What do 18-spot ladybugs usually eat?

The 18-spot ladybug is a type of 28-spot ladybug and is different from the familiar 7-spot ladybug. It feeds on aphids and spider mites and is beneficial to crops. The 18-spot ladybug is also called the potato ladybug and the Chinese lantern ladybug. Its whole body is covered with fine yellowish-brown hairs, and its body is relatively small. So what do 18-spot ladybugs usually eat? And what is the difference from the 28-spot ladybug?

1. What do 18-spot ladybugs usually eat?

The 18-spot ladybug is a pest, because its adults and larvae scrape and feed on the leaf mesophyll on the underside of leaves, leaving only the epidermis and forming many irregular, translucent, fine sunken lines, like the bottom of a sieve. They can also eat leaves into holes or leave only the veins. In severe cases, the damaged leaves dry up and turn brown, and the whole plant dies. Eggplants, fruits, and melons are often split at the gnawed areas, and the tissue becomes stiff, rough, and bitter, making them unfit to eat.

2. What is the difference between the 18-spot ladybug and the 28-spot ladybug?

(1) Potato ladybug (18-spot ladybug)

The adult is 7-8 mm long, hemispherical, reddish-brown, with dense short hairs on the back and a white reflection. There is a relatively large sword-shaped mark in the center of the pronotum, with 2 small black spots on each side (sometimes merged into 1). Each elytron has 14 black spots, and the 4 spots behind the 3 black spots at the base of the elytron are not in a straight line; there are 1-2 pairs of connected black spots at the suture where the two elytra meet. The egg is bullet-shaped, about 1.4 mm long, bright yellow when first laid, later turning yellowish-brown, and the eggs in the egg mass are arranged rather loosely. The mature larva is 9 mm long, yellow, spindle-shaped, with a raised back, and each segment on the back has black branched spines, with a pale black ring-like pattern at the base of the spines. The pupa is 6 mm long, oval, pale yellow, with sparse fine hairs and black markings on the back, and the rear end is covered by the cast skin from the larva's last molt.

(2) Eggplant 28-spot ladybug

It is similar to the potato ladybug, but the adult is slightly smaller, the pronotum has 6 black dots (sometimes the middle 4 are connected into a horizontal long spot), the 4 black spots behind the 3 black spots at the base of the elytron are almost in a straight line, and the black spots at the suture where the two elytra meet are not connected. The egg is 1.2 mm long, and the eggs in the egg mass are more densely arranged. The mature larva is 7 mm long, and the branched spines on its back are white.

(3) Damage symptoms

The potato ladybug mainly damages potatoes, eggplants, peppers, tomatoes, beans, and cucurbit vegetables, among which potatoes and eggplants suffer the most serious damage. The eggplant 28-spot ladybug mainly damages eggplants, tomatoes, potatoes, peppers, cucurbits, and other vegetables, among which eggplants suffer the most serious damage. Both ladybugs mainly damage hosts as adults and larvae. Newly hatched larvae gather on the underside of leaves and gnaw the mesophyll, leaving only the epidermis and forming many parallel, translucent, fine sunken lines, and after growing slightly larger the larvae gradually disperse. Both adults and larvae can eat leaves into perforations, and in severe cases only the thick main veins remain. In addition, they can also damage tender stems, petals, sepals, and fruits. Damaged plants not only decline in yield, but the fruit quality is also poor, and the fruits become stiff and bitter, making them unfit to eat.

(4) Occurrence pattern

The potato ladybug occurs for 1-2 generations a year in northern Liaoning. It overwinters as adults clustered in leeward, sunny mountain caves, rock crevices, tree holes, bark crevices, under stones on hillsides, in earth burrows, and among weeds. In mid-to-late May of the following year, it begins activity, first resting on weeds and small trees near the overwintering sites, and after 5-6 days, after recovering its flying ability, it migrates to potatoes, eggplants, tomatoes, peppers, and wild solanaceous weeds to feed and cause damage. Late June to early July is the peak damage period of the first-generation larvae.

Mid-August to early September is the peak damage period of the second-generation larvae. Adults rest quietly in the morning and evening, and feed, fly, migrate, mate, and lay eggs during the day, being most active from 10 a.m. to 4 p.m. Eggs are mostly laid on the underside of leaves. Generally each egg mass has 20-30 eggs, standing upright on the underside of the leaf, and each female can lay nearly 400 eggs. The egg stage varies with temperature, ranging from 5-11 days. After the larvae hatch, the first-instar larvae mostly gather on the underside of leaves to feed, and after the second instar they gradually disperse to cause damage. The larvae have 4 instars in total, and the larval stage lasts 16-26 days. After maturing, they pupate on the underside of leaves, on stems, or at the base of the plant, and the pupal stage lasts 4-9 days.

First-generation adults appear from late June to early July, and during this period the adults can again lay eggs on the underside of leaves of various hosts. Therefore, the pest population increases markedly during this period, and the damage is also obviously more serious. By early September, most second-generation adults have emerged. After causing damage for a period, in mid-to-late September they begin to seek various crevices and hide to overwinter. Adults have a death-feigning habit and a habit of eating eggs, and larvae also have a habit of eating eggs. The occurrence pattern of the eggplant 28-spot ladybug is similar to that of the potato ladybug, but the overwintering clustering phenomenon is not obvious, and adults feed day and night, with habits of cannibalizing eggs and pupae. Each egg mass generally has 15-40 eggs. Adults and larvae are photophobic and often act on the underside of leaves and in other concealed places.

The suitable temperature for adult reproduction of the potato ladybug is 22-28°C; below 15°C it cannot lay eggs, and above 35°C it gradually dies. During high summer temperatures, adults hide and rest quietly, and the infestation is more serious in fields with luxuriant branches and leaves and relatively shady conditions. The suitable temperature for adult reproduction of the eggplant 28-spot ladybug is 25-28°C, with relative humidity of 80%-85%, and when the temperature drops to 18°C it enters the overwintering state. The potato ladybug must feed wholly or partly on potatoes during its life, otherwise it cannot develop and lay eggs normally, so it can only occur in large numbers in potato-producing areas.