Soybean seed damage by different species of stink bugs

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1 Agricultural and Forest Entomology (2002) 4, 145±150 Soybean seed damage by different species of stink bugs Beatriz S. CorreÃa-Ferreira and Joacir de Azevedo Embrapa Soja, Caixa Postal 231, CEP , Londrina, PR, Brazil Abstract 1 Damage caused by the three main species of stink bugs occurring on soybean Nezara viridula (Linnaeus), Piezodorus guildinii (Westwood) and Euschistus heros (Fabricius) was compared in field cages and in greenhouses. Infestation levels of 4 stink bugs=m row of plants (field cages) and 2 stink bug=plant (greenhouse) for 15 days during the pod filling stage are reported. At harvest, the yield and seed quality were evaluated. 2 In the field, there was no difference in yield between infested and insect-free plants, but damage to seed quality varied with stink bug species. Plants damaged by P. guildinii had the lowest quality seeds. From 50 g seed samples harvested in the field, the mean weight of seeds classified as `good' was 37.3 g in plants infested with P. guildinii, compared to 41.8, 44.2 and 46.6 g in plants infested with E. heros, N. viridula and the control, respectively. 3 Plants infested with P. guildinii showed the highest number of seeds damaged by stink bugs, whereas those infested with E. heros showed the lowest damage. 4 Plants infested with P. guildinii had 18.5% damaged seeds, higher than the 3.6% and 3.4% damaged seeds from plants infested with the two other species and 0.1% in control plants. The percentage of non-viable seeds due to stink bug damage was 5.7% for P. guildinii but lower for the other two species. Keywords Euschistus heros, Glycine max, Nezara viridula, Pentatomidae, Piezodorus guildinii, seed quality, stink bug damage, yield. Introduction Stink bugs, especially those of the Pentatomidae family, are considered to be one of the most important pests in soybean producing areas in various parts of the world (Turnipseed & Kogan, 1976; Vicentini & Jimenez, 1977; Panizzi & Slansky, 1985). At least 54 stink bug species have been recorded in soybean areas (Panizzi & Slansky, 1985), but few are harmful to the crop. Of the complex of 25 stink bug species found in soybean in Brazil, three are economically important, Euschistus heros (Fabricius), Nezara viridula (Linnaeus) and Piezodorus guildinii (Westwood) (Panizzi & Slansky, 1985). The neotropical brown stink bug E. heros is currently the most abundant species, especially in the central region of Brazil, at latitudes between 0 and 23 (Panizzi & Correà a- Ferreira, 1997). Several studies have been published on the impact of stink bug feeding, which can cause significant losses in soybean yield, quality and germination potential (Miner, Correspondence: Beatriz S. Correà a-ferreira. Tel.: ; fax: ; beatriz@cnpso.embrapa.br 1961; Daugherty et al., 1964; Jensen & Newsom, 1972; Todd & Turnipseed, 1974; Vicentini & Jimenez, 1977; McPherson et al., 1979; Panizzi et al., 1979; Brier, 1993). In addition, plants attacked by stink bugs can have seeds with low vigour, lower oil content and greater protein content. Stink bugs are also associated with the transmission of the fungus Nematospora coryli Peglion, and other diseases (Kilpatrick & Hartwig, 1955; Daugherty, 1967; Clarke & Wilde, 1971; Corso & Heinrichs, 1974; Thomas et al., 1974; Vicentini & Jimenez, 1977; Galileo & Heinrichs, 1978a; Panizzi et al., 1979; Villas-Boà as et al., 1990). One of the causes of leaf retention in soybean is attributed to stink bug attack (Daugherty et al., 1964; Corso & Heinrichs, 1974), although several other factors can contribute to the occurrence of this phenomenon (Hicks & Pendleton, 1969; Mascarenhas et al., 1987). Sosa-Go mez & Moscardi (1995), investigating the leaf retention potential of the different stink bug species by artificial infestation in soybean, found that P. guildinii caused greater leaf retention than N. viridula, whereas plants infested with E. heros showed practically no leaf retention. # 2002 The Royal Entomological Society

2 146 B. S. CorreÃa-Ferreira and J. de Azevedo Comparative studies have been carried out by several authors in different growing areas due to the diversity of stink bug species present in soybean. In Australia, N. viridula, Piezodorus hybneri (Gmelin) Dictyotus caenosus (Westwood) and Plautia affinis Dallas make up the Pentatomidae complex in soybean and damage caused by the different species varies greatly (Brier, 1993). His study showed that N. viridula damages more seeds than other species, and this damage is three times more severe than caused by P. hybneri. Miner (1961), comparing damage caused to soybean by Acrosternum hilare (Say), N. viridula and Euschistus servus (Say), found that the type and severity of the damage caused by the first species were identical to that found for N. viridula, but that less damage ensued when the plants were infested by E. servus. McPherson et al. (1979) obtained similar results, except for E. servus last-stage nymphs and adults, which caused damage in soybean comparable to that resulting from N. viridula and A. hilare. In Argentina, field tests indicated that P. guildinii is the stink bug with the greatest capacity to cause damage to soybean, although it is not considered to be responsible for the greatest losses as it is not the most abundant species in the area (Vicentini & Jimenez, 1977). Costa & Corseuil (1979) and Galileo & Heinrichs (1978a,b) working with the same species of stink bug in Brazil obtained significant reductions in yield when P. guildinii attacked plants throughout the pod development-filling period. Later, Panizzi et al. (1979) showed that within this same critical period the most susceptible growth stages of the plant to the attack by P. guildinii, occur in the mid period of pod development and continue to a week before pod-filling completion. The intensity of the damage caused by stink bugs is directly related to their population level and to the plant development stage. There are several studies that assess the damage caused by different stink bug population levels compared to the different soybean development stages (Panizzi et al., 1979; Schumann & Todd, 1982; McPherson et al., 1993; McPherson, 1996). The results show that although stink bugs begin soybean field colonization at the end of the vegetative phase or during flowering, their populations increase from pod development reaching the highest population densities at the end of pod filling. Pod development to pod filling is therefore the most critical period for insect attack (Correà a-ferreira & Panizzi, 1999). In integrated pest management systems, control decisions are currently based on the level of economic damage, which depends on the stink bug population in the crop and the development stage of soybean. This study aimed to compare the damage caused by the three main stink bug species that occur in soybean during the critical periods, taking into account the diversity of stink bugs found in soybean and their predominance in different regions of Brazil. soybean by the stink bug species N. viridula, P. guildinii and E. heros. Field experiment `BR 37' soybean (medium maturity variety, with cycle of 135 days) were planted in November, within the ideal planting time for soybean production in northern Parana and within 0.45 m row spacing. Soybean plants were infested with adult N. viridula, P. guildinii and E. heros stink bugs at a level of four stink bugs=m row of plants (8 per cage) for 15 days during the pod-filling period (R5±R6) (Fehr & Caviness, 1977), using screen field cages (1 m 1m 1 m), randomly distributed but with a minimum of 4.5 m spacing. The plants were inspected every 2 days and dead stink bugs were replaced. After the infestation period, the insects were eliminated from the cages by applying endosulfan (350 g a.i.=ha) by a costal sprayer. Control cages were kept free from stink bug attack throughout the crop cycle by weekly insecticide application. Yield was assessed at harvest, with seed weight standardized to 13% humidity. Seed quality of control plants and of those infested with the different stink bug species was evaluated by visual examination of 50 g samples, with seeds being classified into three categories: good seeds (seeds without apparent stink bug damage, with normal colour and shape), medium (seeds with some damage) and bad (totally damaged seeds, wrinkled and deformed); and by the tetrazolium test (TZ), classifying the seeds in the 1±8 categories (percentage of sucked seeds) and 6±8 (percentage of non-viable seeds due to stink bug damage) (FrancË a Neto et al., 1998). Greenhouse experiment Soybean plants, Parana cultivar (early maturity variety, with cycle of 110 days) grown in pots and covered with net screening, were infested with adult N. viridula, P. guildinii and E. heros at a level of 2 stink bugs=plant for 15 days during the pod-filling period (R5±R6). During the infestation period, the plants were inspected, and dead stink bugs replaced. After the infestation period, the stink bugs were removed and the plants kept until maturity under the same greenhouse conditions. At harvest, the mean soybean grain yield, the number of good and empty pods per plant, and the seed quality of the control plants and those infested with the different stink bug species were assessed by visual analysis and the tetrazolium test, as described for the field experiment. A completely randomized design was used with four treatments and seven replications in the field experiment and eight replications in the greenhouse experiment. Analysis of variance was performed and the means compared by the Tukey test at 5% level of probability. Methods Field and greenhouse experiments were set up at Warta District, in Londrina county, northern ParanaÂ, Brazil, in the 1997±1998 season to compare the damage caused to Results and discussion Field experiment Soybean plants infested with 4 stink bugs=m for 15 days during the pod-filling period showed no significant

3 Soybean damage by stink bugs 147 reduction in yield when compared with insect-free plants (F ˆ 0.89; d.f. ˆ 3,24; P ˆ 0.46). Mean field yields varied from kg=ha in the control plants to kg=ha in plants infested with adult N. viridula (Table 1). These results are in line with those obtained by Panizzi et al. (1979) when infestations of four P. guildinii=m for 25 days were used during the pod-filling period (R5±R6), although these authors also found significantly lower yields when the plants were infested with these stink bugs for 49 days. This finding was also supported by studies by Villas-Boà as et al. (1990) and Gazzoni (1998) who, working with natural infestations, did not record reduced soybean yields at levels of up to 4 stink bugs=m (Table 1). The soybean pod-filling period is critical for stink bug attack (Duncan & Walker, 1968; Panizzi et al., 1979; Brier & Rogers, 1991) and the minimal effect of these insects on the soybean yield may be explained by the exposure time (15 days) and the population level used (4 stink bugs=m) in this experiment. Studies in the literature report reductions in soybean yield especially for longer infestation times than the one used here (more than 21 days) or greater stink bug population densities (Thomas et al., 1974; Todd & Turnipseed, 1974; Vicentini & Jimenez, 1977; Yeargan, 1977; Galileo & Heinrichs, 1978b; McPherson et al., 1979; Panizzi et al., 1979). Significant differences in seed quality were recorded following infestation by different stink bug species in this study, all resulting in plants with significantly inferior seed quality when compared to the controls (Table 2). The results from the visual assessments and from the tetrazolium test showed that soybean plants damaged by P. guildinii had most poor quality seeds. The weight of seeds classified as of medium quality also varied with the different stink bug species, but it was in the weight of completely damaged seeds (bad quality seeds) that the most serious effect of P. guildinii was recorded. The results from the tetrazolium test indicated an increase in the percentage of sucked (complete damage) and nonviable seeds, when the soybean plants were infested with P. guildinii compared with the other stink bug species. Plants with P. guildinii, after 15 days infestation of 4 stink bugs=m, had 18.5% of their seeds punctured by the insect, significantly greater than the values found in the plants with E. heros, N. viridula and control (F ˆ ; d.f. ˆ 3,23; P < 0.001; Table 2). The findings for the percentage of non-viable seeds following stink bug infestation (TZ 6±8) showed a similar trend (F ˆ 61.54; d.f. ˆ 3,23; P < 0.001). In the field, no statistical differences were found in soybean seed quality between plants infested with N. viridula and E. heros, although there was a tendency to less damage in the plants with the neotropical brown stink bug. Similar trends were found by Sosa-Go mez & Moscardi (1995) when the capacity of these species to cause leaf retention in soybean was assessed. Table 1 Yields of soybean seeds from plants infested by different stink bug species (4 stink bugs=m) for 15 days, during pod filling stage (R5±R6), in field cages Stink bug species Yield (kg=ha) 1 X( SEM) Control NS Euschistus heros Nezara viridula Piezodorus guildinii NS ˆ non significant by Tukey test 5%. Greenhouse experiment The mean yield of the control plants and those infested with two stink bugs per plant for 15 days varied from 10.9 g in the control to 4.6 g in the plants infested with adult P. guildinii (Table 3). No significant differences were found among plants attacked by E. heros or N. viridula and the control, with mean yields of 8.5 g and 6.2 g per plant infested by the two stink bug species, respectively, but a significantly lower yield was recorded in plants infested with P. guidinii (F ˆ 13.61; d.f. ˆ 3,28; P < 0.001). Table 2 Quality of soybean seed from plants infested by different stink bug species (4 stink bugs=m) for 15 days, during pod filling stage (R5±R6), in field cages Mean seed weight (g) 1,2,3 Tetrazolium test (%) 1,2 Treatments Good Medium Bad (1±8) 4,5 (6±8) 5 Control a c b c b Euschistus heros b ab b b b Nezara viridula ab bc b b b Piezodorus guildinii c a a a a F Value P < < < < < Means followed by the same letter in each column do not differ significantly, Tukey 5%. 2 Means ( SEM) 3 Weight in seed samples of 50 g. 4 Data transformed to arcsine square root (x=100) for analysis. 5 Tetrazolium test: (1±8) ˆ % sucked seeds; (6±8) ˆ % nonviable seeds.

4 148 B. S. CorreÃa-Ferreira and J. de Azevedo Table 3 Yield of soybean plants infested by different stink bug species (2 stink bug=plant), for 15 days during pod filling stage, in a greenhouse Mean number of pods=plant 1,2 Treatments Yield=Plant (g) 1,2 Full 3 Empty Control a a c Euschistus heros a a c Nezara viridula ab ab b Piezodorus guildinii b b a 1 Means followed by the same letter in each column do not differ significantly, Tukey 5%. 2 Means ( SEM) 3 Data transformed to square root (x 0.5) for analysis. The number of full and completely developed pods was similar in the insect-free plants and those infested with adult E. heros and N. viridula. Plants infested with P. guildinii had significantly lower numbers of pods=plant than controls (F ˆ 5.40; d.f. ˆ 3,28; P ˆ ; Table 3). Infestation by P. guildinii also resulted in the largest number of empty pods per plant. Although it is known that the occurrence of underdeveloped pods (empty pods) is not exclusively the result of stink bug damage, in this experiment a clear difference was found between treatments with P. guildinii and the treatments with either E. heros or N. viridula (2.9 and 11.7 empty pods per plant, respectively). Plants infested with E. heros had a similar number of empty pods to the control plants (F ˆ 8.70; d.f. ˆ 3,28; P < 0.001; Table 3). Soybean seed quality was affected by the infestation of the different stink bug species during the pod-filling period. In the control plants, 97.4% of seeds collected had the normal appearance and size of good seeds, corresponding to a weight of 10.7 g seeds, significantly greater than the quantity of good seeds collected from plants infested by the three stink bug species (Table 4). No difference was found among the plants with N. viridula and P. guildinii, but those infested with E. heros had the least damage compared to the control, with 43.6% of the seeds classified as good and without apparent stink bug damage and reaching a weight of 4.5 g. In the plants attacked by N. viridula and by P. guildinii (Table 4), there was a high number of damaged and deformed seeds, with indexes of 58.1% in plants attacked by N. viridula and 73.2% in those infested with P. guildinii, corresponding to a mean number of 45.0 and 47.4 bad seeds=plant. This compares with 0.2 in the plants free from stink bug attack. The greater damage to soybean quality after infestation by P. guildinii was also highlighted by the tetrazolium test. The plants infested with this species had, on average, 18.0% sucked seeds (TZ 1±8) compared to smaller values obtained in the plants infested with E. heros or N. viridula and the control (F ˆ 88.57; d.f. ˆ 3,11; P < 0.001; Table 5). The percentage of non-viable seeds caused by P. guildinii damage (TZ 6±8) (mean value of 6.0%) was statistically different from the other treatments. No difference was found among the plants infested with E. heros and N. viridula for either sucked or non-viable seeds, but in both cases significantly more damage compared to the control plants was recorded (F ˆ 17.01; d.f. ˆ 3,11; P < 0.001) (Table 5). The results obtained showed a damage differential for the three most common stink bug species in soybean in Brazil, especially for effects on seed quality. Piezodorus guildinii was the most damaging species, whereas E. heros, although currently the most abundant species, was the stink bug with the least damage potential to soybean. The smaller effect of stink bugs on the soybean yield can be explained by the capacity of the plant to compensate by increasing the weight of the undamaged seeds, as reported by Russin et al. (1987). This compensation also explains the inconsistent responses in the seed weight to stink bug infestation reported in the literature (Todd & Turnipseed, 1974; Yeargan, 1977). In the United States, the effects of N. viridula, A. hilare and E. servus have been studied and the latter found to be the least damaging species to soybean (Miner, 1961). In Australia, because of the variation in damage caused by Table 4 Quality of soybean seeds from plants infested by different stink bug species (2 stink bugs=plant) for 15 days, during pod filling stage (R5±R6), in a greenhouse Good seeds=plant Bad seeds=plant Treatments N 1,2 Weight (g) 1,2 % N 1,2 Weight (g) 1,2 % Control ,42 a a b b 0.4 Euschistus heros b b b b 19.1 Nezara viridula c c a a 58.1 Piezodorus guildinii c c a a Means followed by the same letter in each column do not differ significantly, Tukey test 5%. 2 Means ( SEM)

5 Soybean damage by stink bugs 149 Table 5 Stink bug damage on soybean seeds from plants infested by different species during 15 days in pod filling, in a greenhouse Treatment different stink bug species, the control decision is dependent on the predominant stink bug species in the region; N. viridula is considered the species that causes greatest damage to soybean (Brier, 1993). In Argentina, studies by Vicentini & Jimenez (1977) also emphasized the potential of P. guildinii as the most aggressive species to soybean. The damage effect of the adult P. guildinii has already been reported by Galileo & Heinrichs (1978a,b) and Panizzi et al. (1979), and more recently by Sosa-Go mez & Moscardi (1995), who assessed the differential capacity to cause leaf retention. The present work reinforces these results, confirming the greater potential of P. guildinii damage to soybean seed quality when compared with N. viridula and E. heros. This difference is possibly associated with the biochemical characteristics of the saliva injected by this species at feeding (Sosa-Go mez & Moscardi, 1995), as well as the presence of toxins, the N. coryli fungus and the P. guildinii feeding behaviour. The accentuated occurrence of neotropical brown stink bug, as the predominant species in soybean crops, particularly in the latitudes below 23 S, and their lesser damage potential indicate, the need for more detailed studies to provide a basis for decisions on suitable control measures, avoiding unnecessary expense and greater risks of environmental contamination. Due the predominance and fluctuation of different species that compose the soybean stink bug complex and its different impacts to the crop, the assessment of damage caused to soybean by these stink bugs is important for the implementation of wide-ranging and efficient integrated pest management systems. Acknowledgements We thank Drs Norman Neumaier and Lenita J. 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