Lethal guest: feeding and oviposition preference of D. citri

Huanglongbing (HLB) or greening is currently considered the most serious problem in citrus farming in Brazil and the rest of the world, representing an enormous risk to the sustainability of citrus agribusiness. In Brazil, HLB was recorded for the first time in 2004, in orchards in the central region of the state of São Paulo, and today the disease is present in all other citrus producing areas.

HLB advances very quickly, with a reduction in production and, consequently, an increase in costs. Since its first record until 2011, approximately 18 million plants were eliminated in the state of São Paulo.

As there is no efficient control of the disease, HLB management is based on three measures: 1) use of healthy and certified seedlings; 2) elimination of diseased plants in orchards; and 3) control of the insect vector of the bacteria, the psyllid Diaphorina citri.

The adults of this insect measure approximately 2,8mm to 3,2mm in length and are dark in color. The young forms, called nymphs, are practically immobile, adhere to the plant (and remain there) and release a sugary substance (honeydew) that allows the development of a black fungus, known as sooty mold.

Although the psyllid causes direct damage to citrus plants by sucking their sap, the insect assumes greater importance due to the transmission of bacteria associated with HLB, whose main species in Brazil is Candidatus Liberibacter asiaticus.

There is a large number of host plants, with approximately 20 species of the Rutaceae family recorded, which include species of the genus Citrus (oranges, lemons, limes, etc.), however, not all of these plants allow the insect to fully develop. Among these hosts are also Murraya exotica, popularly known as sweet myrtle or false myrtle, an ornamental plant widespread in Brazil and around the world, being widely used as a hedge in urban areas and even close to orchards and even in cemeteries.

Several studies have shown differences in the development of the psyllid depending on the host plant, as the insects seek and choose the plants on which they feed and lay their eggs influenced by visual characteristics and odors released by the respective host plants.

 

Experiment

The present research aimed to evaluate the feeding and oviposition of the psyllid in four commercial varieties of citrus (Natal, Pera, Valencia and Hamlin).

The feeding and oviposition preference of diaphorina citri by the Natal variety, with an average of 44,6 insects feeding on the plant and 49,5 eggs laid per plant, during 72 hours, values ​​that differed from the other varieties studied.

For the feeding parameter, the Pera variety differed statistically from Valência, however, it did not present a difference from Hamlin. On the other hand, for oviposition, Pera was similar to Valencia, differing from Hamlin, which presented an average of 6,3 eggs per plant. There was no difference between the Hamlin and Valência varieties for both parameters evaluated.

According to results obtained, in a free choice test, the Natal variety was the preferred one for feeding and oviposition when compared to the other varieties, indicating the possible presence of characteristics favorable to the development of the psyllid, including tactile, visual and olfactory stimuli that should be studied in future research.

Although the results of the free choice test indicate the psyllid's preference for the Natal variety for feeding and oviposition, the material did not prove to be the most suitable when evaluating the insect's development parameters obtained in biology studies (Table 1). The variety that provided the best development for the psyllids was Valencia, in which the highest total viability was obtained, while the Hamlin variety showed less development, being, therefore, the variety least favorable to the development of the psyllid.

 

Table 1 - Means (± standard error of the mean) duration and survival of psyllids reared on different hosts

 

	Duration adult egg (days)		Viability egg-adult (%)
Varieties
hamlin	17,75 0,26 ±		32,64 5,91 ±
Pear	17,88 0,19 ±		46,97 7,63 ±
Christmas	18,43 0,13 ±		52,85 5,23 ±
Valencia	17,98 0,20 ±		65,90 6,94 ±

 

Duration

adult egg (days)

 

Viability

egg-adult (%)

Varieties

 

 

 

hamlin

17,75 0,26 ±

32,64 5,91 ±

Pear

17,88 0,19 ±

46,97 7,63 ±

Christmas

18,43 0,13 ±

52,85 5,23 ±

Valencia

17,98 0,20 ±

65,90 6,94 ±

 

Studies similar to the one reported here are unprecedented in Brazil and relevant because they record that there is an effect of citrus varieties on the psyllid and are important for creating an information base that can be used for planning and managing the pest in citrus crops. .