of larvae and pupae is relatively high, and young larvae and adults move to wild hosts, beans and autumn cucumbers; in early to mid-October, adults begin to fly to overwintering sites again. The suitable temperature for occurrence is 22 to 28°C, and the relative humidity is 76% to 84%.

2 Control methods

2.1 Physical control

Taking advantage of the death-feigning habit of adults, use a container to catch them and tap the plants to make them fall for collection and elimination; this is more effective around noon. Based on the characteristics that eggs are laid in concentrated masses and the egg masses are brightly colored and easy to find, combine with farming activities to manually remove egg masses.

2.2 Agricultural control

After the crops are harvested, clean the field promptly, deeply bury or burn the remnant plants, and carry out plowing, which can eliminate eggs, larvae and adults hidden in crevices.

2.3 Chemical control

The key is to carry out control before the larvae disperse, that is, apply pesticide during the peak hatching period of the larvae or during the damage period of young larvae. The following can be selected: 4.5% beta-cypermethrin emulsifiable concentrate at 2000 times dilution, 10% bifenthrin emulsifiable concentrate at 1500 times dilution, 2.5% deltamethrin emulsifiable concentrate at 1500 times dilution, 2.5% cyhalothrin emulsifiable concentrate at 3000 times dilution, 20% fenvalerate emulsifiable concentrate at 2000 times dilution, 50% phoxim emulsifiable concentrate at 1000 times dilution, 52.25% chlorpyrifos-chlorfenapyr? emulsifiable concentrate at 2000 times dilution, and 48% chlorpyrifos emulsifiable concentrate at 1000 times dilution for comprehensive and thorough spraying, with special attention to spraying the undersides of leaves.