Table 1:
Entomopathogenic nematodes infection (% ± SEM)) on eggs of Helicoverpa zea and Chrysodeixis includens in the laboratory (25°C, 85% RH).
| EPN strain | H. zea | C. includens | |
|---|---|---|---|
| Unfertilized eggsa | Mixed eggs | Mixed eggs | |
| Heterorhabditis bacteriophora (HP88) | 0.0 ± 0.0 a | 5.0 ± 3.4 ab | 6.7 ± 3.3 a |
| Heterorhabditis bacteriophora (VS) | 1.7 ± 1.7 a | 1.7 ± 1.7 ab | 0.0 ± 0.0 a |
| Heterorhabditis floridensis (K22) | 6.7 ± 3.3 a | 10.0 ± 6.3 ab | 0.0 ± 0.0 a |
| Heterorhabditis georgiana (kesha) | 0.0 ± 0.0 a | 11.7 ± 4.0 a | 0.0 ± 0.0 a |
| Steinernema carpocapsae (All) | 1.7 ± 1.7 a | 0.0 ± 0.0 b | 1.7 ± 1.7 a |
| Steinernema carpocapsae (Cxrd) | 1.7 ± 1.7 a | 3.3 ± 1.7 ab | 1.7 ± 1.7 a |
| Steinernema feltiae (SN) | 0.0 ± 0.0 a | 3.3 ± 2.1 ab | 6.7 ± 4.9 a |
| Steinernema rarum (17c+e) | 0.0 ± 0.0 a | 1.7 ± 1.7 ab | 0.0 ± 0.0 a |
| Steinernema riobrave (355) | 1.7 ± 1.7 a | 6.7 ± 2.1 ab | 0.0 ± 0.0 a |
| Steinernema riobrave (7–12) | 1.7 ± 1.7 a | 0.0 ± 0.0 b | 3.3 ± 3.3 a |
| Water | 0.0 ± 0.0 a | 0.0 ± 0.0 b | 0.0 ± 0.0 a |
| F-value (10, 55) | 1.53 | 2.64 | 1.64 |
| P-value | 0.1534 | 0.0104 | 0.1193 |
Mean values within a column followed by the same letter are not significantly different at P > 0.05 (Tukey's HSD test).
Figure 1:
EPN infection on eggs of Helicoverpa zea and Chrysodeixis includens. (A) An infectious juvenile of Steinernema carpocapsae (all strain) was infecting an egg of H. zea with part of its body inside the egg. (B) An infected egg of H. zea by Heterorhabditis georgiana (kesha strain), from which 50 progeny juveniles were produced. (C) A larva of H. zea killed inside an egg by H. floridensis (K22) with young juveniles inside four adult female nematodes. (D) A larva of C. includens killed inside an egg by a juvenile of S. feltiae (SN). (E) A head capsule of a C. includens larva left after a juvenile of S. feltiae (SN) developed inside the egg. (F) A head capsule of a C. includens larva inside an egg with newly emerged juveniles of S. feltiae (SN).
Figure 2:
Larvae of (A) Helicoverpa zea and (B) Chrysodeixis includens inside eggs where larvae biting the eggshells and the protruding hairs of larvae were visible. (C) An adult of Heterorhabditis floridensis (K22 strain) from an H. zea egg with a few juveniles inside its body, and (D) two adults of Steinernema carpocapsae (all strain) from a fifth instar of C. includens with many juveniles inside one adult and eggs inside another.
Table 2:
Mortality (% ± SEM) of first to fourth instars, fifth instars, and pupae of Helicoverpa. zea and Chrysodeixis includens caused by 10 entomopathogenic nematode strains in the laboratory (25°C, 85% RH).
| EPN strains | H. zea | C. includens | H. zea and C. includens | ||||
|---|---|---|---|---|---|---|---|
| First-fourth instars | Fifth instars | Pupae | First-fourth instars | Fifth instars | Pupae | Avg of first-fourthand fifth instarsa | |
| Heterorhabditis bacteriophora (HP88) | 100.0 ± 0.0 a | 81.7 ± 6.0 ab | 6.7 ± 4.9 ab | 80.0 ± 7.3 a | 96.7 ± 2.1 a | 33.3 ± 11.7 abc | 89.6 |
| Heterorhabditis bacteriophora (VS) | 98.3 ± 1.7 a | 81.7 ± 4.8 ab | 15.0 ± 4.3 ab | 72.6 ± 5.4 ab | 93.3 ± 4.9 a | 40.0 ± 11.8 ab | 86.5 |
| Heterorhabditis floridensis (K22) | 98.3 ± 1.7 a | 85.0 ± 7.6 ab | 21.7 ± 8.7 ab | 88.3 ± 3.1 a | 100.0 ± 0.0 a | 30.0 ± 8.9 abc | 92.9 (top 5) |
| Heterorhabditis georgiana (kesha) | 100.0 ± 0.0 a | 83.3 ± 4.2 ab | 13.3 ± 4.2 ab | 90.0 ± 4.5 a | 95.0 ± 3.4 a | 45.0 ± 5.0 ab | 92.0 (top 5) |
| Steinernema carpocapsae (All) | 100.0 ± 0.0 a | 95.0 ± 3.4 a | 20.0 ± 6.8 ab | 85.0 ± 2.2 a | 98.3 ± 1.7 a | 41.7 ± 9.5 ab | 94.6 (top 5) |
| Steinernema carpocapsae (Cxrd) | 100.0 ± 0.0 a | 85.0 ± 8.1 ab | 21.7 ± 6.0 ab | 80.0 ± 8.6 a | 98.3 ± 1.7 a | 36.7 ± 12.3 ab | 90.8 |
| Steinernema feltiae (SN) | 100.0 ± 0.0 a | 76.7 ± 6.7 ab | 5.0 ± 2.2 ab | 40.0 ± 5.8 b | 95.0 ± 3.4 a | 18.3 ± 6.0 bc | 77.9 |
| Steinernema rarum (17c+e) | 100.0 ± 0.0 a | 58.3 ± 13.8 b | 13.3 ± 5.6 ab | 71.7 ± 7.4 ab | 88.3 ± 7.9 a | 26.7 ± 4.9 abc | 79.6 |
| Steinernema riobrave (355) | 100.0 ± 0.0 a | 88.3 ± 5.4 ab | 21.7 ± 6.5 a | 86.7 ± 6.1 a | 100.0 ± 0.0 a | 61.7 ± 7.0 a | 93.8 (top 5) |
| Steinernema riobrave (7–12) | 100.0 ± 0.0 a | 93.3 ± 4.9 a | 15.0 ± 4.3 ab | 90.0 ± 5.2 a | 98.3 ± 1.7 a | 63. 3 ± 4.2 a | 95.4 (top 5) |
| Water | 3.3 ± 3.3 b | 0.0 ± 0.0 c | 0.0 ± 0.0 b | 0.0 ± 0.0 c | 0.0 ± 0.0 b | 1.7 ± 1.7 c | 0 |
| F-Value (10, 55) | 187.99 | 15.81 | 2.42 | 18.4 | 41.62 | 4.99 | |
| P-Value | <.0001 | <.0001 | 0.0184 | <.0001 | <.0001 | <.0001 | |
Figure 3:
EPN infection of larvae and pupae of Helicoverpa zea and Chrysodeixis includens. (A) Adults of Steinernema rarum (17c+e strain) inside a larva of H. zea. (B) Large adults of S. carpocapsae (all) inside the head of C. includens larva. (C) Juveniles of S. riobrave (7–12) from a pupa of H. zea in a White trap. (D) Adults of Heterorhabditis georgiana (kesha strain) inside a pupa of Chrysodeixis includens.
Figure 4:
EPN suspension with and without an adjuvant. (A) Without an adjuvant, suspension was distributed unevenly on a corn leaf; air bubbles were visible. (B) With SAg Surfactant, suspension was distributed evenly across the corn leaf, which may help nematodes to find hosts and hide in pores on a corn leaf. (C) Without an adjuvant, many EPNs were trapped in water droplets, including on the leaf and insect. (D) With SAg Surfactant, a juvenile was able to search and move around more freely, allowing it to attempt to hide in a small leaf gap when the leaf was getting dry.
Table 3:
Effect of Steinernema carpocapsae (all strain) with an adjuvant on first instars of Helicoverpa zea in corn plants in a corn field (2022, Leland, Mississippi).
| Field exp., # Experiment date Temperature RH Weather condition | EPN Rate Plant Age Plant high | Treatment | # of Insects | % Mortality ± SEM | % EPN Infection ± SEM |
|---|---|---|---|---|---|
| Field exp, #1 | 20 IJs/cm2 | S. carpocapsae (All) + SAg^ | 63 | 78.2 ± 9.2 a | 35.0 ± 10.3 a |
| June 17, 2022 | |||||
| 24(23–35) °Ca | 6 wk | S. carpocapsae (All) | 56 | 69.3 ± 7.8 a | 24.2 ± 10.2 a |
| 82(62–99) %RH | 1.1 m | Water + SAg | 64 | 22.0 ± 4.6 b | 0.0 ± 0.0 b |
| 30 min heavy rain | Water | 53 | 28.0 ± 8.1 b | 0.0 ± 0.0 b | |
| F(3, 12)=20.66 | F(3, 12)=10.95 | ||||
| P < 0.0001 | P < 0.0009 | ||||
| Field exp., #2 | 40 IJs/cm2 | S. carpocapsae (All) + SAg | 80 | 87.7 ± 1.1 a | 66.4 ± 4.7 a |
| June 27, 2022 | |||||
| 22(19–30) °C | 7.5 wk | S. carpocapsae (All) | 58 | 70.4 ± 3.6 b | 42.0 ± 2.5 b |
| 83(58–94) %RH | 1.3 m | Water + SAg | 65 | 18.7 ± 4.5 c | 0.0 ± 0.0 c |
| Partly Cloudy | Water | 74 | 21.6 ± 3.1 c | 0.0 ± 0.0 c | |
| F(3, 12)=77.26 | F(3, 12)=294.09 | ||||
| P < 0.0001 | P < 0.0001) |
Mean values within a column followed by the same letter are not significantly different at P > 0.05 (Tukey's HSD test).
a Numbers outside parentheses were the temperature or RH at the beginning of spaying, numbers inside parentheses were the lowest-highest temperature or RH during 24 hr.
^SAg= 0.066% SAg Surfactant.
Table 4:
Effect of Steinernema riobrave (7–12 strain) and Steinernema carpocapsae (all strain) with an adjuvant on fifth instars of Chrysodeixis includens on soybean plants in soybean fields (2022, Leland, Mississippi).
| Experiment date Temperature RH Weather condition | EPN rate Plant age Plant high | Treatment | # of Insects | % Mortality ± SEM | % EPN Infection ± SEM |
|---|---|---|---|---|---|
| Field exp., #1 August 3, 2022 | 40 IJs/cm2 | S. carpocapsae (All) + SAg^ | 37 | 92.9 ± 4.7 a | 37.1 ± 7.6 a |
| 24(22–35) °Ca | 9 wk | S. riobrave (7–12) + SAg | 51 | 25.2 ± 12.6 b | 0.0 ± 0.0 b |
| 88(60–97) %RH | 0.5 m | Water + SAg | 38 | 13.0 ± 7.2 b | 0.0 ± 0.0 b |
| Most sunny | F(2, 9)=16.82 | F(2, 9)=58.4 | |||
| P=0.0009 | P < 0.0001 | ||||
| Field exp., #2 September 8, 2022 | 10 IJs/cm2 | S. carpocapsae (All) + SAg | 95 | 23.7 ± 4.8 a | 7.1 ± 1.4 a |
| 22(19–32) °C | 8 wk | S. riobrave (7–12) + SAg | 91 | 6.2 ± 1.3 b | 0.0 ± 0.0 b |
| 79(40–95) %RH | 0.4 m | Water + SAg | 84 | 1.09 ± 1.1 b | 0.0 ± 0.0 b |
| Sunny | F(2, 9)=21.28 | F(2, 9)=73.04 | |||
| P=0.0004 | P < 0.0001 |
Mean values within a column followed by the same letter are not significantly different at P > 0.05 (Tukey's HSD test).
a Numbers outside parentheses were the temperature or RH at the beginning of spaying, numbers inside parentheses were the lowest-highest temperature or RH during 24 hr.
^SAg= 0.066% SAg Surfactant.