Predatory gall midge (Feltiella acarisuga)
The Predatory gall midge (Feltiella acarisuga), is one of the effective and widespread natural enemies of spider mites Tetranychidae. Due to its ability to fly, search and predatory potential, the species is considered an important natural enemy of spider mites, in a number of crop cultivation systems. It is also known that the predator feeds on other pests, including the brown fruit mite (Bryobia rubrioculus), the red spider mite (Tetranychus cinnabarinus) and the European red mite (Panonychus ulmi). Feltiella acarisuga species can be especially useful for complex control of spider mites affecting greenhouse crops
Distribution
The genus Feltiella is practically cosmopolitan and includes 10 species: Feltiella acarisuga (worldwide, except for the Neotropical region), Feltiella pini (North and Central America, West Indies, Australia), Feltiella curtistylus (Brazil), Feltiella occidentalis (USA – California; Japan — Honshu), Feltiella acarivora (Indonesia — Java; Australia), Feltiella insularis (USA — Illinois, New Jersey, Florida; West Indies, Colombia, Argentina), Feltiella reducta (USA — New York), Feltiella ligulata (Cape Verde Islands), Feltiella kanchanjungaensis (India — West Bengal) and Feltiella tetranychi (Germany). Feltiella acarisuga is the most widespread species of this genus, which has been recorded in the USA, Canada, Finland, Germany, Great Britain, Switzerland, Italy, Morocco, Greece, Israel, India, Sri Lanka, Taiwan, Japan, and New Zealand. It is the only Feltiella species found in most of Europe and Asia.
Description
Egg: glossy, translucent, oblong eggs are laid singly, next to predatory mites, on leaves. Their size is 0.1×0.25 mm. The eggs hatch about 2.5 days after laying, and the larvae immediately begin to feed.
Larvae: orange-brown larvae vary in length from 0.2 to 2 mm during four age stages of development. They feed on mites on leaves for four to six days, depending on temperature, relative humidity and prey abundance. Larvae eat all stages of development of several species of spider mites. The population of Feltiella acarisuga larvae can reach 160 per 1 cm 2 aubergine leaves.
Pupa: A fluffy white pupa, 1 to 1.5 mm long, takes four to six days to complete development and the appearance of an adult. Pupation occurs mainly on the underside of the leaf near the vein.
Adult: Adult Feltiella acarisuga is a pink—brown fly, about 2 mm long, with long legs. Adults live for about 12-14 days, and on average one female lays about 33 eggs during her life at the rate of 3.2 eggs per day of laying. Males have a shorter life span than females. The sex ratio is approximately 1:1. Adult Feltiella acarisuga are not predators, they consume water and nectar.
Life cycle
In a climate without very dry and cold seasons, Feltiella acarisuga individuals can be observed at all stages of development throughout the year. Feltiella spp., develop from egg to egg (generation change) in 26-33 days, on average about 29 days. The development time of Feltiella acarisuga can be from two to four weeks, depending on temperature and humidity. Reproduction and development occur in the temperature range of 15-25 °C. Eggs and larvae do not survive at temperatures above 30 °C or below 30% relative humidity. For normal development, a relative humidity of at least 50% is required. The optimal combination of temperature and relative humidity is about 20 °C and 90%. However, with a large amount of prey, the level of predation remains constant throughout the temperature and humidity range sufficient for development. If the prey populations are not sufficient, then the larvae can survive by pupating in a smaller size. Larvae are also able to live for several days without prey.
Effectiveness
The Predatory gall midge Feltiella acarisuga can be used to control spider mite populations in various greenhouse and field crops, especially when it is included in the biointensive IPM program. For example, Feltiella acarisuga appeared naturally on aubergines and reduced the number of spider mites by more than 40%. Each gall midge larva is capable of eating an average of at least 15 adult mites, 30 mixed stages of development or 80 eggs per day.
In a recent laboratory study, it was reported that Feltiella acarisuga has a greater predatory ability than two predators of the Phytoseiidae mites Neoseiulus californicus and Amblyseius swirskii, on the eggs of the spider mite Tetranychus urticae. The maximum daily production of the compared individuals showed the following results. The second stage Feltiella acarisuga larva consumed 50 eggs per day compared to 25.6 eggs per day and 15.1 eggs per day consumed by female Neoseiulus californicus and female Amblyseius swirskii, respectively.
A related study evaluated a modified banker corn plant system using the spider mite Oligonychus pratensis as a victim for the spread and predation potential of Feltiella acarisuga against another spider mite — Tetranychus urticae on beans. The system showed promising results when. During two weeks of Feltiella acarisuga research, it was found that the predator flies at least 7.0 m from banker corn plants in search of new prey and is successfully installed on legumes infected with Tetranychus urticae. More than 176 larvae of Feltiella acarisuga on a bean leaf were recorded after spreading from a corn plant and proved effective in suppressing populations of Tetranychus urticae.
Weekly releases of 1,000 individuals per hectare were extremely effective for controlling spider mites on tomatoes, peppers, and cucumbers. In addition, Feltiella acarisuga (also known as Therodiplosis persicae) is used to control spider mites on strawberries and various ornamental crops. As a trial rate, it is recommended to release from 200 to 1000 individuals per hectare weekly. With a high infection, the weekly release increases by about half, 2,500 adults per ha for six consecutive weeks.
It is strongly recommended to release Feltiella acarisuga in combination with the predatory mite Phytoseiulus persimilis, a known natural enemy used to combat spider mites. Feltiella acarisuga is more mobile in adulthood than a predatory mite, and, once established, eats at least five times as many spider mites. However, Phytoseiulus persimilis should not be released where Feltiella acarisuga takes root, as they are known to eat midge eggs if prey is limited. Feltiella acarisuga is also active in cool and cloudy weather in spring and autumn. Thus, it can be used to fight spider mites in strawberries and other crops that require a low temperature to grow.
Compatibility with pesticides
It is important to avoid non-targeted side effects of chemical pesticides such as thiodane, diazinon and kelthane (dicofol); however, most fungicides can be safely used with Feltiella acarisuga. Sulphur products used in the form of dust or aerosols do not cause the death of larvae, but females avoid laying eggs on treated plants. It is reported that among the widely used insecticides in horticulture and field production, foliar application of azadirachtin, flonicamid, pyriproxyfen and spinosad, as well as pouring imidacloprid, does not have a toxic effect on the Feltiella acarisuga population (mortality <25%). At the same time, pymetrozine and buprofezin had a low to moderate effect (mortality <50%). Abamectin, bifenazate, bifenthrin, cyfluthrin, chlorphenapir, esfenvalerate, permethrin and spiromesiphene proved to be toxic (mortality > 75%) for this predator.