Hardev S. Sandhu

Temperature-Dependent Development of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on Sugarcane Under Laboratory Conditions

ABSTRACT Lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), is an important sugarcane pest in southern Florida. Development of immature stages (eggs, larvae, prepupae, and pupae) of lesser cornstalk borer was observed on sugarcane at constant temperatures (13, 15, 18, 21, 24, 27, 30, 33, and 36°C), 65–70% RH, and a photoperiod of 14:10 (L:D) h. Total development (from egg deposition to adult emergence) ranged from 22.8 ± 0.3 d at 33°C to 120.7 ± 2.8 d at 13°C. Lesser cornstalk borer required 543.48 DD to complete development. Developmental time decreased with increase in temperature from 13 to 33°C and increased markedly at 36°C in all immature stages. One linear and six nonlinear models used to model insect development (Briere-1, Briere-2, Logan-6, Lactin, Taylor, and polynomial models) were tested to describe the relationship between temperature and developmental rate (d-1). Criteria used to select the best model were the greatest r2, lowest residual sum of squares (RSS), and Akaike information criterion values. The Briere-1 model fit the data best and provided the best estimates of developmental temperature thresholds for all immature stages on sugarcane. The estimated lower and upper developmental thresholds for total development were 9.3 ± 1.8 and 37.9 ± 0.7°C, respectively. The optimal temperature estimated for the total development was 31.39 ± 0.9°C. Based on these results, we can forecast the different stages of lesser cornstalk borer at different times in sugarcane. This will enable us to choose the best time to control this pest with greater precision.

Applications of the Bootstrap to Insect Physiology

ABSTRACT The effect of temperature on development and the effect of photoperiod on diapause incidence of insects are common topics in insect physiology. Related to these topics, are 3 important concepts: the lower and upper developmental thresholds, which represent the lower and upper limits of thermal range for insects to develop, and the critical photoperiod, which causes diapause in 50% of a population. To compare lower or upper developmental thresholds of 2 different developmental stages or of 2 populations at the same developmental stage is difficult because of the lack of a suitable statistical method. Shi et al. (2010) proposed 2 methods for testing whether there is a significant difference between 2 lower developmental thresholds. However, these 2 methods are only applicable to the linear relationship between developmental rate and temperature. There are also many studies on the geographic variation in the critical photoperiods for different populations of an insect species. Also, a method is lacking for testing whether there is a significant difference between 2 critical photoperiods. In this study, we test bootstrap to determine if there is a significant difference between different parameters. Bootstrap can then be used to compare any 2 lower or upper developmental thresholds, or to compare 2 critical photoperiods. It can also provide the confidence interval of a critical photoperiod.

Comparison of dwarf bamboos (Indocalamus sp.) leaf parameters to determine relationship between spatial density of plants and total leaf area per plant

Abstract The relationship between spatial density and size of plants is an important topic in plant ecology. The self‐thinning rule suggests a −3/2 power between average biomass and density or a −1/2 power between stand yield and density. However, the self‐thinning rule based on total leaf area per plant and density of plants has been neglected presumably because of the lack of a method that can accurately estimate the total leaf area per plant. We aimed to find the relationship between spatial density of plants and total leaf area per plant. We also attempted to provide a novel model for accurately describing the leaf shape of bamboos. We proposed a simplified Gielis equation with only two parameters to describe the leaf shape of bamboos one model parameter represented the overall ratio of leaf width to leaf length. Using this method, we compared some leaf parameters (leaf shape, number of leaves per plant, ratio of total leaf weight to aboveground weight per plant, and total leaf area per plant) of four bamboo species of genus Indocalamus Nakai (I. pedalis (Keng) P.C. Keng, I. pumilus Q.H. Dai and C.F. Keng, I. barbatus McClure, and I. victorialis P.C. Keng). We also explored the possible correlation between spatial density and total leaf area per plant using log‐linear regression. We found that the simplified Gielis equation fit the leaf shape of four bamboo species very well. Although all these four species belonged to the same genus, there were still significant differences in leaf shape. Significant differences also existed in leaf area per plant, ratio of leaf weight to aboveground weight per plant, and leaf length. In addition, we found that the total leaf area per plant decreased with increased spatial density. Therefore, we directly demonstrated the self‐thinning rule to improve light interception.

Temperature-Dependent Reproductive and Life Table Parameters of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on Sugarcane

ABSTRACT The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Reproductive and life table parameters for E. lignosellus were examined at nine constant temperatures from 13 to 36 °C with sugarcane as the larval food source. The pre- and post-oviposition periods decreased with increasing temperatures and reached their minimums at 33 and 36 °C, respectively. The oviposition period was longest at 27 °C. The mean fecundity, intrinsic rate of increase (r), and finite rate of increase (&lgr;) were greatest at 30 °C and decreased with increasing or decreasing temperature. The net reproductive rate (R0) was greatest at 27 °C. The Brière-1 model best described the relationship between temperature and r. The generation (T) and population doubling times (DT) were shortest at 33 and 30 °C, respectively. The temperatures around 27 to 30 °C are most favorable for E. lignosellus population growth and significant damage can be expected under these climatic conditions. This data in combination with population monitoring of E. lignosellus under field conditions can be effectively used in population predictions of this pest in field and severe damage can be prevented by timely implementation of control measures.

Population decrease of Scirpophaga incertulas Walker (Lepidoptera Pyralidae) under climate warming.

Scirpophaga incertulas Walker is an important agricultural pest in Asia. Only few studies are available on its long-term population dynamics under climate warming. In this study, we used the linear and generalized additive models (GAMs) to analyze the historical dataset of >50 years on this pest at Xinfeng County of Jiangxi Province, China. The main objective of this study was to explore the effects of density (delayed) dependence and minimum annual temperature (MAT), which indirectly reflects climate warming, on the population dynamics of this pest. We found that both density dependence and MAT have significant influence on the annual population growth rate. The GAMs had relatively better applicability to the dataset than the linear models. Nonparametric model provided satisfactory goodness-of-fit (R2 > 0.5). At Xinfeng County, the MAT had a significant effect on the annual population growth rate of S. incertulas. The annual population growth rate of S. incertulas decreased with increase in MAT. Therefore, S. incertulas population becomes smaller and smaller in Southern China due to climate warming. The current study has two contributions: (1) providing a suitable method for predicting the annual population growth rate of S. incertulas, and (2) demonstrating that climate warming could decrease the S. incertulas population.

Life table studies of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on sugarcane.

ABSTRACT This article has been withdrawn at the request of the authors due to numerous errors that cannot readily be corrected by publishing an erratum. The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Reproductive and life table parameters for E. lignosellus were examined at nine constant temperatures from 13 to 36°C with sugarcane as the larval food source. The pre- and postoviposition periods decreased with increasing temperatures and reached their minimums at 33 and 36°C, respectively. The oviposition period was longest at 27°C. The mean fecundity, stage-specific survival, stage-specific fecundity, intrinsic rate of increase, and finite rate of increase were greatest at 30°C and decreased with increasing or decreasing temperature. The net reproductive rate was greatest at 27°C. The Logan-6 model best described the relationship between temperature and intrinsic rate of increase. The generation and population doubling times were longest at 13 and shortest at 33 and 30°C, respectively. The most favorable temperatures for E. lignosellus population growth were between 27 and 33°C. Life table parameters for E. lignosellus reared on sugarcane were greater than for the Mexican rice borer [Eoreuma loftini (Dyar) (Lepidoptera: Crambidae)] reared on an artificial diet at 30°C. The intrinsic rates of increase for the sugarcane borer [Diatraea saccharalis (F.) (Lepidoptera: Crambidae)] reared on sugarcane or corn were the same as for E. lignosellus reared on sugarcane at 27°C, but the net reproductive rate was four times higher for the former than the latter borer species. This article has been withdrawn.

Population dynamics and associated factors of cereal aphids and armyworms under global change.

Studying the impacts of global change, which comprises largely climate and landscape changes, on agricultural pests is crucial for developing sustainable pest management. This research is focused on understanding the factors associated with population dynamics of cereal aphids and armyworms feeding on wheat in Henan province in China from 1987 to 2010. Association between changes in climate (temperature, precipitation, and relative humidity) and agricultural characteristics (wheat proportion, crop diversity, fertilizer input, and wheat yield per unit area) and damage from cereal aphids and armyworms were examined. Cereal aphid damage has been rising, while armyworm damage had no obvious trends, but with strong year-to-year fluctuations. The analysis indicates that the factors most strongly associated with the population dynamics of cereal aphids are fertilizer input and mean temperature in February, while the population dynamics of armyworms is significantly related to precipitation in May. By comparing the characteristics of these two agricultural pests, we identify possible reasons for the disparity between their associated factors, which are related to the differences in their foraging behaviour, host range, migration capacity, and life history. These results may contribute to developing ecologically based pest management for cereal aphids and armyworms under global change.

Shifts in natural enemy assemblages resulting from landscape simplification account for biocontrol loss in wheat fields

In recent decades, landscape simplification due to agricultural intensification has resulted in biocontrol loss within agroecosystems leading to an increase in pest outbreaks. Empirical experiments have focused on the relationship between landscape pattern and the abundance of specific species. However, fewer studies have examined the varied responses of multiple natural enemy modules to landscape simplification. In the present study, 23 landscapes were examined to determine the effects of landscape simplification on cereal aphids and their natural enemies. Results showed that landscape simplification can increase cereal aphid populations with no significant effects on the total abundance of natural enemies. For each natural enemy module, it was found that the abundance of parasitic wasps was greatly increased by landscape simplification while the abundance of ground-dwelling predators was significantly reduced. In contrast, the abundance of leaf-dwelling predators was not significantly altered by landscape simplification. Therefore, the varied response of the three natural enemy modules to landscape simplification can result in major fluctuations in natural enemy–pest ratios and ultimately disrupt the top-down control of natural predators and biocontrol services within agroecosystems. In conclusion, quantitative food-web analysis could be a promising technique in clarifying the varied response of the three natural enemy modules to landscape pattern changes and species-specific abundance, a field of biological pest control that requires further study.

Effects of Harvest Residue and Tillage on Lesser Cornstalk Borer (Lepidoptera: Pyralidae) Damage to Sugarcane

ABSTRACT Lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Cultural controls for E. lignosellus were evaluated in preparation for the potential loss of effective insecticides. Field studies conducted in 2006 compared the effects of harvest residues from green-harvested sugarcane (no preharvest burning to remove leaf matter) on E. lignosellus stalk damage and yield. Damage by E. lignosellus was significantly lower in plant cane plots that were covered with harvest residues collected from a green-harvested field before shoot emergence compared with plots without harvest residue. There were no yield differences between plots with and without harvest residues in plant or ratoon sugarcane fields in the 2006 study. The effects of three postharvest tillage levels (conventional, intermediate, and no tillage) were evaluated in preharvest burned and green-harvested fields in 2008 and 2009. Significantly less E. lignosellus damage was observed in the green- versus preharvest burned fields in both years. Intermediate and no-tillage plots had very little damage in green-harvested field. Conventional tillage plots had the greatest damage in the green-harvested field and the lowest damage in the preharvest burned field. In 2008, biomass yield was greater in the intermediate than conventional tillage in the green-harvested field, but it was greater in the conventional than in other tillage levels in the preharvest burned field. These studies demonstrated that cultural controls could greatly reduce E. lignosellus damage in sugarcane without the use of insecticides.

Landscape changes have greater effects than climate changes on six insect pests in China

In recent years, global changes are the major causes of frequent, widespread outbreaks of pests in mosaic landscapes, which have received substantial attention worldwide. We collected data on global changes (landscape and climate) and economic damage caused by six main insect pests during 1951–2010 in China. Landscape changes had significant effects on all six insect pests. Pest damage increased significantly with increasing arable land area in agricultural landscapes. However, climate changes had no effect on damage caused by pests, except for the rice leaf roller (Cnaphalocrocis medinalis Guenee) and armyworm (Mythimna separate (Walker)), which caused less damage to crops with increasing mean temperature. Our results indicate that there is slight evidence of possible offset effects of climate changes on the increasing damage from these two agricultural pests. Landscape changes have caused serious outbreaks of several species, which suggests the possibility of the use of landscape design for the control of pest populations through habitat rearrangement. Landscape manipulation may be used as a green method to achieve sustainable pest management with minimal use of insecticides and herbicides.