Green onion horse
Thrips tabaci, also known as the onion thrips or tobacco thrips, is a common pest belonging to the order Thysanoptera and family Thripidae. This tiny insect poses a serious threat to a wide range of crops, including onions, garlic, leeks, and other vegetable plants. Its feeding activity can cause significant damage, reducing both yield and quality.
**Damage Symptoms:**
The adults and nymphs feed on the tender parts of plants such as the heart buds, shoots, and leaves of onions and leeks. Infested leaves develop long white streaks, and in severe cases, the leaves become curled, yellowed, and distorted. The damage not only affects the plant's appearance but also its growth and productivity.
**Morphological Features:**
- **Adults:** Measuring 1.1–1.3 mm in length, they are light yellow to brownish in color, with purple compound eyes.
- **Nymphs:** Initially white when newly hatched, they gradually turn yellow to dark yellow as they mature.
- **Eggs:** Small, kidney-shaped, and about 0.2 mm in length, laid just beneath the epidermis of the host plant.
**Life Cycle and Habits:**
Thrips tabaci can complete six to ten generations per year, depending on environmental conditions. Adults, nymphs, and pupae overwinter in onion or garlic sheaths, weeds, or in the soil around the host plants. In spring, as green onions and garlic start growing, the thrips begin feeding and then spread to other hosts. They are particularly damaging to garlic in early spring and to onions during late summer, with peak infestations occurring between July and August.
These pests are highly mobile, capable of flying and jumping, and can be carried by wind or water. They avoid strong light and tend to congregate in shaded areas. On cloudy days or during early morning and evening, they are more active on the surface of the host plants. Most of the population consists of females, as males are rarely observed. Female thrips reproduce through parthenogenesis, laying up to 50 eggs on average, with some reaching as high as 171. Their lifespan is about 8–10 days, and eggs hatch within 6–7 days during May and June.
The nymphs go through four developmental stages, with the third instar burrowing into the soil before pupating. After emerging from the pupal stage, they become adults.
**Environmental Preferences:**
Thrips thrive in warm, dry conditions, with an optimal temperature range of 23–28°C and humidity between 40–70%. High humidity (100%) combined with temperatures above 31°C can be lethal to nymphs. During rainy seasons, excessive moisture between onion leaves can drown the nymphs. Additionally, heavy rain or irrigation can lead to soil compaction, preventing nymphs from entering the soil and hindering adult emergence.
**Control Measures:**
To manage thrips effectively, several strategies can be employed:
1. Remove dead or infected leaves from the field to reduce overwintering populations.
2. Apply insecticides during the nymph stage for better control. Recommended options include:
- 40% Qixingbao EC diluted 600–800 times
- 21% Killer EC at 1500 times
- 50% phoxim EC at 1000 times
- 20% chloral EC at 2000 times
- 10% imidacloprid wettable powder at 5000 times
- Pyrethroid-based pesticides can also be used.
Other effective options include 20% compound Liuyangmycin EC at 1000 times, 80% Bataan WP at 2000 times, and 25% synergistic quinolone EC at 1000 times.
These treatments should be applied every 7–10 days, with 2–3 consecutive applications for best results. It is important to stop pesticide application at least 7 days before harvest to ensure food safety.
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