Estimating the development of the fennel aphid, Hyadaphis foeniculi (Passerini) (Hemiptera: Aphiididae), using non-linear models

Dispersion of the soybean root rot by Cycloneda sanguinea (Coleoptera: Coccinellidae)

The dispersion of pathogenic microorganisms consists of the transport of pathogens from their source to inoculate a new host. Agricultural and economic importance of the Soybean root rot justifies studying this disease, especially the role of insects as dispersers. The aim of this study was to evaluate the role of the ladybird beetle, Cycloneda sanguinea Linnaeus (Coleoptera: Coccinellidae) in the dispersion of pathogens that cause Soybean root rot. Three pathogen species, Macrophomina phaseolina (Tassi) (Sphaeropsidales: Botryosphaeriaceae), Fusarium incarnatum-equiseti species complex (FIESC), and F. commune (Skovgaard) O'Donnell & Nirenberg were isolated from the midgut of ladybird beetles and cultured. Macrophomina phaseolina was identified by morphology while for the other two species, DNA was sequenced. The DNA extracted was amplified in the Internal Transcriber Spacer (ITS) region, sequenced and compared to voucher sequences deposited in the GenBank. Sequences of nucleotide ITS1-5.8 S were identified in the regions of rDNA-ITS4 ribosomal DNA. This is the first report of Macrophomina phaseolina (Tassi) (Sphaeropsidales: Botryosphaeriaceae), Fusarium incarnatum-equiseti species complex (FIESC), and F. commune (Skovgaard) O'Donnell & Nirenberg, being dispersed by C. sanguinea in Brazilian soybean fields.

Population dynamics of Aphis gossypii Glover and in sole and intercropping systems of cotton and cowpea

Population dynamics of aphids have been studied in sole and intercropping systems. These studies have required the use of more precise analytical tools in order to better understand patterns in quantitative data. Mathematical models are among the most important tools to explain the dynamics of insect populations. This study investigated the population dynamics of aphids Aphis gossypii and Aphis craccivora over time, using mathematical models composed of a set of differential equations as a helpful analytical tool to understand the population dynamics of aphids in arrangements of cotton and cowpea. The treatments were sole cotton, sole cowpea, and three arrangements of cotton intercropped with cowpea (t1, t2 and t3). The plants were infested with two aphid species and were evaluated at 7, 14, 28, 35, 42, and 49 days after the infestations. Mathematical models were used to fit the population dynamics of two aphid species. There were good fits for aphid dynamics by mathematical model over time. The highest population peak of both species A. gossypii and A. craccivora was found in the sole crops, and the lowest population peak was found in crop system t2. These results are important for integrated management programs of aphids in cotton and cowpea.

Estimating the development rate of the tomato leaf miner, Tuta absoluta (Lepidoptera: Gelechiidae), using linear and non-linear models

BACKGROUND

Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is native to South America and has recently invaded European, African and Asian countries, where it is causing severe damage to tomato crops leading to an increase in the number of insecticide applications. This situation has prompted a demand for alternative pest management strategies aiming to control T. absoluta and concomitantly reduce insecticide applications. The development period for immature stages of T. absoluta at constant temperatures was modelled to select appropriate mathematical functions for simulating its development.

RESULTS

The performance of the models varied according to the insect development stage, but in general all models performed well considering the statistical criteria used. Discrimination among models was possible only when the reliability of the temperature thresholds estimated by the models was used as an additional criterion. In this case, the models Briere-1, Lactin-2 and Shi proved adequate to describe the relationship between temperature and development rate of T. absoluta.

CONCLUSION

These models provide an important tool to predict the occurrence of the immature stages of T. absoluta in the field in order to determine the best period for implementing control measures. This is an important contribution to the development of pest management strategies for T. absoluta. © 2016 Society of Chemical Industry.

Temperature-Dependent Fecundity and Life Table of the Fennel Aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae)

Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) is a cosmopolitan species and the main pest of fennel in northeastern Brazil. Understanding the relationship between temperature variations and the population growth rates of H. foeniculi is essential to predict the population dynamics of this aphid in the fennel crop. The aim of this study was to measure the effect of constant temperature on the adult prereproductive period and the life table fertility parameters (infinitesimal increase ratio (rm), gross reproduction rate (GRR), net reproduction rate (R0), finite increase ratio (λ), generation time (GT), the time required for the population to double in the number of individuals (DT), and the reproduction value (RVx)) of the fennel pest H. foeniculi. The values of lx (survival of nymphs at age x) increased as the temperature rose from 15 to 28°C and fell at 30°C, whereas mx (number of nymphs produced by each nymph of age x) increased from 15 to 25°C and fell at 28 and 30°C. The net reproduction rates (R0) of populations of H. foeniculi increased with temperature and ranged from 1.9 at 15°C to 12.23 at 28°C for each generation. The highest population increase occurred with the apterous aphids at 28°C. The rate of population increase per unit time (rm) (day) ranged from 0.0033 (15°C) to 0.1995 (28°C). The highest values of rm were recorded at temperatures of 28°C and 30°C. The rm values were a good fit to the models tested, with R2 > 0.91 and R2adj > 0.88. The models tested (Davidson, Sharpe and DeMichele modified by Schoolfield et al., Logan et al., Lamb, and Briere et al.) were very good fits for the rm values observed, with R2 > 0.91 and R2adj > 0.88. The only exception was the Davidson model. Of the parameters studied, the reproductive capacity was higher in the apterous aphids, with the unique exception of daily fecundity at 28°C, which was higher in the alate aphids of H. foeniculi. Parameters relating to the age-specific fertility table for H. foeniculi were heavily influenced by temperature, with the highest biotic potential and population growth capacity found at 34°C. Therefore, the results obtained in this study could be of practical significance for predicting outbreaks of fennel aphids and improving the management of this aphid in fennel crops.