Temporal Dynamics of Corn Flea Beetle Populations Infested with Pantoea stewartii, Causal Agent of Stewart's Disease of Corn

ABSTRACT In order to better understand the epidemiology of the Stewart's disease of corn pathosystem, quantitative information concerning the temporal dynamics of the amount of pathogen inoculum present in the form of Pantoea stewartii-infested corn flea beetles (Chaetocnema pulicaria) is needed. Temporal changes in the proportion of P. stewartii-infested corn flea beetle populations were monitored by testing individual corn flea beetles for the presence of P. stewartii using a peroxidase-labeled, enzyme-linked immunosorbent assay. Approximately 90 corn flea beetles were collected each week from seven locations in Iowa from September 1998 through October 2000 using sweep nets. The proportion of P. stewartii-infested beetles at the end of the 1998 growing season ranged from 0.04 to 0.19. In spring 1999, the proportion of overwintering adult corn flea beetles infested with P. stewartii ranged from 0.10 to 0.11 and did not differ significantly from the previous fall based on chi(2). During the 1999 corn-growing season, the proportion of infested corn flea beetles ranged from 0.04 to 0.86, with the highest proportions occurring in August. In fall 1999, the proportion of beetles infested with P. stewartii ranged from 0.20 to 0.77. In spring 2000, the proportion of overwintering adult corn flea beetles infested with P. stewartii ranged from 0.08 to 0.30; these proportions were significantly lower than the proportions observed in fall 1999 at Ames, Chariton, and Nashua. During the 2000 corn-growing season, the proportion of P. stewartii-infested corn flea beetles ranged from 0.08 to 0.53, and the highest observed proportions again occurred in August. Corn flea beetle populations sampled in late fall 2000 had proportions of infested beetles ranging from 0.08 to 0.20. This is the first study to quantify the temporal population dynamics of P. stewartii-infested C. pulicaria populations in hybrid corn and provides new quantitative information that should be useful in developing risk models to predict the seasonal and site-specific risks associated with Stewart's disease of corn.     

Role of the Insect Vector, Pseudotheraptus devastans, in Cassava Anthracnose Disease Development

The aim of this study was to investigate the role of Pseudotheraptus devastans in cassava anthracnose disease transmission and development. P. devastans, Dist (Het. Coriedae) insects were collected from cassava (Manihot esculenta Crantz) field plots at the International Institute of Tropical Agriculture, Ibadan, Nigeria and reared in large cages. The insects were separated at different developmental growth stages of eggs, first to fifth instar nymph, and adults. The different stages of P. devastans showed the presence of Colletotrichum gloeosporioides both externally and internally. Isolates of C. gloeosporioides derived from the insects produced cassava anthracnose disease symptoms (necrotic lesions, wilt and defoliation) 8 weeks after inoculation on two cassava clones. Re-infectivity of cassava plants by the insect-derived fungus established that P. devastans was a potential vector in anthracnose transmission. Except for the first and second instar nymphs, all nymph stages and adult insects produced significant anthracnose symptoms on cassava plants. Defoliation and lesion diameters were greatest using fifth instar nymphs and adult insects. The association between P. devastans feeding and C. gloeosporioides f.sp. manihotis, showed that feeding by P. devastans followed by fungal inoculation and vice versa resulted in more severe anthracnose symptoms than insect feeding or fungal inoculation alone. It was also observed that the influence of P. devastans damage/infection on the development of anthracnose depended on cassava cultivar resistance to both the fungus and the insect feeding.     

The Role of the Bark Beetle, Hylastes ater (Coleoptera: Scolytidae), as a Sapstain Fungi Vector to Pinus radiata Seedlings: A Crisis for the New Zealand Forestry Industry?

The role of the bark beetle Hylastes ater in the re-establishment of Pinus radiata forest in New Zealand is discussed. H. ater was found to be a dominant factor in seedlings mortality in the first year following planting. However, seedling mortality is usually relatively low. In contrast, it was found the large numbers of seedlings were sub-lethally damaged by H. ater feeding attempts, particularly in high risk sites. High risk sites were identified as sites that were harvested during March and April (autumn) when the peak flight activity of H. ater occurred, and subsequently planted with P. radiata seedlings the following winter. H. ater was found to vector sapstain fungi to seedlings during feeding attempts, and a strong relationship between the severity of damage and presence of sapstain fungi was identified. The role of H. ater as a vector of these fungi and the potential implications to the New Zealand forest industry are discussed.     

Infection of Commercial Hybrid Primula Seed by Botrytis cinerea and Latent Disease Spread Through the Plants

ABSTRACT Botrytis cinerea occurred commonly on cultivated Primula xpolyantha seed. The fungus was mostly on the outside of the seed but sometimes was present within the seed. The fungus frequently caused disease at maturity in plants grown from the seed, demonstrated by growing plants in a filtered airflow, isolated from other possible sources of infection. Young, commercially produced P. xpolyantha plants frequently had symptomless B. cinerea infections spread throughout the plants for up to 3 months, with symptoms appearing only at flowering. Single genetic individuals of B. cinerea, as determined by DNA fingerprinting, often were dispersed widely throughout an apparently healthy plant. Plants could, however, contain more than one isolate.     

Successful Back-inoculation Confirms the Role of Black Currant Reversion Associated Virus as the Causal Agent of Reversion Disease

Reversion is the most wide-spread and serious virus-like disease infecting black currant but the causal agent of the disease has not been described. Recently, we have isolated a new nepovirus from reversion-infected black currant and by using immunocapture-RT-PCR detection, we have shown that the virus is consistently associated with reversion disease (Lemmetty et al., Phytopathology 87: 404–413, 1997). These data suggested that the virus, tentatively called black currant reversion associated virus (BRAV), could be the causal agent of reversion disease. Here we report that the isolated virus was successfully inoculated back to healthy black currant plants by slash inoculation of in vitro propagated young recipient plants. Vein pattern symptoms identical or very similar to the reported early symptoms of reversion disease were produced in the virus-infected plants. Using immunocapture-RT-PCR, the virus was again detected from symptomatic but not from inoculated symptomless plants or from the mock-inoculated or uninoculated controls. Production of the acute reversion symptoms demonstrates that BRAV is the causal agent of reversion disease, and we therefore propose that the virus be named black currant reversion virus, abbreviated BRV.     

松褐天牛的重要捕食性天敌──天牛霉纹斑叩甲

2003年至2006年对松材线虫病的主要传播媒介昆虫--松褐天牛的天敌昆虫进行了调查,在我国广东省首次发现了松褐天牛的一种重要捕食性天敌--天牛霉纹斑叩甲(Cryptalaus berus).对天牛霉纹斑叩甲的形态特征进行了描述;在室内条件下,观察研究了该天敌的捕食能力.结果显示,1头叩甲幼虫在130d的发育期里,累计捕食、杀死了27头松褐天牛幼虫,之后开始化蛹;另1头叩甲幼虫在138d的发育期里,累计捕食、杀死了19头松褐天牛幼虫.叩甲幼虫可在松褐天牛坑道之间转移捕食.