P. Glynn Tillman

Comparison of Susceptibility of Pest Euschistus servus and Predator Podisus maculiventris (Heteroptera: Pentatomidae) to Selected Insecticides

Abstract Susceptibility of the brown stink bug, Euschistus servus (Say), and the spined soldier bug, Podisus maculiventris (Say), to acetamiprid, cyfluthrin, dicrotophos, indoxacarb, oxamyl, and thiamethoxam, was compared in residual and oral toxicity tests. Generally, susceptibility of P. maculiventris to insecticides was significantly greater than or not significantly different from that of E. servus. Cyfluthrin and oxamyl were more toxic to the predator than to E. servus in residual and feeding tests, respectively. Dicrotophos is the only compound that exhibited both good residual and oral activity against E. servus, but even this toxicant was more toxic to the predator than to the pest in oral toxicity tests. Feeding on indoxacarb-treated food caused high mortality for both nymphs and adults of P. maculiventris. In contrast, E. servus was unaffected by feeding on food treated with this compound. Insecticide selectivity to P. maculiventris was detected only with acetamiprid for adults in residual toxicity tests and for nymphs in oral toxicity tests. Because insecticide selectivity to P. maculiventris was limited, it is extremely important to conserve P. maculiventris in cotton fields by applying these insecticides for control of brown stink bugs only when the pest reaches economic threshold.

Composition and Abundance of Stink Bugs (Heteroptera: Pentatomidae) in Corn

ABSTRACT The species composition and abundance of stink bugs (Heteroptera: Pentatomidae) in corn, Zea mays L., was determined in this on-farm study in Georgia. Seven species of phytophagous stink bugs were found on corn with the predominant species being Nezara viridula (L.) and Euschistus servus (Say). All developmental stages of these two pests were found, indicating they were developing on the corn crop. The remaining five species, Oebalus pugnax pugnax (F.), Euschistus quadrator (Rolston), Euschistus tristigmus (Say), Euschistus ictericus (L.), and Acrosternum hilare (Say), were found in relatively low numbers. Adult N. viridula were parasitized by the tachinid parasitoid Trichopoda pennipes (F.). There was a pronounced edge effect in distribution of stink bugs in corn. Population dynamics of N. viridula and E. servus were different on early and late-planted corn. Oviposition by females of both stink bug species occurred in mid-to-late-May and again mid-to-late-June in corn, regardless of planting date. In early planted fields, if stink bug females oviposited on corn in mid-July, the resulting nymphs did not survive to the adult stage in corn because ears were close to physiological maturity and leaves were senescing. Density of stink bug adults in early planted corn was relatively low throughout the growing season. In late-planted corn, females of both stink bug species consistently laid eggs in mid-to-late-July on corn with developing ears. This habitat favored continued nymph development, and the resulting adult population reached high levels. These results indicate that corn management practices play a key role in the ecology of stink bugs in corn agroecosystems and provide information for designing management strategies to suppress stink bugs in farmscapes with corn.

Impact of Brown Stink Bug (Heteroptera: Pentatomidae) Feeding on Corn Grain Yield Components and Quality

ABSTRACT Brown stink bug, Euschistus servus (Say) (Heteroptera: Pentatomidae), damage on developing corn, Zea mays L., ears was examined in 2005 and 2006 by using eight parameters related to its yield and kernel quality. Stink bug infestations were initiated when the corn plants were at tasseling (VT), mid-silking (R1), and blister (R2) stages by using zero, three, and six in 2005 or zero, one, two, and four bugs per ear in 2006, and maintained for 9 d. The percentage of discolored kernels was affected by stink bug number in both years, but not always affected by plant growth stage. The growth stage effect on the percentage of discolored kernels was significant in 2006, but not in 2005. The percentage of aborted kernels was affected by both stink bug number and plant growth stage in 2005 but not in 2006. Kernel weight was significantly reduced when three E. servus adults were confined on a corn ear at stage VT or R1 for 9 d in 2005, whereas one or two adults per ear resulted in no kernel weight loss, but four E. servus adults did cause significant kernel weight loss at stage VT in 2006. Stink bug feeding injury at stage R2 did not affect kernel damage, ear weight or grain weight in either year. The infestation duration (9 or 18 d) was positively correlated to the percentage of discolored kernels but did not affect kernel or ear weight. Based on the regression equations between the kernel weight and stink bug number, the gain threshold or economic injury level should be 0.5 bugs per ear for 9 d at stage VT and less for stage R1. This information will be useful in developing management guidelines for stink bugs in field corn during ear formation and early grain filling stages.

Transmission of Ascovirus from Heliothis virescens (Lepidoptera: Noctuidae) by Three Parasitoids and Effects of Virus on Survival of Parasitoid Cardiochiles nigriceps (Hymenoptera: Braconidae)

Abstract In field crops in the southeastern United States, larvae of Heliothis virescens (F.) are often infected with ascoviruses, especially toward the end of the growing season. Ascoviruses are unusual in that they are difficult to transmit per os, and several studies have provided data indicating that these viruses are vectored mechanically by parasitic wasps during oviposition. In Georgia, three parasitoids commonly parasitize H. virescens larvae: Cardiochiles nigriceps Viereck, Campoletis sonorensis (Cameron), and Microplitis croceipes (Cresson). In the current study, we investigated the transmission of ascovirus by these parasitoids by using females that were collected in the field or reared in the laboratory. After a single oviposition by C. nigriceps in an H. virescens larva with a 4-d-old ascovirus infection, all subsequent healthy larvae parasitized by this female developed ascovirus infection. After oviposition in an infected larva, examination of C. nigriceps by using transmission electron microscopy showed that ascovirus virions and ascovirus vesicles adhered to the inner surface of the ovipositor. The ovipositor of M. croceipes was shorter than those of C. nigriceps or C. sonorensis, and this was correlated with a lower rate of ascovirus transmission by the former species. Observation of C. nigriceps populations in the field indicates this species survives even when ascovirus prevalence in H. virescens is high. Laboratory studies of this host–parasite–virus system showed C. nigriceps larvae survived infection of their host if parasitoid larvae were at least second instars at the time of infection. If an ascovirus infection in the first H. virescens host was no older 48 h, a C. nigriceps female sometimes did not transmit ascovirus to subsequent hosts. Exposure to environmental conditions of the field decreased the capacity of C. nigriceps to transmit ascovirus, and transmission also decreased over the longevity of female parasitoids.

Susceptibility of Pest Nezara viridula (Heteroptera: Pentatomidae) and Parasitoid Trichopoda pennipes (Diptera: Tachinidae) to Selected Insecticides

Susceptibility of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), and its endoparasitoid Trichopoda pennipes (F.) (Diptera: Tachinidae) to acetamiprid, cyfluthrin, dicrotophos, indoxacarb, oxamyl, and thiamethoxam was compared in residual and oral toxicity tests. In the residual toxicity test, cyfluthrin, dicrotophos, and oxamyl were highly toxic to N. viridula. Thiamethoxam was moderately toxic to these insects. Each of the four insecticides was highly toxic to T. pennipes after prolonged tarsal contact with dried residues of these chemicals. In the oral toxicity test, where N. viridula fed on food covered with insecticide residues, none of the insecticides were toxic to adults of this stink bug, but acetamiprid, dicrotophos, and thiamethoxam were moderately toxic to the nymphs. In the oral toxicity test, where N. viridula fed on a gel-food containing insecticides, cyfluthrin, dicrotophos, oxamyl, and thiamethoxam were highly toxic to this stink bug. In an oral toxicity test using contaminated sugar water, all of the insecticides were highly toxic to T. pennipes. Because insecticides were as toxic, or more toxic, to T. pennipes than to N. viridula, it is extremely important to conserve this parasitoid by applying these insecticides for control of southern green stink bugs only when the pest reaches economic threshold.

Susceptibility of Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae) to Field Rates of Selected Cotton Insecticides

The parasitoid Cotesia marginiventris (Cresson) was treated topically with minimum recommended field rates of formulated insecticides commonly used in cotton insect control. The 14 insecticides were acephate, azinphosmethyl, bifenthrin, cyhalothrin, cypermethrin, endosulfan, esfenvalerate, fipronil, methomyl, methyl parathion, oxamyl, profenofos, thiodicarb, and AC 303,630. Eleven of the 14 insecticides were extremely toxic to C. marginiventris, causing 80 to 100% mortality of adult wasps, whereas treatment with thiodicarb, oxamyl, and acephate resulted in lower mortality of C. marginiventris males and females. For both male and female C. marginiventris, thiodicarb and oxamyl were less toxic than acephate. Esfenvalerate was the least toxic pyrethroid for C. marginiventris females. Of the three insecticides used in boll weevil control (oxamyl, azinphosmethyl, and methyl parathion), oxamyl was the least toxic to C. marginiventris. Selective use of the insecticides which result in higher survival could facil...

Susceptibility of Microplitis croceipes and Cardiochiles nigriceps (Hymenoptera: Braconidae) to Field Rates of Selected Cotton Insecticides

Microplitis croceipes (Cresson) and Cardiochiles nigriceps Vierick, parasitoids of Heliothis virescens (F.), were treated topically with field rates of 14 formulated insecticides commonly used in c...

Predation of Stink Bugs (Hemiptera: Pentatomidae) by a Complex of Predators in Cotton and Adjoining Soybean Habitats in Georgia, USA

Abstract Stink bugs (Hemiptera: Pentatomidae) are economic pests of cotton and soybean. This study was conducted to examine predation on stink bugs by arthropod predators in cotton and adjoining soybean habitats. Gut-content analysis based on polymerase chain reaction (PCR) was used to detect stink bug deoxyribonucleic acid (DNA) in predators collected from both crops over a 5 wk period. Nezara viridula (L.), Euschistus servus (Say), Chinavia hilaris (Say), and Euschistus quadrator Rolston were detected on soybean and cotton. Piezodorus guildinii (Westwood) and Thyanta custator custator (F.) were detected only on soybean whereas Euschistus tristigmus (Say) was detected only on cotton. Over both crops, 13 predators screened positive for a variety of stink bug species DNA by PCR analysis: Geocoris punctipes (Say) and Geocoris uliginosus (Say) (Hemiptera: Geocoridae), Orius insidiosus (Say) (Hemiptera: Anthocoridae), Hippodamia convergens Guérin-Méneville, Harmonia axyridis (Pallas) (cotton), and Scymnus sp. (cotton) (Coleoptera: Coccinellidae), Oxyopes salticus Hentz and Peucetia viridans (Hentz) (cotton) (Araneae: Oxyopidae), Solenopsis invicta Buren (Hymenoptera: Formicidae), Podisus maculiventris (Say) (Hemiptera: Pentatomidae), Mecaphesa asperata (Hentz) (Araneae: Thomisidae), Zelus renardii Kolenati (Hemiptera: Reduviidae), and Notoxus monodon (F.) (cotton) (Coleoptera: Anthicidae). In soybean, the percentage of G. punctipes and G. uliginosus screening positive for N. viridula was high, 87.3%, whereas the percentage screening positive for E. servus was moderately high, 60.3%. In cotton, the percentage of N. viridula DNA in gut-contents of O. insidiosus was high, 91.6%. Detection of P. guildinii and/or T. c. custator DNA in predators in cotton and of E. tristigmus DNA in predators in soybean demonstrated predator dispersal between soybean and cotton. In soybean, the percentage of P. guildinii DNA in gut contents of G. punctipes, G. uliginosus, and O. insidiosus, including those individuals in cotton that dispersed from soybean, was high. We conclude that a complex of arthropod predators prey on a complex of stink bugs in both cotton and adjoining soybean while foraging in and between these crops.

Factors Affecting Parasitization of Spodoptera exigua (Lepidoptera: Noctuidae) and Sex Ratio of the Parasitoid Cotesia marginiventris (Hymenoptera: Braconidae)

Biological factors hypothesized to affect parasitization by Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), an endoparasitoid of larvae of the beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), as well as its sex ratio, were examined in the laboratory. Highest parasitization occurred when (1) adult female parasitoids were closely associated with hosts, (2) adult female parasitoids were 1 day old, (3) a host:female parasitoid ratio of between 10:1 and 30:1 was maintained, (4) second-instar beet armyworms were used as hosts, and (5) adult female parasitoids were exposed to hosts for 24 h. Percentage of female progeny was higher when females were closely associated with second instars.

Diversity of Stink Bug (Hemiptera: Pentatomidae) Egg Parasitoids in Woodland and Crop Habitats in Southwest Georgia, USA

Abstract Euschistus servus (Say), Chinavia hilaris (Say), and Nezara viridula (L.) (Hemiptera: Pentatomidae) are economic pests of row crops. They move within and between closely associated crop and non-crop habitats throughout the growing season in response to deteriorating suitability of their current host plants. This study was conducted to investigate parasitism of naturally occurring C. hilaris and E. servus eggs in woodland habitats and crops alongside these habitats in southwest Georgia, USA. Also, parasitism of sentinel eggs of N. viridula was examined in a woodland habitat. Ten species of parasitoids, including 7 scelionids, 2 eupelmids, and 1 encyrtid, parasitized E. servus eggs. Telenomus podisi Ashmead (Hymenoptera: Scelionidae) was the most prevalent parasitoid of E. servus eggs in each of 3 habitats: woodlands, an early-season crop, and late-season crops. In woodlands, 27.9% of E. servus eggs were parasitized by Anastatus reduvii (Howard) and A. mirabilis (Walsh & Riley) (Hymenoptera: Eupelmidae). Four species of parasitoids, including 1 scelionid, 2 eupelmids, and 1 encyrtid, parasitized C. hilaris eggs. Trissolcus edessae Fouts (Hymenoptera: Scelionidae) was the most prevalent parasitoid of C. hilaris eggs in woodlands and the only parasitoid of C. hilaris eggs in late-season crops. In woodlands, 40.7% of C. hilaris eggs were parasitized by A. reduvii and A. mirabilis. In a woodland habitat, 6.6% of N. viridula sentinel eggs were parasitized by A. reduvii females, Anastatus males, and 1 encyrtid. Anastatus species were the only parasitoids that existed primarily in woodland habitats. In conclusion, a diversity of parasitoid species parasitizes native stink bug eggs in southwest Georgia, and species of parasitoids emerging from stink bug eggs can vary by habitat.