Interaction Between Entomopathogenic Fungi and Some Aphid Species in Thailand

Seven aphid species were screened with twelve entomopathogenic fungi for the selection of the most effective fungus. Beauveria bassiana CKB-048 caused the highest mortalities for all aphid species tested in their nymphal stage. The cowpea aphid (Aphis craccivora Koch) was chosen for further studies in its adult stage using B. bassiana CKB-048 as a biocontrol agent, and carbosulfan was used for a comparison in greenhouse testing. The mode of action of the fungal killing was studied by scanning electron microscopy. The endophytic colonization of the cowpea plant by B. bassiana CKB-048 was studied and confirmed using both stereo microscopy and transmission electron microscopy. The chitinase enzyme activity of cowpea plants after they were sprayed with the fungus or carbosulfan was found to fluctuate throughout five days. The lethal concentrations of B. bassiana CKB-048 suspensions that killed 50 % (LC₅₀) of A. craccivora was 6.69 × 10⁷ conidia/ml for the nymphs and 8.25 × 10⁷ conidia/ml for the adults. The time for lethality (LT₅₀) with a concentration of 2 × 10⁸ conidia/ml was 3.25 days for nymphs and 4 days for adults.     

Identification of ALS inhibitor‐resistant Amaranthus biotypes using polymerase chain reaction amplification of specific alleles

Summary Polymerase chain reaction (PCR) amplification of specific alleles (PASA) was adapted as a molecular marker‐based method for the rapid detection of point mutations in Amaranthus retroflexus and Amaranthus rudis leading to ALS inhibitor resistance. Two pairs of primers were designed for the specific amplification of alleles of the ALS gene of susceptible and resistant biotypes. The allele‐specific primer matched the desired allele, but mismatched the different allele at its 3′ end. Differentiation was carried out by comparison of the amplified DNA fragments in gel electrophoresis after PASA‐PCR. In A. rudis, differentiation was possible with one PCR and genomic DNA as probe. A ‘nested’ PCR was necessary for the differentiation of sensitive and resistant A. retroflexus. PASA is useful for the identification of resistant weed biotypes and also as a monitoring tool to map resistance occurrence and distribution. Advantages include the fast and clear separation of those plants with and without mutations at an early stage of development, its easy and consistent performance and quick results compared with existing resistance detection tests. These advantages, when combined with management strategies, enable further activities to reduce herbicide resistance.     

The effect of salt stress on Arabidopsis thaliana and Phelipanche ramosa interaction

Salinity and Orobanche or Phelipanche spp. infection are important crop stress factors in agricultural areas. In this study, we investigated the effect of salt stress on Phelipanche ramosa seed germination and its attachment onto Arabidopsis thaliana roots. We also evaluated the effect of both stresses on the expression of genes regulated by abiotic and biotic stresses. According to our results, high concentration of NaCl delayed P. ramosa seed germination in the presence of a strigolactone analogue (GR24). A similar pattern was observed in the presence of A. thaliana plants. Furthermore, we found that salt‐treated A. thaliana seedlings were more sensitive to P. ramosa attachment compared with the untreated plants, indicating that there was a positive correlation between salt sensitivity and the ability of P. ramosa to infect A. thaliana plants. At the molecular level, a synergystic effect of both salt and P. ramosa stresses was observed on the cold‐regulated (COR) gene expression profile of treated A. thaliana seedlings. Our data clarify the interaction between parasitic plants and their hosts under abiotic stress conditions.     

The dimpling bug,Campylomma austrina Malipatil (Hemiptera: Miridae): the damage and its relationship with ants in mango orchards in the Northern Territory of Australia

The dimpling bug, Campylomma austrina Malipatil, has been recognised since 2002 as a serious mango pest in the Northern Territory, Australia. To fully understand the damage the bug causes and its relationship with ants, field experiments were conducted in five mango orchards in the Darwin area from 2001 to 2003 along with laboratory rearing trials. The latter revealed that the dimpling bug sucked sap mainly from the ovary of the flowers. As the ovary ripened, each puncture resulted in a black pimple on the skin of the marble-sized fruit (<5 mm in diameter). All of the most heavily damaged marble-sized fruits (>10 pimples/fruitlet) dropped from the trees. A field survey and field experiments showed that marble-sized fruit damage levels on trees bearing abundant weaver ants, Oecophylla smaragdina Fabricius, were similar to those protected by chemical insecticides, however both suffered less damage than trees bearing fewer or no weaver ants or black ants, Iridomyrmex sp. We propose that the weaver ant is an efficient bio-control agent of the dimpling bug, and to limit the bug damage, high levels of weaver ant populations are required in mango orchards.     

Thieves,bats and fruit flies: local ecological knowledge on the weaver ant Oecophylla longinoda in relation to three ‘invisible’ intruders in orchards in Guinea

We held interviews with 100 mango and cashew growers in Guinea, West Africa. Fewer than 20 questions dealing with the tree-inhabiting weaver ant Oecophylla longinoda were developed, based on local context and related research conducted on farmers' knowledge in other countries. More than half of the growers reported that ants protect their orchard from thieves. Apart from deterring snakes, about 46% of the growers mentioned that weaver ants reduce damage by fruit-eating bats; some reported that bats do dislike the smell of weaver ants. Whereas the relationship between ants and humans or conspicuous fruit bats is well understood, a quantitative appreciation of the effect of Oecophylla on small insect pests, such as fruit flies, is more complex. Despite the fact that 57% of the growers reported that Oecophylla had a positive effect on mango fruit quality, many classified Oecophylla as a pest due to its nuisance during harvest, and they requested the plant protection staff to help them with pesticides. Strategies to strengthen local ecological knowledge are discussed.     

Carry over of bruchid,Caryedon serratus (Olivier) (Coleoptera) from field to stores through seeds of Acacia nilotica (L.) Willd. in India

Abstract

A percentage pod damage of 6.8% in Acacia nilotica (L.) Willd. by the bruchid, Caryedon serratus (Olivier) in the field was recorded by examining exit holes on the pods. The mean number of females and males that emerged from 50 pods kept in laboratory were 1.3 and 1.2 respectively. The pods of A. nilotica gathered from the field for seed purposes were found to be infested in small numbers but the bruchid population increased during storage. The infestation of seeds and carry over to stores is not only a danger to uninfested seeds of A. nilotica and other plants, important in social forestry, but the tree also acts as secondary host for the population build‐up of C. serratus which spreads to its primary host, the groundnut, Arachis hypogea (L).     

Low root‐to‐root transmission of a tobamovirus,yellow tailflower mild mottle virus,and resilience of its virions

Tobamoviruses are serious pathogens because they have extremely stable virions, they are transmitted by contact, and they often induce severe disease in crops. Knowledge of the routes of transmission and resilience of tobamovirus virions is essential in understanding the epidemiology of this group of viruses. Here, an isolate of the tobamovirus yellow tailflower mild mottle virus (YTMMV) was used to examine root‐to‐root transmission in soil and in a hydroponic growth environment. Root‐to‐root transmission occurred rarely, and when it occurred plants did not exhibit systemic movement of the virus from the roots to the shoots over a 30‐day period. The resilience of YTMMV virions was tested in dried leaf tissue over time periods from one hour to one year under temperatures ranging from ?80 to 160 °C. Infectivity was maintained for at least a year when incubated at ?80 or 22 °C, or at fluctuating ambient temperatures of 0.8 to 44.4 °C, but incubation under dry conditions at 160 °C for >4 days eliminated infectivity. Exposure of virions to 0.1 m sodium hydroxide or 20% w/v skimmed milk solution for 30 min, treatments recommended for tobamovirus inactivation, did not abolish infectivity of YTMMV.     

Isotope-edited nuclear magnetic resonance: novel methodologies for investigating metabolism

While the use of NMR and stable isotopes in metabolism studies is hardly new, it is only recently that isotope-edited NMR spectroscopy has been applied in kinetic studies of glyphosate metabolism of soil microbes. NMR can detect multiple species simultaneously and non-destructively, yielding valuable information on structural identification of metabolites. T riple R esonance I sotope ED ited spectroscopy (TRIED), [²H]NMR, and [²H–¹³C] INEPT (I nsensitive N ucleus E nhancement through P olarization T ransfer) are three isotope-edited techniques which have been used in combination to examine the microbial degradation of glyphosate (N-phosphonomethylglycine). Using ¹³C- and ¹⁵N-labeled glyphosate, TRIED can detect multiple metabolites in crude matrices at submicrogram levels, an improvement over earlier techniques where milligrams were needed. It can detect 500 nanograms of ¹³C–¹⁵N-labeled compound in a crude sample (1 : 1400 mass ratio), only a few hours work being required. [²H]NMR and [²H–¹³C]INEPT were also used as complementary techniques to further examine metabolites whose ¹³C–¹⁵N bond has been cleaved. The three-isotope-edited methods produced results consistent with both radioactivity and HPLC analyses. Accordingly, we are able to detect minute levels of metabolites in the presence of complex mixtures, minimizing the costs and time of sample purification. ©1999 Society of Chemical Industry