Cross-crop effects on larval growth, survivorship and fecundity of Helicoverpa armigera

The cotton bollworm Helicoverpa armigera is a destructive pest that affects a variety of crop plants. Because of its polyphagous feeding habit, mobility as adults, and high fecundity, the expanding infestations of H. armigera in different crops have caused economic losses and difficulties for pest population management. In Brazil, a sequence of different crop systems in the same area and crop rotation during the year can create a spatio-temporal mosaic of crops where H. armigera can persist. However, the consequences of the simultaneous and/or alternating presence of host plants for H. armigera populations through generations are unknown. In this study, we simulated, in the laboratory, hypothetical situations for the availability of soybean and cotton crops in the landscape. We evaluated the effects of: (1) the number of generations during which a population feeds on a host-plant species; (2) the succession of host-plant species on which populations have fed for two generations; and (3) the parental host plant on the fitness of H. armigera populations. Only the current host plant on which larvae fed affected the performance of the H. armigera populations. Decrease of mortality rates during the immature period was slowed when the larvae fed on soybean. The lowest value of reproductive potential (R0) was found for individuals originating from mating between females and males reared in cotton. Our results indicated that pest-management and biological-control plans for H. armigera should be developed on a regional scale rather than for just a specific crop area

Does the scion or rootstock of Citrus sp. affect the feeding and biology of Diaphorina citri Kuwayama (Hemiptera: Liviidae)?

The Asian citrus psyllid (ACP) Diaphorina citri is the main vector of the bacteria associated with Huanglongbing, and can exploit more than 50 species of the family Rutaceae as hosts. The number of possible hosts is even higher if plant varieties are included. This study evaluated the influence of different combinations of scion and rootstock citrus varieties on the development and feeding of ACP. Survival rates for the egg stage were highest on the Valencia and Sicilian varieties, both grafted on Sunki mandarin, with means of 87.99 and 87.98%, respectively; and lowest (67.63%) on Hamlin 9 Rangpur lime. The lowest levels of both nymphal and total viability (egg-adult) were obtained on Hamlin, regardless of the rootstock used. The total development time (egg-adult) ranged from 17.92 to 19.33 days for the Peˆra 9 Sunki and Hamlin 9 Swingle combinations, respectively. Cluster analysis separated the hosts into two groups, the first consisting of the combinations of the Hamlin variety, and the second group formed by the other varieties. The highest food value (assessed by the area of honeydew produced) was observed for the orange scion varieties, and among these, the highest value was observed on Valencia (0.902 cm2); the smallest honeydew area was obtained on Ponkan (0.269 cm2). The rootstocks did not affect the feeding behavior of D. citri. The results of this study could aid in the development of management techniques, mainly in providing information for the installation of new citrus groves and assistance in crop-improvement research

On Wald Residuals in Generalized Linear Models

A rigorous asymptotic theory for Wald residuals in generalized linear models is not yet available. The authors provide matrix formulae of order O(n(-1)), where n is the sample size, for the first two moments of these residuals. The formulae can be applied to many regression models widely used in practice. The authors suggest adjusted Wald residuals to these models with approximately zero mean and unit variance. The expressions were used to analyze a real dataset. Some simulation results indicate that the adjusted Wald residuals are better approximated by the standard normal distribution than the Wald residuals

Different Approaches for Modeling Grouped Survival Data: A Mango Tree Study

Interval-censored survival data, in which the event of interest is not observed exactly but is only known to occur within some time interval, occur very frequently. In some situations, event times might be censored into different, possibly overlapping intervals of variable widths; however, in other situations, information is available for all units at the same observed visit time. In the latter cases, interval-censored data are termed grouped survival data. Here we present alternative approaches for analyzing interval-censored data. We illustrate these techniques using a survival data set involving mango tree lifetimes. This study is an example of grouped survival data.Brazilian CAPES Foundation[BEX 0298/01-8]CNP

Validation of body condition score as a predictor of subcutaneous fat in Nelore (Bos indicus) cows

The aim of the present study was to determine the relationship among body weight (BW), body condition score (BCS) and rump fat thickness (RFAT) measured by ultrasonography, and validate the relationship between BCS and RFAT over the time. Two hundred sixty and six Nelore cows had their BW, BCS and RFAT evaluated at five different moments during the production cycle: M1) weaning: M2) parturition, M3) 42 days post-partum; M4) 82 days postpartum and M5) 112 days post-partum. A BCS value was attributed for each cow following a I to 5 points scale. Ultrasonographic images for RFAT measurement were obtained using a 3.5 MHz linear transducer. Images were immediately analyzed as soon as they were formed and frozen. Body condition scores and ultrasound measurements were collected on the same day by a single trained technician. The relationship between BCS and RFAT values was investigated by regression models. The analysis of similarity among the five obtained models was performed using the proc MIXED from SAS and the correlations among variables were analyzed with proc CORR from SAS. The BCS was able to predict RFAT in Nelore cows in all different moments evaluated. Also, it was shown that BCS presented high correlation (r=0.82 to 0.93) and relationship (R(2) = 0.73 to 0.92) with RFAT. However, both BCS and RFAT showed low correlation (r=0.37 to 0.50) and relationship (R(2) = 0.13 to 0.25) with BW. The BCS classification by visual method using a 1 to 5 point scale, was able to predict the RFAT in Nelore cows over the time. (C) 2008 Elsevier B.V. All rights reserved.FAPESP[05/57425-7