Plant husbandry – Cover – shade – or screen – Netting – open weave – mesh – or foraminous type
Reexamination Certificate
2002-12-05
2004-09-28
Nguyen, Son T (Department: 3643)
Plant husbandry
Cover, shade, or screen
Netting, open weave, mesh, or foraminous type
Reexamination Certificate
active
06796083
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates generally to the field of agriculture and horticulture and, more particularly, to a barrier, enclosure and method designed to protect plants and crops from infestation by insects, particularly
Thysanoptera thripidae
, also known as thrips.
Thrips are distributed worldwide and are important crop pests and vectors of viral diseases. Damage to commercial crops from thrips is estimated worldwide in the tens of millions of dollars per year.
The word Thysanoptera comes from the Greek ‘thysanos’, meaning a fringe, and ‘pteron’, meaning a wing. Accordingly, thrips are highly mobile fringe-winged insects. There are presently at least 6,000 active species of thrips in the world.
Thrips are very small, elongate, cylindrical, gregarious insects ranging from {fraction (1/25)} to ⅛ inch in length. Males are usually smaller than females. The nymphs are frequently pale yellow and highly active. The antennae and legs are relatively short. Adults are usually black or yellow-brown, but may have red, black or white markings and often jump when disturbed. They may have wings or may be wingless. If wings are present, they are long, narrow and fringed with hairs. Winged varieties often ride air currents in order to disperse widely, having a predisposition towards thunder storms as a suitable time of flight. Hence, they are referred to as ‘Thunder flies’ or ‘Thunder Bugs’ in some locations.
Thrips have asymmetrical mouthparts, having only one (the left) mandible, short 6 to 10 segmented antennae and no cerci. Their wings when present are nearly equal, very thin with little venation and a lot of hairs making a fringe around the edge which greatly increase the effective size of the wings. Fully winged, brachypterous (with reduced wings) and apterous (wingless) forms may occur in the same species.
Thrips mouthparts are designed for piercing and sucking. Most species feed on plant sap. To obtain sap, a thrips will make an incision in a single cell with the left mandible and then insert the maxillae and hypo pharynx and pump out the juices of this and adjacent cells using a pharyngeal pump.
Thrips breeding inflicts further damage on plants. Females of some suborders are equipped with ovipositors which are used to cut slits into plant tissue into which eggs are inserted. Females of other suborders lack ovipositors and lay their eggs on the outside of plants, either singly or in small groups.
Thrips undergo gradual metamorphosis. A typical thrips life cycle is as follows. Each female lays 25 to 50 eggs which hatch in two to seven days into active nymphs. Parthenogenesis (where ova develop and mature into female nymphs without fertilization) occurs in many species. Nymphs resemble adults, but lack wings and are lightly colored. The nymphal stage is followed by two resting stages: the prepupa and pupa. The resting stages can be found either on the host plant or in the soil below the host plant. Under favorable conditions, the developmental period from egg to adult ranges from eleven days to three weeks depending on the species. Hence, a population may increase quite rapidly.
The Onion Thrips and the Western Flower Thrips are the most crop-damaging species in the U.S.A., Europe and the Middle East, both for the damage caused by their eating and reproductive behavior and because they are known vectors of plant diseases, the most important of which for greenhouse crops are impatiens necrotic spot virus and tomato spotted wilt virus. When thrips feed on plants infected with these diseases, they transmit the diseases to other plants in the greenhouse. Once plants are infected, it is too late to do anything except dispose of diseased plants.
Tolerance of thrips on floriculture crops is particularly low, as thrips infestation results in deformation of flowers and leaves. Flower buds often abort in heavy infestations. Thrips feed on both foliage and flowers, as well as young tissues in shoot apexes where the leaves are expanding. By puncturing the plant and withdrawing cell sap, they cause bleached, silvered or deformed leaves and necrotic spots or blotches on flower petals. Eventually the damaged foliage becomes papery, wilts and drops prematurely. In addition, thrips produce large quantities of a varnish-like excrement which collects on leaves, creating an unsightly appearance.
Thrips are one of the most difficult pests to control in greenhouses. They are tiny insects that reproduce rapidly, eat voraciously and can easily and swiftly devastate an entire crop. Accordingly, many different practices are presently in use to prevent or control thrips infestation. Control measures to date include biological measures such as the introduction of predacious insects. For example, adult female predatory mites (Neoseiulus) consume from 1 to 10 young thrips per day and have a 30-day lifespan. Adult pirate bugs (Orius) consume 5-20 thrips (all stages) per day. Orius is the only predator that attacks thrips in tight places like flower buds. Soil-dwelling predacious mites (Hypoaspsis) attack thrips in their pre-pupal and pupal stages when they inhabit the soil or growing medium.
Thripobius semiluteus
is a parasitoid of thrips nymphs.
Also in limited use are cultural controls, such as providing a fallow period in summer by removing all plants and heating the greenhouse until soil temperatures reach 60° F. for three weeks. During this time, thrips eggs will hatch and the nymphs will starve for lack of food. Another cultural control is to remove all flowers and buds, if not crucial to the crop. A further cultural measure is to introduce plants, such as garlic, that repel thrips.
There are many different pesticides in use, including “biorational” pesticides, which are used by growers relying on organic pest management. However, thrips control is difficult with the use of pesticides, as during much of their life cycle thrips exist as eggs, as pupae in the soil, or as extremely mobile adults. Once thrips infest a crop, the adult females begin feeding and laying their eggs. Thrips usually concentrate on rapidly growing tissues such as young leaves, flowers and terminal buds. This affinity for tight places makes thorough coverage with a pesticide difficult.
Agricultural researchers have experimented with other measures to repel thrips by interfering with their visual cues with limited success. Reflectance of visible light was found to repel xanthophyllous thrips from the surface of certain colors, as described in an article by Matteson, N., Terry, L (1992).
Response to color by male and female Frankliniella occidentalis during swarming and non
-
swarming behavior. Entomol. Exper. App.
63:187-201. Apparently, thrips are more attracted to some colors than to others. This research does not, however, demonstrate a repellant property of any particular color other than relative to other colors.
The use of UV absorbing materials has been found to be of assistance in repelling crop-damaging insects and is in use in commercial growing of field crops. UV absorbing screens and films are used as roof coverings in conjunction with wall coverings of conventional insect-excluding netting. This phenomenon is discussed extensively in a recent professional publication: Antigenus, Y., Lapidot, M., Hadar, D., Messika, Y, Coen, S. (1998).
Ultraviolet
-
absorbing screens serve as optical barriers to protect crops from virus and insect pests. J. Econ. Entomol.
91: 1401-1405. The studies were not conclusive, however, in demonstrating a repellant effect as opposed to a camouflaging property and it is conceded in this publication that such films and combinations of films and nets do not provide totally effective exclusion unless the nets have a mesh size that is sufficiently small to constitute a physical barrier.
Further attempts at visual manipulation include the use of reflective colored mulches around the base of plants. These measures were also shown to reduce thrips infestations and tomato spotted wilt virus incidence in crops, as described in the aforecited articles by Brown
BiotechNet Ltd.
G.E. Ehrlich (1995) Ltd.
Nguyen Son T
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