Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae).

The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a major insect pest of stored grain. This study evaluated resistance of grain of 26 sorghum genotypes, Sorghum bicolor (L.) Moench, to maize weevil under laboratory conditions. Three female and two male newly emerged maize weevils were reared with 5 g of grain in each of 10 vials for each of the 26 sorghum genotypes in a laboratory experiment. The weevils and grain of each genotype were scored once every 3 wk for a total of five times during 105 d. The numbers of live and newly emerged maize weevils, dead weevils from the initial population, damage score (scale of 1-5), and grain weight loss were used to indicate resistance. The least percentage weight loss of 23.9 and 24.1% was recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had the most weight loss, 70.6 and 67.7%, at 105 d after infestation. Genotypes B.HF8 and (A964*P850029)-HW6 consistently exhibited the highest numbers of maize weevil, 63 and 84, per vial at 105 d after infestation. Sorghum genotypes Sureño, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotype across the five sampling dates. On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with the highest damage rating. Our results indicate that grain of genotype Sureno is most resistant to the maize weevil among screened genotypes.

Evaluation of Host-Plant Resistance of Selected Rice Genotypes to the Rice Water Weevil (Coleoptera: Curculionidae).

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important insect pest of rice in the United States. Management of L. oryzophilus mainly depends upon the use of insecticides due to the lack of effective alternative management tactics. A 3-yr field study was conducted to determine if difference exists among rice genotypes and cultivars of inbred tropical japonica subspecies commercially grown in the southern United States [Cocodrie (PI 606331), CL171, and CL151 (PI 654463)] and the germplasm lines of indica subspecies adapted to tropical climates of Asia [WC 4644 (PI 312777), TNI (PI 495830), Rondo (PI 615022), 4612 (PI 615039), TeQing (PI 536047), and 4593 (PI 615031)] for resistance to L. oryzophilus Experiments were established as a split-plot design with cultivars as main plots and insecticide treatment as subplots. No significant differences were observed in number of L. oryzophilus larvae recovered across cultivars and genotypes, indicating no significant variation in their preference to L. oryzophilus oviposition. Insecticide treatment had a significant impact on L. oryzophilus larval density. However, grain yield did not vary significantly between treated and untreated plots for any of the cultivars and genotypes. The amount of yield loss in response to L. oryzophilus infestation did not vary significantly across genotypes and cultivars, indicating no variation among these genotypes for resistance to L. oryzophilus.

Redbanded Stink Bug (Hemiptera: Pentatomidae) Infestation and Occurrence of Delayed Maturity in Soybean.

Studies done in Brazilian soybean, Glycine max (L.) Merril, in the 1970s suggested the redbanded stink bug, Piezodorus guildinii (Westwood), is principally responsible for delayed maturity in this crop. This stink bug species has recently emerged as a serious pest of soybean in the southern United States, where little is known about its association with the occurrence of delayed maturity disorder. Also, the mechanism behind stink bug-induced soybean delayed maturity remains unknown. It is believed that stink bug feeding during pod development stages results in reduced pod-seed load, causing alteration of source-sink ratio and eventually delayed maturity. To determine the P. guildinii threshold triggering delayed maturity in soybean, experiments were conducted with varying levels of P. guildinii infestation (0, 2, 4, and 8 adults per 0.3 m) during the R4 to R5 soybean growth stages. In addition, to determine if soybean delayed maturity is exclusively because of reduced pod load, experiments with different levels of mechanical pod removal (0, 25, 50, and 75%) were conducted on field-grown soybeans. P. guildinii densities up to 4 adults per 0.3 m did not trigger occurrence of delayed maturity. However, a density of 8 adults per 0.3 m produced a significant increase in the number of green leaves retained on plants at maturity (i.e., delayed maturity). There was no effect of mechanical pod removal on green leaf retention. The lack of a significant positive correlation between mechanical pod removal and green leaf retention indicates the involvement of mechanism(s) other than reduced pod load in the occurrence of soybean delayed maturity.

Determination of Growth Stage-Specific Response of Soybean to Redbanded Stink Bug (Hemiptera: Pentatomidae) and its Relationship to the Development of Flat Pods.

The redbanded stink bug, Piezodorus guildinii Westwood (Hemiptera: Pentatomidae), has recently emerged as a serious pest of soybean in the southern United States. Field cage studies were conducted to determine the response of R2 to R6 stage soybean to P. guildinii infestation. Soybean at R2 to R6 stages was infested with zero, one, two, and four P. guildinii adults per 0.3 m for 10 d using cylindrical wire mesh cages. Plant response was measured in terms of number of flat pods, seed yield, test weight, and number of seeds per pod. Results from a 2012 study showed significant yield reduction in response to P. guildinii infestations during the R3 to R6 stages. While results from a similar 2013 study showed a significant yield reduction only when R5 and R6 stage soybean were infested. Decrease in yield was owing to the combination of reduced seed weight and increased numbers of flat pods as a result of P. guildinii infestation. In addition, a field experiment was conducted to determine if flat pods are localized to the regions of P. guildinii feeding. Adults were confined to certain portions of plants (bottom, top, and both) using specially designed cages isolating these portions of the plants. Results from this experiment showed a significantly higher percentage of flat pods on plant portions infested with P. guildinii than those kept free of P. guildinii infestation, indicating that flat pods are the result of direct P. guildinii damage and are localized to the area of P. guildinii feeding.

Stink bug species composition and relative abundance of the redbanded stink bug (Hemiptera: Pentatomidae) in soybean in the upper gulf coast Texas.

Stink bugs are the primary arthropod soybean pests in the southern United States. Historically, important stink bug species damaging soybeans in the southern United States included the southern green stink bug Nezara viridula (L.), the green stink bug Chinavia hilaris (Say), and the brown stink bug Euschistus servus (Say) (Hemiptera: Pentatomidae). The redbanded stink bug, Piezodorus guildinii (Westwood), has recently become an economic pest of soybean in the southern region of the United States, especially in Louisiana and Texas. Little is known about current stink bug species composition and relative abundance in Texan soybean agro-ecosystems. To fill this gap, commercial soybean fields in the Upper Gulf Coast of Texas were sampled weekly during the growing season using a sweep net throughout R2 (full flowering) to R7 (beginning maturity) from 2011 to 2013. Adults and nymphs (third, fourth, and fifth instars) of redbanded stink bug, southern green stink bug, green stink bug, and brown stink bug were counted per 25 sweeps. The relative abundance of redbanded stink bug was significantly higher than any other stink bug species throughout 2011-2013. Over 65% of the total population of major stink bugs collected during this period were redbanded stink bugs and ≍19% were southern green stink bugs. The highest redbanded stink bug densities and the highest ratio of redbanded stink bug nymphs to adults were recorded at R7. Results from this study show that redbanded stink bug has become the predominant stink bug species in soybean in the Upper Gulf Coast of Texas.