Monitoring of three Hoplocampa saw ﬂ y species in plum orchards

Three sawfly species ( Hoplocampa minuta, Hoplocampa ﬂ ava, Hoplocampa fulviicornis ) have been monitored in plum orchards during the ﬂ owering period in three consecutive years at three different locations in Hungary using chromotropic white sticky traps. Black and yellow saw ﬂ ies ( H. minuta and H. ﬂ ava ) are one of the most important pests in plum orchards, however plum-fruit saw ﬂ y ( Hoplocampa fulvicornis ) has not yet been documented from plum orchards in Hungary. In almost all locations and years, H. minuta was the most dominant species, except in Cegl (cid:1) ed, 2014, where H. ﬂ ava was the most abundant one. In terms of sex ratio, in all three species, more males than females were caught in the traps except in 2016 at (cid:1) Erd, where more H. ﬂ ava females ﬂ ew into the traps.

H. minuta and H. flava are univoltine, monophagous species, often co-occur in plum orchards and feed exclusively on plum fruits.After emerging and mating, during the plum flowering period, the fertilized females insert their eggs into the calix of the flower using their saw-like ovipositor.Parallelly with the fruit development, the larvae hatch and enter into the fruit.One sawfly larva can damage up to 6 fruits, which increases the damage level of these pests.Unripe fruits fall to the ground due to the damage.In organic and non-treated orchards, the yield loss can vary between 36 and 96% (Caruso and Cera, 2004;Rozpara et al., 2010).So far only chemical treatment is available to control this species.The insecticide application has to coincide with the petal fall of the flowers.However, at this time several bees and other beneficial insects are present in the orchard feeding on the residual flowers, which can be harmed by the insecticides.The most important aim of integrated pest management (IPM) is to spatiotemporally predict the existence of pests to determine efficient insecticide delivery timing (Lefebvre et al., 2015).So far only the chromotropic white sticky trap is available to monitor the flight activity of these two sawfly species in plum orchards (Blaisinger, 1975;Tamo si unas et al., 2014).Although H. minuta and H. flava are present in Hungarian plum orchards, little is known about their populations' size, flight dynamics and distribution of the different species.
This study aimed to monitor the flight activity, species and sex ratio of Hoplocampa species during 3 years in three different locations in Hungary using chromotropic white sticky traps.

MATERIAL AND METHODS
The field trapping experiment was carried out at three different locations in Pest county, Hungary: 1.At Cegl ed in the plum GenBank orchard located at the Research Institute for Fruitgrowing and Ornamentals (47809 0 51.2 00 N 19850 0 08.2 00 E) in 2014 between March 27 and April 26.This orchard contains more than 200 different plum varieties with different flowering times.P. spinosa was not found near the orchard.During the experiment, the plum trees were not treated with any insecticide.

At
Erd in a non-cultivated plum orchard (47820 0 47.7 00 N 18851 0 34.2 00 E) in 2015 between March 31 and May 04, and 2016 between March 29 and April 22. P. spinosa may have occurred nearby this orchard, however, we did not conduct any survey on it.This orchard had no insecticide treatment.
3. At Pom az in a cultivated plum orchard (47865 0 52 00 N 18898 0 77 00 E) in 2015 between April 07-23.As far as we know P. spinosa did not exist near the orchard.During the experiment, this orchard was not treated with any pesticide.
In all three orchards, the stock of the plum trees was myrobalan plum (Prunus cerasifera).At Erd and Pom az, besides the cultivated plant varieties, the wild type myrobalan plum was also found.This plum tree starts the flowering period a couple of days earlier compared to the cultivated varieties.
The white sticky traps (CSALOMON ® PALf) were provided by Plant Protection Institute, CAR, ELRN (Budapest, Hungary) and placed out in plum orchards at the three different locations.At all locations, 4 traps were placed out.The traps were hung on the plum tree branches at 1.5 m above the ground.The traps were 10 m apart from each other.New traps were placed out at every inspection time.Traps were brought to the laboratory where the specimens were identified, sexed and counted by using a stereomicroscope.To separate H. minuta and H. fulvicornis, we used the morphological identification key published by Nagy (1960).H. minuta has 4-5 mm, while H. fulvicornis has a 3 mm body length.The whole body of H. minuta is black, however, the color of the clypeus, tegula and the distal part of the abdomen are brownish or yellowish of H. fulvicornis.H. minuta has a brow stigma, however, H. fulvicornis has a yellowish one.H. minuta males have yellowish-brown antennae, while H. fulvicornis males have a yellow one.

RESULTS
The average trap catches of the three different species varied between the experimental years and locations.In 2014, at Cegl ed first adults appeared in the traps on March 27 (Fig. 1A and B) and H. flava was the dominant species (Fig. 1C).At this location, traps did not catch any H. fulvicornis.The highest trap capture of H. flava was on April 04, on this date the males were dominant (Fig. 1B).Interestingly, more females than males of H. minuta flew into the traps (Fig. 1A).
In the year 2015 at Pom az, the trap caught the first adults on April 10 (Fig. 2A, B and C), in the same year at Erd the first adults were caught ten days earlier, on March 31 (Fig. 3C).In both locations, H. minuta was the dominant species.At Pom az the highest trap capture of this species was recorded on April 13 (Fig. 2A); however, in the same year at Erd, the traps caught the highest number of H. minuta four days later on April 17 (Fig. 3A).It is important to note that both locations traps caught a third species, H. fulvicornis (Fig. 2C and 3C).Also, at both locations this year, traps captured more males than females of all three species (Fig. 2D and 3D).
In 2016 at Erd, the traps caught the first H. flava adults on March 29 (Fig. 4B).H. minuta was the most dominant species and the highest trap capture of this species' males was recorded on April 08 (Fig. 4A).On April 15, traps captured slightly more H.flava females than males (Fig. 4B).In this year, traps also caught both males and females of H. fulvicornis (Fig. 4C).

DISCUSSION
In this study, we monitored three different Hoplocampa species in three different locations of plum orchards in three consecutive years using white, sticky chromotropic traps.Because H. minuta and H. flava are one of the most important pest species in the plum orchards in Europe (Caruso and Cera, 2004), monitoring the population of these species is important in terms of the timing of pesticide treatments.Up to date, only the white sticky trap exists to estimate sawflies' population density in plum orchards.Neither pheromones nor feeding attractants have been identified to attract any sawfly species, which could help to monitor them.
The number of caught H. minuta, H. flava and H. fulvicornis adults in traps considerably varied between years and locations.For instance, at Erd location comparing two consecutive years the highest average trap catches varied between 146 and 80 in the case of H. minuta males.This could be due to the previous years' insecticide treatment, seasonal differences between years, prolonged diapause of the larvae, or larval survival rate.Tamo si unas et al. ( 2014) also reported different population densities of H. minuta between consecutive years in the same location.
Surprisingly, the traps caught H. fulvicornis for the first time in plum orchards in Hungary.Although the average number of adults caught was low, however, the existence of this species in plum orchards is remarkable.H. minuta and H. fulvicornis are closely related species (Liston et al., 2019), the identification of these species is difficult, therefore, it might be that in earlier studies attention did not focus on the separation of these two species.The catches of H. fulvicornis in the traps do not automatically mean that this species can cause damage to plum fruits.The larvae of this species could develop in other Prunus species' fruits and the adults could fly into the plum orchards, attracted by the white color.Pschorn-Walcher and Altenhofer (2000) show that P. spinosa is the main larval host of this species; although, this assumption was based on the adult occurrence not the larvae in the fruits.In Italy, Roberti (1948) convincingly showed that this species attacks cultivated plum varieties (P.domestica and Prunus salicina).Our study did not focus on the different species' larval development in plum fruits; however, there is a high probability that this species could also damage plum fruits.
Comparing three consecutive years, the first adults were caught in 2014 on the first day of April, in 2015 at Pom az, in the second week of April (April 10), at Erd on the last week of March and 2016 also in the last week of March.Paja c Zivkovi c et al. ( 2020) reported that the first H. minuta and H. flava adults flew at end of March in Croatia, Zagreb in 2019.However, in Lithuania, the white sticky traps caught the first H. minuta and H. flava adults one month later presumably due to the lower annual temperatures between 2010-2012(Tamo si unas et al., 2014)).In terms of the first adult catch in the same year (Pom az 2015, Fig. 2; Erd 2015, Fig. 3), we found 10 days differences between the locations.This could be due to the below-ground temperature differences before the first adult emergence between the locations.In the case of Hoplocampa testudinea, Zijp and Blommers (1997) found a correlation between the soil temperature and first adult emergence.
The average trap catches varied between different locations in the same year.For instance, in 2015 at Erd, on average, traps caught 6 times more H.minuta males as compared to Pom az at the date of the highest trap catch.Most probably, this variability is caused by biological or environmental factors.Prolonged diapause could also be the reason for this phenomenon, which has been observed in H. minuta and H. testudinea populations (Tauber and Tauber, 1976;Hadzistevic, 1959;Leski, 1960).Presumably, the overwintering larval survival rate was higher at Erd compared to Pom az, due to some biotic (parasitoids or fungal diseases) or abiotic factors (climate).For example, entomophagous fungi could cause larval mortality, which has already been reported on H. testudinea (Niezborala, 1978;Jaworska, 1992).
In our study, males were dominant in all locations and years.Conversely, in Lithuania, Tamo si unas et al. (2014) reported that more females than males of H. minuta flew into the traps.Also, in the same study, they show that the ratio of males and females of H. flava was equal.
In terms of species abundance, we found that in almost all locations and years H. minuta was the dominant species, except in 2014 at Cegl ed, where more H.flava than other species flew into the traps.However Paja c Zivkovi c et al. (2020) showed that in Croatia H. flava was more abundant than H. minuta.
The data of trap catch could be used to predict the damage level caused by these species and could help in the timing of the applied insecticides.Further studies should focus on investigating the development of H. fulvicornis larvae in plum fruits and the correlation of blooming time and trap catches of all species in Hungary.Also, future studies could focus on pheromone and feeding attractant identification of these three Hoplocampa species.

Fig. 1 .
Fig. 1.Mean trap captures of H. minuta (A) and H. flava (B) at the inspection dates during the experiment in 2014 at Cegl ed.Error bars represent the standard error of the mean.The pie chart shows the ratio of caught species and the sex ratio of each species (C)