Efficacy of Insecticides against the Tortoise Beetle, Cassida vittata Vill (Coleoptera: Chrysomelidae) and the side effects on Predators in Sugar Beet Fields

Sugar beet, Beta vulgaris L. (Chenopodiaceae) is an industrial economic, and a main source of Egypt’s sugar supply (El-Fergani, 2019). This crop is attacked by many insect pests, one of which is the tortoise beetle, Cassida. vittata Vill.(Coleoptera: Chrysomelidae), which has become a notorious pest of sugar beet in Egypt (Saleh et al., 2009).

Both tortoise beetle larvae and adults feed on the lower side of the sugar beet leaves, where they feed on the lower epidermis and inner tissues, but the upper epidermis remain intact looking like a glass. In addition, adults feed on leaf tissues, causing regular circular holes (Abo El-Ftooh, 1995). Crop loss occurs due to the leaf-feeding behavior which causes a reduction in the sugar content of the infested plants (Aly et al. 1993).

Profenofos and carbosulfan are efficient compounds against all stages of the tortoise beetle (AL-Habashy 2013 and El-khouly and Omar 2002). However, chlorfenapyr demonstrated a moderate toxic effect against the insect.Unfortunately, Shaheen et al. (2011) reported that profenofos, carbosulfan and chlortenapyr showed toxic effects to the predator, Coccinella undecimpunctata. Anter et al. 2020 tested the effect of three pesticides; Selecron (profenofos), Marshal (carbosulfan) and Radiant (spinetoram) against larvae and adults of the tortoise beetle, Cassida vittata (Vill.) inhabiting sugar beet plants. Selecron and Marshal were highly effective against larvae and adults of the pest. However, Radiant (spinetoram) demonstrated a moderate toxic effect. The adult stage of C. undecimpunctata, has been observed in considerable numbers and for a long time in sugar beet field (Askar 2016). (El-Khayat et al., 2012 and Sadanandane et. al., 2012). Reported that, The use of insecticides, caused severe harm to the natural balance between pests and their enemies.

The current work has been carried out for the evaluation of insecticides against C. vittata infesting sugar beet plants and their side effects on some predators in sugar beet fields, at Kafr El-Sheikh Governorate, Egypt, during two consecutive planting seasons, 2020/ 2021 and 2021/ 2022.

MATERIAL AND METHODS     

1. Sugar beet sowing

This experiment was conducted at El-Hamedia village, Kafr El-Sheikh Governorat, with the Gloria sugar beet variety as susceptible to the tortoise beetle, Cassida vittata Vill. An area of about 500 m² was divided into 12 plots, arranged in complete randomized block design, with three replicates Each plot measured 42 m². seeds of Gloria variety were sown on October 15th and 17th in 2020/ 2021 and 2021/ 2022 seasons, respectively. All agricultural practices were followed with the exception of pesticides, rather than the insecticides tested.

2. Tested Insecticides

The field recommended rates of the following insecticides were used against C. vittata using a commercial formulation of each.

- Spinetoram (Radiant 12% SC) (100 cm3/ fed), Daw Agro Sciences Co.

- Acetamiprid 22.7% + Biferthrin 27.3% (Rubek extra WP 5%) (25g /1oo

L water), Shoura Chemical Co.       

- Carbosulfan (Marshal 20 % Ec) (250 cm3 / fed). Delta Chemical Co.

3. Insecticide applications

The three insecticide treatments were performed on April 9th (about six months after sugar beet sowing ), and the check plots were sprayed with only water. Knapsack sprayes (20 L volume) was used.

4. Evaluation of insecticide efficiency

From each plot, ten sugar beet plants were selected randomly one, seven, and ten days after Rubek and Marshal application. The numbers of larvae of C. vittata were counted in the 10 sugar beet plants. In addition, numbers of Coccinella undecimpunctata, Paederus alferii and spiders were recorded on ten plants. Numbers of both tortoise beetle and its associated predators were counted just before treatments, and as abovementioned days after treatments.  

5. Statistical analysis

The percentage reduction in the C. vittata larvae population, as well as the associated predators for all treatments in the two growing seasons, were calculated using Henderson and Tilton’s formula (1955) as follows:

Reduction (%)=

.

RESULTS AND DISCUSSION     

1. 1.     Insecticide efficiency

1.1.    Against C. vittata Larvae

Data in Tables (1 and 2) present the reduction percentage of C. Vittata larvae population in sugar beet fields after treatment with the tested insecticides. In both seasons, spinetoram was effective against the insect population in sugar beet fields. It was noticed that spinetoram was effective against the C. Vittata larvae population three days post-treatment compared to untreated areas, causing 86.62 and 87.32% reductions in larval populations in 2020/2021 and 2021/ 2022 seasons, respectively, compared to the untreated sugar beet plants. However, the highest larval reductions 95.49 and 96.16% in the first and second seasons, after 10 dayes respectively. The initial larval killing ( one day post – treatment) values due to acetamiprid + biferthrin treatment were 91.13 and 92.87% in the first and second seasons, respectively, and reached 98.55 and 98.87% reductions , in the first and second seasons, after 10 dayes respectively, compared to the check ( untreated). High reduction percentages were assessed ten days post-treatment (98.55 and 99.78). Concerning the overall means of reductions in C. Vittata larvae, as presented in Tables (1&2). These reductions averaged 91.04, 95.44 and 95.01% due to spinetoram, acetamiprid + biferthrin and carbosulfan, respectively in 2020/2021season. The corresponding values in 2021/2022 season, were 91.23, 96.01 and 96.93%.

 Thus, it could be reported that the three compounds performed well (achieving more than 90% larval reduction) against C. Vittata.

1.2.    Against Coccinella undecimpunctata

The efficacies of tested insecticides against larvae and adults of C. undecimpunctata are presented in Table (3&4).

In both seasons, the bioinsecticide, spinetoram was safer against the predator, C. undecimpunctata compared to the two other insecticides. The overall means of predator reduction were 28.83, 99.24 and 99.19% due to the applications of spinetoram, acetamiprid + biferthrin and carbosulfan, respectively in the first season (Table 3). The corresponding reduction values in the second season (Table 4) were 28.03. 99.13 and 97.15%. Thus, spinetoram was less toxic to the coccinellid compared to the evaluated conventional insecticides.

Table (1): Reduction percentage of Cassida  vittata larvae in sugar beet fields due to insecticide applications, 2020/ 2021 season

    NR: No recorded data

Table (2): Reduction percentage of Cassida  vittata larvae in sugar beet fields due to insecticide applications, , 2021/ 2022 season

     NR: No recorded data

Table (3): Side effect of insecticides on Coccinella undecimpunctata L. (adults & larvae) at sugar beet fields, , 2020/ 2021 season

    NR: No recorded data

Table (4): Side effect of insecticides on Coccinella undecimpunctata L. (adults & larvae) at sugar beet fields, , 2021/ 2022  season

    NR: No recorded data

1.3. Against Paederus alfierii

Data presented in Tables (5&6) exhibit the side effects of insecticides, applied against C. vittata in sugar beet fields, on the population densities of the insect predator, Paederus alfierii adults.

In the first season (2020/2021), both acetamiprid + biferthrin and carbosulfan sharply reduced the populations of P. alfierii. The initial killing of acetamiprid + biferthrin against the predator was very high (90.51% reduction), followed by that at seven days post- treatment (83.17% reduction) and then by that at ten days post-treatment (80.26% reduction). As for carbosulfan, the P. alfierii population reductions were 36.36, 88.38 and 87.02% at one, seven and ten days post-treatments respectively.

Concerning the side effect of the bioinsecticide, spinetoram, the reductions in P. alfierii populations were 41.56, 43.69 and 49.87% three, seven and ten days after treatments, respectively.

However, the overall means of predator reduction due to spinetoram was 45.04% compared to 84.65% due to acetamiprid + biferthrin and 70.59% due to carbosulfan.

In the second season (2021/2022) (Table 4) adeverse effects of evaluated insecticides against P. alfierii adults were higher than those of the first season. Initial killings of acetamiprid + biferthrin and carbosulfan were very high; 95.48 and 100% reductions, respectively. The residual effects of both insecticides were 93.11 and 92.73% insect predator reductions, respectively.

The bioinsecticide, spinetoram was obviously safer against P. alfierii adults throughout the experimental period. The overall means of insect predator reductions were 41.79, 93.26 and 93.44% for spinetoram, acetamiprid + biferthrin and carbosulfan, respectively.

It could be concluded that spinetoram could be applied against C. vittata infestation in sugar beet fields, particularly when the tortoise beetle populations are moderate, not too heavy. This strategy keeps, to a great extent the populations of the beneficial predator, P. alfierii high.

1.4. Against spiders

In 2020/2021 sugar beet season (Table 7), the overall mean reduction in spider population due to the application of insecticides showed that bioinsecticide, spinetoram was the safest against the spiders. The overall reduction due to this formulation was 35.59%, while acetamiprid + biferthrin and carbosulfan reduced the spider populations by 83.51 and 86.75%, respectively.

Data of the second season (2021/ 2022) were similar to those of the first one, as Also, the bioinsecticide was the safest. ( 36.82% spider population reduction) compared to 92.13 and 89.15% reductions in case of acetamiprid + biferthrin and carbosulfan, respectively.

The obtained results are in line with those of El-Khouly and omar (2002) Shaheen et al (2011) and Al-Habashi (2013) who found that carbosulfan was, in most cases, highly effective against the tortoise beetle, C. vittat. Also, El-Fergani et al (2022) reported the high toxicity of the organophosphorous insecticide, chlorpyrifos against most of sugar beet insect pests, but unfortunately, was highly toxic to most natural enemies, particularly Coccinella undecimpunctata. The low mortality of the bioinsecticide, spinetoram, in the current investigation was also found by shaheen et al (2011) for the same compound, and by Anter et al (2020) for another formulation (Radiant) of the bioinsecticide.

CONCLUSION

From the results of the current investigation, both conventional insecticides were effective against C. vittata, butin the same time, they had adverse side effects on natural enemies, dominant in sugar beet fields. However, in case of moderate population densities ofharmful insects in sugar beet fields, it could be recommended to use the bioinsecticide, spinetoram, which achieves a moderate insect control, but at the same time is safer against natural enemies.

Table (5): Side effect of different insecticides on Paederus alfierii Koch adults  at sugar beet fields, 2020/ 2021 season

     NR: No recorded data

Table (6): Side effect of different insecticides on Paederus alfierii Kochadults  at sugar beet fields, 2021/ 2022 season

    NR: No recorded data

    Table (7): Side effect of different insecticides on spidersat sugar beet fields, 2020/ 2021season

    NR: No recorded data

Table (8): Side effect of different insecticides onspidersat sugar beet fields , 2021/ 2022 season