Management Tactics for Chilli Thrips, Diaprepes, and Flea Beetle
Chilli Thrips
Chilli thrips are the most problematic insect pests in Florida blueberry production, causing significant damage to young foliage and possibly impacting photosynthesis and plant growth. Adults are small (< 1/16 inch), with pale yellow bodies, dark fringed wings, and dark brown incomplete stripes on the abdomen (Figure 1).
The lifecycle of chilli thripshas four life stages (egg, larva, pupa and adult), and typically lasts about 18-20 days. Eggs usually hatch in 5-8 days, and two actively feeding larval instars complete their life stages in 8-10 days. Two non-feeding pupal instars complete their life stages in 2-4 days. Pupation may occur on the underside of leaves, in leaf litter, in leaf curls, or in soil. Adults live for 20-25 days.
Figure 1. Adult female chilli thrips.
Photo credits: Babu Panthi
Chilli thrips feed primarily on young blueberry foliage during summer and early fall (usually beginning in late May or early June with the first post-pruning foliar flush). Injury symptoms first appear as bronzing along leaf veins and petioles, and leaves gradually start to curl and distort (Figure 2). Heavy infestations cause leaf defoliation with extensive curling and cupping of leaves.
Figure 2. Feeding injury caused by chilli thrips feeding on blueberry leaves.
Photo credits: Babu Panthi
Scouting and early detection is essential for effective chilli thrips control. Scouting or monitoring for adults can be done by observing young leaves with a 10X hand lens, tapping young foliage onto a white sheet of paper, or using white or blue sticky cards. The appearance of bronzing on new flushes may be the first indication of the chilli thrips presence in blueberry fields.
An integrated management plan to control chilli thrips includes cultural, biological, and chemical controls. Cultural control consists of eliminating host plants (including weeds) in or near production fields that support the growth and development of chilli thrips. Using reduced-risk insecticides that conserve natural predators including Orius insidiosus (minute pirate bug), Amblyseius swirskii (predatory mites), and Geocoris spp. (big-eyed bugs) can be part of an integrated management program.
Chemical insecticides are the primary means to manage chilli thrips populations in blueberry. Reduced-risk insecticides that have shown effectiveness in controlling chilli thrips in blueberry are tolfenpyrad (Apta®), cyantraniliprole (Exirel®), novaluron (Rimon®), acetamiprid (Assail®), flupyradifurone (Sivanto®), and kaolin clay (Surround®). Spinosad (Entrust®) can be used to manage this pest in organic blueberry production. Be sure to follow all insecticide label instructions, including rotating appropriate products with different modes of action to help minimize the development of insecticide resistance.
Diaprepes
Citrus root weevil (Diaprepes abbreviatus) is becoming a significant pest on blueberry in central Florida. It has a life cycle consisting of egg, larva, pupa, and adult. Eggs are deposited by adults between two leaves, or within a folded leaf, held together by an adhesive. Adult females live for 3–4 months, during which time they can lay up to 5,000 eggs. The eggs hatch in 7–8 days, and the larvae fall to the ground, burrow in the soil, and begin to feed on the roots. Larvae are white and legless and have chewing mouthparts, reaching a length of around one inch (Figure 3). Larvae can feed on roots for several months before pupating in the soil and then emerging as adults. Adults emerge from the soil after pupating, and their scales vary in color (black with white, red orange, and/or yellow). These scales can rub off of ridge tops, leaving the appearance of black stripes on a lighter background (Figure 4). Adult weevils vary in size from 3/8 to 3/4 inch and feed on the margins of young leaves, resulting in a notching pattern. Due to this extended feeding time and the 3–4 months during which the adults are laying eggs, the timing for one complete life cycle is difficult to predict.
Figure 3. Diaprepes root weevil larvae.
Credits: Peggy Grub, USDA
Figure 4. Adult Diaprepes root weevil.
Credits: Jorge Pena, UF/IFAS
Adult root weevilsare most active from May through October or November in Central Florida, typically peaking in late May to early July. A second peak in late August to mid-October has been observed at times in citrus.
Root weevil larvae damage blueberry plants by feeding on the roots, including channeling, creating holes in the roots, and feeding injury and girdling near the crown (which can appear similar to the effects of root girdling or mechanical wounding and abrasion). These injuries can kill or cause stunting, yellowing foliage, and serious decline in blueberry plants, and may also create an entry point for Phytophthora, causing a root rot infection.
Growers can scout for adult weevils by inspecting young foliage for a notching pattern. However, because this type of damage can also be caused by other insect pests, an additional monitoring method is placing plastic sheeting or a light-colored drop cloth under the blueberry plant and shaking the branches to dislodge the adults. This will be most effective in early morning or late afternoon. There is no existing method for monitoring larvae in the soil.
Management and control should target both the adult and larval stages. Foliar insecticide sprays to control adults include imidacloprid (Provado®), bifenthrin (Brigade®), fenpropathrin (Danitol®), and thiamethoxam (Actara®). Foliar sprays should be applied every 10–14 days, and application should begin when 3 or more adults are found within 1-acre blocks. Insecticides that target larval populations are imidacloprid (Admire® Pro), Brigade®, Danitol®, and thiamethoxam (Platinum®), which are applied either by directly drenching the soil area beneath the plant canopy or by applying them through drip or micro-jet irrigation systems. Brigade® has been used in citrus as a spray application beneath the plant canopy to create an insecticide barrier to larvae dropping from plant foliage and entering the soil. Provado®, Admire® Pro, Actara®, and Platinum® are all neonicotinoids and should not follow each other in a rotation program. Pre-harvest intervals and other labeling instructions should be closely followed. Bifenthrin is not recommended to be used as a soil drench during harvest. In addition, entomopathogenic nematodes may have potential for controlling root weevil larvae in blueberry, although mixed results have been reported by growers.
Flea Beetles
The blueberry leaf beetle (Colaspis pseudofavosa) can cause serious damage to blueberry foliage during the summer months. Adults are less than ¼ inch in length, oval shaped, and shiny copper bronze or metallic blue in color (Figure 5). Leaf beetle eggs (very small and orange-yellow in color) overwinter in the leaf litter of blueberry fields. Hatching coincides with leaf bud opening, and larvae begin to feed on leaf margins, giving the leaves a notched appearance (similar to the feeding injury from adult root weevils) along with shot holes. The larval stage takes 9–20 days to complete, and larvae fall to the soil and pupate, with adults emerging approximately 15–28 days later. Adults mate and lay up to 200 eggs per female. The blueberry flea beetle has several generations per year in the southern United States.
Figure 5. Adult flea beetle
Credits: L. Buss, UF/IFAS
Chemical controls include carbaryl (Sevin®), zeta-cypermethrin (Mustang Maxx®), and acetamiprid (Assail®).
CREDIT:
DR. OSCAR LIBURD, Professor, UF/IFAS
& DOUG PHILLIPS Doug Phillips, Blueberry Extension Coordinator, UF/IFAS
