Lobesia botrana in grapes, plums and blueberries: biological behavior, damage symptomatology and analysis of critical points

An increase in moth populations has been observed based on catches in pheromone traps. "This sustained increase in Chile endangers other alternative hosts, so the industry has to take some preventive actions at the garden level and even packing, through quality control. In fact this season we started with a preventive program in cherry orchards ", says David Castro.

The 1 graph shows the total catches in vines of four successive years, since it has been determined that there are three flights per season. The first in October, the second in December and the third in February. "The strange thing is that when control is made of the first flight, the winter's departure, a positive result is achieved and the populations go down (on the second flight). But a rebound effect is observed since the curve of the third flight is always higher "says Castro. "This is explained, he continues, because in the first flight the development of the plague is slower and therefore there is more time to correctly carry out the control applications. On the second flight, the development time is shorter, so the window available is smaller and requires more precision ". Although it indicates that there may be other factors that affect the increase of the third flight, the important thing is that this population is the one that will appear on the first flight of the following season. "As long as we manage to reduce the number of males on the third flight, we will be able to assume that we are succeeding in time", Señala.

In the last season the pattern was repeated exactly as it has been observed the last 4 years. "A large first flight and then decrease the population on the second flight, which gives to think that it is being properly controlled, but then - despite that - there is a population increase on the third flight"says the professional.

Recognition and biological data of Lobesia botrana

Thanks to the accumulated experience, both in the field and laboratory, in the last 4 to 5 years we already know more about the behavior of the pest in the conditions of the different regions of Chile.

The different stages of development of the pest, photo 1, correspond to egg: yellow egg and black head egg (0,9-0,8 mm); then 5 larval stages follow: L1 (1,9-1,5 mm), L2 (1,9-3,0 mm), L3 (4,5-5,0 mm), L4 (6,0-7,0 mm) and L5 (10,0-11,0 mm); the pupae of female and male (5,0-6,0 mm), which corresponds to the wintering state; and the adult (6,0 mm).

Within the five larval stages, the smallest larvae measure about 1 mm to end up being a larva of 1 cm. In the 2 photo larvae are presented in the different stages to appreciate the differences between them. As already said, the times that the larval developments take are different, in the second flight the development is faster than in the first and in the third it is relatively similar to the first.

The main factor that governs the development of the pest is the climate, both temperature and photoperiod are fundamental. "This moth under sustained temperature conditions of 23ºC, in just two days manages to mature sexually, copulate and oviponer. This corresponds to data that we have collected in the field and that we have observed in the laboratory. But with only 14,5ºC of sustained temperature, the same process can take 7 days. It is important to know these dynamics and above all to know how adults work because in the future that understanding can give us more precision in the control ", warns Castro.

Other important information that is given is that the minimum temperature required for copulation is 13,5ºC, while the oviposition occurs with a minimum temperature of 9,0ºC. Regarding the fecundity potential, the female of this moth manages to put 196 eggs at 23ºC while the literature mentions a potential superior to the 200 eggs. This indicates a great potential to produce individuals and multiply. On the other hand, the fertility potential at 23ºC is between 85 and 90% hatching. That is to say, of the 85-90% of the total eggs that the female is going to come alive larvae.

"At 23ºC adults live 12 days but the reality is that they can last up to 20 days since we have seen that at temperatures of 14,5-16ºC can increase their longevity. We have also observed that if the female does not like the surface available to lay the eggs, the moth is able to retain them, wait and increase their longevity until they find the ideal place to lay the eggs "He says. 

Deadly temperatures have also been determined, "What is very important to consider in order to develop a system approach, which consists of actions for the management of pests. Something that we have been investigating together with SAG and ASOEX ", anticipates the professional.

"This, he continues, is an interesting element because in the chain you can place an important element of mitigation and with this we know that naturally at 0ºC for 15 days we can achieve a mortality from 99 to 100% in eggs and larvae".

The summer diapause can explain the peak of the third flight

The stages of development that are induced to winter diapause correspond to eggs and larvae from 1 to 3. That is, "When the autumn approaches the stages that go between the egg and the larvae until the third instar (L3) are going to be induced to winter as pupa. The following stages, fourth and fifth instar (L4 and L5), although they begin to shorten the days, these will continue their development so that until May it is possible to see some moths flying ", he says. To those David Castro he calls them suicidal moths because there is no longer any substrate to feed on.

"Another interesting phenomenon, the expert points out, that we have detected in the field is the summer (summer) diapause. That is, if all temperature conditions are given throughout the day, the larva has no problem remaining as a pupa. We calculate that more or less one 7,7% of the first generation remains in a state of summer diapause whereas an 13,5% of the individuals of the second generation can remain in that state. Subsequently, the third flight occurs and it is when the summer diapause can explain the rebound effect by which this peak of the third flight is higher than the second (the number of captures and therefore of individuals that fly is greater). ". The percentage of emergence of the pupae after the summer diapause is 80%, which was determined based on the observation of 1.500 pupae.

It is possible to observe cocoon differences between a diapaused pupa and one that will follow its normal cycle (photo 3). "The pupa on the left has a cocoon shell which allows it to go through diapause without becoming dehydrated, one of the reasons why a large number of the moths emerge on the following season"He says.

Symptoms of damage in table grape

The 4 photo corresponds to a larva L1 or first instar. It highlights the jaws that this larva has since birth, which are large enough to break the surface of the fruit. "Many of the photographs we have are the result of the experiences obtained thanks to the Corfo and FIA projects. These photographs can be useful to those who work in the field to identify the damage and the plague "He says.

5 photo shows a black head egg deposited in a grape berry of the Crimson seedless variety. Likewise, the marks of hatched eggs can be observed on the surface. The egg measures barely more than 0,5 mm but these eggs shine with light, which allows them to be found in the field.

In the 6, 7 and 8 photos you can see some of the first perforations. The first perforations are less than 0,3 mm so they are almost impossible to observe with the naked eye. However, according to David Castro, with the experience that is acquired in the field, the view is refined. In the case of the berry with four perforations, these are caused by a single larva. When it leaves the egg, the larva first explores, generating several bites until it decides to enter. "It is not that the four perforations, although they have different sizes, indicate the presence of four larvae. The larva does not leave the berry since it remains in the fruit feeding to continue developing ", clarifies.

The larva continues to grow, continues to feed and each time the bites are larger, which can finally trigger gray rot problems (Botrytis cinerea). At this height it is quite larger larvae so the damage is easier to detect.

Analysis of critical points

This analysis of critical points comes from the experience with Korea and is of interest for a future System Approach with the USA. Affirms the professional: "It is important that in the future we have a System Approach for table grapes to the US so the plague must be handled at levels as low as possible. In the case of Korea, for example, 300 should be checked for clusters to see if they are carriers of the pest and we hope to have a similar system for the US in the future ".

Farmers must be concerned about their environment, Castro advises, among other things who they are and what their neighbors do. In the photo 12 it is seen that the property in question (red perimeter) is surrounded in almost all its perimeter by apple trees, pear trees and kiwi. But below in the photo (to the East of the property in question), there is a vineyard, that is, an estate where grapes are grown for winemaking. The four green points, all on the perimeter, represent the places where the immature stadiums were detected. That is to say, "The greatest risk is on the banks of the orchards and this is based on the fact that this plague flies up to 200 meters according to what is found in the literature. If necessary, it is advisable to apply two or three times along the edges of the farm to avoid the presence of a live larva. You have to think that it is enough to find an egg, which measures almost nothing, or a very small larva, so that the garden is objected and the fruit must be fumigated ", warns the agronomist.

In the other case, photo 13, again the green dots represent the places where the larvae were found. "In the exploration for Korea we reviewed around 200 fields and found that in a large percentage the detections related to neighboring sites", concludes the FDF specialist. 

It is key to know the characteristics and behavior of the pest in each of its stages of development. It is also to follow all the procedures defined by the protocols that involve the fruit trees under mandatory control, both in the containment and eradication areas. But it is also key to anticipate potential problems in other fruit species, the so-called 'bibliographic hosts', among which the cherry tree stands out. Also know the neighbors well, worry about the environment of the orchards and strengthen the chemical control of the perimeter of these, especially when a vineyard is located less than 200 m away from its land.

Japanese plum

Artificial infestation in field cages var. Angelene

The plum trials were done because Mexico requested that it be studied whether the plum acted as a host of Lobesia botrana. In the left photo you can see the eggs, in the central photo an hatched egg and in the right photo a larva that has remained on the surface of a plum.

Blueberry Damage

Larvae come out of the eggs in the blueberries that immediately try to penetrate the fruit. The larvae always look for protected sites so, for example, at the points where the fruits come together are potential places where the plague is hidden. As seen in one of the photos, the larva can also bite superficially and not necessarily immediately penetrate the fruit. 

In the photo on the right below you can see the perforation, the larva and the cranberry symptomatology. Dehydrated fruits are observed, of a darker color and therefore it is possible to appreciate a contrast.

Summary biological data (Based on experience in the field and laboratory)

• Minimum time for sexual maturation, copulation and oviposture = 2 days (23 ° C) and 7 days (14,5 ° C)
• Minimum temperature required for the coupling = 13,5 ºC
• Minimum temperature required for oviposture = 9,0 ºC
• Fertility potential (Tº 23ºC) = 196 eggs / female
• Fertility potential (Tº 23ºC) = 85 to 90% hatching
• Longevity of adults (Tº 23ºC) = 12 days
• Lethal temperature: 0ºC for 15 days = mortality of 89% to 100% eggs and larvae
• Development stages that are induced to winter diapause = Eggs, L1 to L3
• Summer diapause (summer): 1st generation = 7,7% and 2nd generation = 13.5%
• Emergency potential from pupated pupae = 80% (n = 3.500)

Source: Redagrícola

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