Оливковая плодовая муха: описание и распространение.

Species of fly

The olive fruit fly (Bactrocera oleae) is a species of fruit fly which belongs to the subfamily Dacinae. It is a phytophagous species whose larvae feed on the fruit of olive trees, hence the common name. It is considered a serious pest in the cultivation of olives. Until 1998, the fly had not been detected in the United States, and its range coincided with the range of the olive tree in the Eastern Hemisphere: northern, eastern, and southern Africa, Southern Europe, the Canary Islands, India, and western Asia. In the Western Hemisphere, it is currently restricted to California, Baja California, and Sonora. The olive fruit fly was first detected in North America infesting olive fruits on landscape trees in Los Angeles County in November 1998. It can now be found throughout the state of California.

In the final years of the 18th century, Italian scientist Giuseppe Maria Giovene (1753–1837), in his work Avviso per la distruzione dei vermi che attaccano la polpa delle olive (1792), provided some suggestions for peasants to effectively destroy the fly musca oleae, which infested the pulp of olive trees.

This species is associated with plants of the genus Olea. It is found throughout the Mediterranean basin and in South Africa. Since the late 1990s, it has also been present in California and may have spread throughout the area of olive cultivation in the Nearctic region. It is considered the most serious pest of olives in regions where it lives, significantly affecting both the amount and quality of production in most olive growing areas. The impact of its attacks tends to worsen in the more humid and cooler growing areas, with significant variations depending on the variety grown, where it affects olive cultivars and areas that have hot summers and less drought.

The egg is around 0.7 to 1.2 mm long, elongated, and slightly flattened in its stomach, with a small, white microfleece nodule, which is important for the respiration of the embryo. The larva is Caecilian and has a conical cylindrical, narrow front. It develops through three stages (larva, first, second and third stage). The mature larva is 6–7 mm long, white yellowish in colour, elongated, and subconical. The front sensors are bipolar and the second conic feature, the rear sensor, has eight sensilla. The cephalopharyngeal skeleton has very short dorsal and ventral apodemes, the hypostomal scleritis is triangular. It lacks a subhypostomal and the jaws are hooked. The oral lobes have 10–12 indents, preceded on each side by a sensory plate similar to the larva of the Ceratitis capitata. The frontal stigmas have 9–10 lobes. The three larval stages can be distinguished in different ways by their cephalopharyngeal structures. The different shapes of the frontal stigmas allow determination of the larvae of the second and third stages, while the larva at its first stage is metapneustic, equipped with one pair of posterior stigmas. The pupal stage takes place inside the puparium, an elliptical shell formed by the last exuvial transformation of the larva. The puparium is 3.5 to 4.5 mm long, varying in colour from creamy white to yellow brown, when it is dry. The change in colour of the puparium can determine the age of the pupa. Adults are 4–5 mm long. In Italy, they are easily recognized in conjunction with other Tephritidae for the small dark spot at the apex of the wing and the length of the narrow, elongated anal cell. The adult male has a hardened wing at the top of the anal cell, which is longer than the female's. The third urite shows the pectorals. The adult female has a yellowish head with two strong circular spots under the antennae close to the compound eyes, whilst the eyes are bluish green. The chest can show various specks instead of the typical bands and lines. The mesonotum is bluish gray with three blackish longitudinal lines. The humeral callus and areas mesopleurali, metapleurali, and mesoscutello are ivory. The wings are hyaline, with part of the pterostigma with brown specks at the apex. The abdomen is light brown with variable colourings: typically there are pairs of blackish spots on the first to fourth urotergit, which often come together in bands. The ovipositor is clearly visible, partly invaginated in the seventh urite, which is always black. The length is 4–5 mm. In the Asian variety, the whole body of the mesonotum is yellowish with strong, visible dark lines.

The females lay their eggs in the summer when the olive is at least 7–8 mm in diameter. Egg laying is done by making a puncture with the ovipositor into the skin of the olive, leaving only one egg in the hollow below. The bite has a characteristic triangular shape due to an optical effect. A puncture has a dark green colour, whilst older bites have a yellowish brown colour as a result of wound healing. Hatching occurs over a variable period depending on weather conditions: from 2–3 days in summer, to about 10 days in autumn. The newly hatched larva initially digs a tunnel on the surface, but later moves deeper into the flesh to the core, which is not affected in any way. During larval development, two changes occur, which in turn increase the size of the larva. Around the third change, larvae at their third stage move toward the surface and prepare the exit hole for the adult, gnawing at the flesh to leave a thin surface layer. During this phase, the olive clearly shows signs of the attack because its appears darker in conjunction with the tunneling. On the surface, a circular hole due to the remaining residual skin becomes apparent. The pupae remain dormant in the hollow below, protected within the exuviae produced by the mature larvae. At maturity, the adult breaks the exuvia and emerges from the pupa. It breaks the skin surface left by the larva by force and leaves the exit hole. In late autumn and winter, its behaviour changes; the mature larva emerges from the olive and drops onto the ground, where pupation takes place. Adults are glycogenic and feed primarily on honeydew. Since their basic diet is low in protein, they are particularly attracted to materials that emit volatile nitrogenous substances, such as bird droppings, for purposes of supplementing their protein requirements. This behavior is important because it can be used in programs for the fly's control and monitoring by using attractants such as hydrolysate proteins and ammonium salts.

Unlike other species, the succession of generations of the Bactrocera oleae is not markedly different for the scaling of ovipositioning and longevity of adults. Within a year, generally three to five generations occur, but in many years, a sixth generation can grow in the spring on the olive tree, but does not remain on the tree. The population size varies throughout the year, but with two peaks: the first in the middle of spring, at the development of the winter generation of adults, and the second, more intense, in early autumn when the olives are at the highest degree of receptivity, the temperatures drop slightly and the climate becomes wetter. In Sardinia, the larval population peaks typically occur during the months of April–May and September–October.

The damages caused by the olive fruit fly are of two types: quantitative and qualitative. From a quantitative point of view, the damage is caused by larvae of second and especially third stages, by the removal of the significant proportion of the pulp which as a consequence results in reduction in the yield of olives. Part of the production is also lost due to premature falling of the attacked fruit. Olive bites and holes dug by the larvae in the initial phase do not have a significant impact on the yield. In table olives, however, the damage extends to the sterile punctures, which cause the variation in production. A qualitative aspect to be considered is the significant deterioration in the quality of the oil extracted from olives with a high percentage of attacks by larvae of the third stage. The oil obtained from infected olives has a high acidity level (expressed as oleic acid, from 2% to 10% depending on the percentage of the infestation) and a lower shelf life as it has a higher peroxide value. Secondarily qualitative impairments of varying severity derive from the olive fruit fly attacks due to the arrival of mold through the eclosions. This deterioration in quality is evident in significantly flawed oils obtained from olives harvested from the ground or stored for several days before pressing.

The chemical battle against the olive fruit fly can be implemented against larvae by using preventive treatments against adults. The treatments are carried out by spraying the olive trees with insecticides (dimethoate, deltamethrin, and phosmet). Dimethoate is commonly used for its effectiveness and relatively low cost. It may be preferable because it would leave few residues in olive oil, since it is water soluble and would pass through the amurca. In the near future, legislative authorization for the withdrawal of use of dimethoate is to be implemented. Among the products with low impact, azadirachtin is a natural repellent extracted from the fruits of the neem tree. However, its effectiveness against the olive fruit fly has not yet been sufficiently tested. Among the organic insecticide literature, rotenone is also mentioned, but the use of this active ingredient, not readily available, must be authorized by established competent bodies after demonstrating the need for it. The larvicidal treatment is carried out according to the criteria of the scheduled pest management, pest management and integrated pest management. Scheduled pest management usually occurs with periodic preventive treatments from the period when the larvae appear during an average infestation (from midsummer in areas with higher incidence or in September in areas with lower incidence). The treatment is repeated on average every 20 days (in the case of dimethoate) or at the interval of active use. The downside to the scheduled treatment is the risk of carrying out unnecessary treatments. Pest management and integrated pest management is used if the problem exceeds the threshold. This can be estimated each week by noting the trend of the population of adults with the use of traps for monitoring or detecting the number of active infestation (bites and fertile mine of larvae I and II age). To be reliable, the system first requires a suitable response in the trial, because the intervention thresholds vary depending on the type of trap and the environment. In northern Sardinia, an intervention threshold – for cultivars of oil – was reliably evaluated, with a weekly catch of 10 adults per sticky trap in summer and 30 adults per trap in October. Further reliable information used is the sampling of olives to estimate the extent of infestation. In this case, the threshold for intervention of an active infestation is recommended between 10 15% on cultivars for oil production and 5% for table cultivars. Sampling is carried out weekly and taken randomly over a large area for an olive tree at head height. A sample is separated from samples of 100 200 olives, which are to detect the presence of live and uninfected eggs and larvae at first and second stages. The presence of eclosions, larvae and pupal third stages should not be counted because the damage has already occurred and the treatment would be worthless. The preventive treatments are carried out by spraying the olive grove with poisoned protein baits. The adults, being glycogenic, are attracted by nitrogenous substances necessary to supplement their low protein diet. The substances used as bait for the flies are protein hydrolysates and are poisoned with organophosphate insecticides (usually dimethoate). The treatment should be carried out by spraying only part of the canopy of the trees, preferably the highest point nearest the sun. The intervention threshold for adulticide treatments are quite low (two or three adults per trap per week). Recently, the introduction of ready made protein baits containing Dow Agrosciences Spinosad®biological insecticide also are authorized in organic farming. Preventive treatments with baits have the advantage of requiring lower costs and have less environmental impact, also of preventing adult egg laying and blocking the infestations directly. Generally, they are applied to only 50% of the canopy of plants, preferably facing south, with a diameter of 50–60 cm, with limited use of water. The main problem is they are not always effective. In general, the treatments with protein baits are effective in summer seasons in areas with low incidence, whilst from September–October, usually no larvicide treatments are needed. Among the recent preventive measures acquired, together with the idea of pest management and integrated pest management, the treatment with copper based pesticides has also been cited. Copper, although a pesticide, was found to exert a repellent effect against flies; the females turn their attention instead to oviposition on untreated olives. The basis for this action would be the advance biocidal effect of copper against the symbiotic bacteria, interfering with the physiology of the digestive system of the larvae. These bacteria, which appear on the surface of plants and other materials, infest adult females and transmit them to their offspring through the egg. This bacterial population would have a preferential attraction against flies, which can explain the repellent action. Repellent action would take place by kaolin, also altering the perception of the olive colour of ripening by females. Overall, these measures should not be interpreted as solution methods, including on the basis of the information on the cases, as it is still limited. Nevertheless, they are interesting because they are compatible with biological control and integrated pest management, which, therefore may play a priceless role in a strategy for integrated pest management.