Mukesh K. Dhillon

Influence of seed treatment and abiotic factors on damage to Bt and non-Bt cotton genotypes by the serpentine leaf miner Liriomyza trifolii (Diptera: Agromyzidae)

In recent years, the serpentine leaf miner Liriomyza trifolii (Burgess) has become a major pest of cotton (Gossypium spp.) in India, with high levels of incidence observed at the seedling stage, particularly in transgenic Bt cotton. We monitored the severity of infestation and damage by L. trifolii to transgenic and non-transgenic genotypes of Gossypium arboreum L. and G. hirsutum L. between 2002 and 2007. Overall, significantly lower L. trifolii damage occurred in G. arboreum varieties than in G. hirsutum varieties and hybrids. Among the G. hirsutum genotypes, damage was significantly lower in varieties than in hybrids. However, no significant differences in damage were observed between Bt and non-Bt cotton hybrids. Abiotic factors had a major influence on the severity of damage; there was a significant and negative association of L. trifolii damage with open pan evaporation (E), maximum temperature, solar radiation and sunshine, and a significant and positive association with relative humidity and rainfall (RF). Multiple stepwise regression analysis indicated that 99% of the variation in L. trifolii damage was accounted for by RF, open pan E and relative humidity.

Bridging Conventional and Molecular Genetics of Sorghum Insect Resistance

Sustainable production of sorghum, Sorghum bicolor (L.) Moench, depends on effective control of insect pests as they continue to compete with humans for the sorghum crop. Insect pests are a major constraint in sorghum production, and nearly 150 insect species are serious pests of this crop worldwide and cause more than 9% loss annually. Annual losses due to insect pests in sorghum have been estimated to be

Biochemical interactions for antibiosis mechanism of resistance to Chilo partellus (Swinhoe) in different maize types

1,089 million in the semiarid tropics (ICRISAT Annual report 1991. International Crop Research Institute for Semi-arid Tropics. Patancheru, Andhra Pradesh, India, 1992), but differing in magnitude on a regional basis. Key insect pests in the USA include the greenbug, Schizaphis graminum (Rondani); sorghum midge, Stenodiplosis sorghicola (Coquillett); and various caterpillars in the Southern areas. For example, damage by greenbug to sorghum is estimated to cost US producers

Temperature-dependent development of diapausing larvae of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

248 million annually. The major insect pests of sorghum on a global basis are the greenbug, sorghum midge, sorghum shoot fly (Atherigona soccata Rond.), stem borers (Chilo partellus Swin. and Busseola fusca Fuller), and armyworms (Mythimna separata Walk and Spodoptera frugiperda J.E. Smith). Recent advances in sorghum genetics, genomics, and breeding have led to development of some cutting-edge molecular technologies that are complementary to genetic improvement of this crop for insect pest management. Genome sequencing and genome mapping have accelerated the pace of gene discovery in sorghum. Other genomic technologies, such as QTL (quantitative trait loci) mapping, gene expression profiling, functional genomics, and gene transfer are powerful tools for efficient identification of novel insect-resistance genes, and characterization of the key pathways that regulate the interactions between crop plants and insect pests leading to successful expression of the host plant defense. Traditional breeding methods, such as germplasm evaluation and enhancement, backcrossing, pedigree selection, and recurrent selection continue to play important roles in developing insect-resistant cultivars with major resistance genes; and new cultivars with enhanced resistance to several important insect pests are released continuously. Future research efforts should focus on identification of new sources of resistance, characterization of resistance genes, and dissecting the network of resistance gene regulation. Collaboration between research institutions and the sorghum industry as well as international cooperation in utilization of emerging knowledge and technologies will enhance the global efforts in insect pest management in sorghum.

Consequences of diapause on post-diapause development, reproductive physiology and population growth of Chilo partellus (Swinhoe): Diapause physiology of Chilo partellus

Variation in performance and abundance of herbivorous insects is attributed to variation in host plant quality, being determined by nutritional composition, allelochemistry and specific anatomical features. Present studies were undertaken to gain an understanding on the role of different biochemical factors in plant defense to Chilo partellus in diverse maize types with variable morphological and favorable agronomic traits. All the white and yellow kernel maize genotypes tested had significantly lower deadhearts and more adverse effects on one or the other biological parameters of C. partellus, as compared to the resistant check, CML 334. The phenolic acids viz., ferulic acid and p-coumaric acid, and the nutritional biochemical factors such as protein, oil, chlorophyll-b, total chlorophyll and total carotenoid showed significant negative correlations, while total sugars and starch had positive correlation with pupal period of C. partellus. Oil content showed significant positive correlation with larval weight, and chlorophyll-a negative correlation with larval and pupal weights of C. partellus. Iron and zinc contents in maize seedlings showed significant positive correlation with pupal weight, whereas zinc content showed negative correlation with plant deadhearts, larval survival and adult emergence of C. partellus. Present studies show that different maize types expressed antibiosis mechanism of resistance to spotted stem borer, while the amount of phenolic acids and the nutritional biochemical constituents were highly variable in their seedlings, suggesting that the maize plant defense against C. partellus could be due to concentration of particular biochemical constituent and/or interaction with different biochemical compounds.

A common HPLC-PDA method for amino acid analysis in insects and plants

Temperature-dependent development rate, percent diapause induction (hibernation at low temperature and aestivation at high temperature), and survival of diapausing larvae of Chilo partellus (Swinhoe, 1885) were examined on 13 constant temperatures ranging from 8 to 40°C. Development of hibernating and aestivating larvae occurred from 10 to 25°C and 27-38°C, respectively. However, no development occurred at 8°C and 40°C. To determine actual thermal conditions that affect development and trigger both kind of diapause (hibernation and aestivation), various thermal parameters were estimated by fitting the development rate data to two linear (Ordinary equation and Ikemoto & Takai) models and thirteen non-linear models. The lower thermal thresholds (Tmin) for development of diapausing larvae of C. partellus were calculated as 9.60°C and 10.29°C using the ordinary linear model and Ikemoto & Takai model, respectively. Similarly, the thermal constants (K) estimated using the ordinary linear model was 333.33 degree-days and that estimated with Ikemoto & Takai model was 338.92 degree-days. Among the non-linear models, Lactin-2 followed by Lactin-1 were found to be the best as these models estimated the critical temperatures (Tmin, Tmax and Topt) similar to those of observed values. Conclusively, the Ikemoto & Takai linear model and Lactin-2 followed by Lactin-1 non-linear models are useful and efficient for describing temperature-dependent development and estimating the temperature thresholds of diapausing larvae of C. partellus. Our findings provided fundamental information for estimation of thermal requirement and temperature based development models for diapausing larvae of C. partellus. This information will be highly useful for predicting the occurrence, seasonal emergence, number of generations and population dynamics of C. partellus.

Morphological changes in Chilo partellus (Swinhoe) undergoing diapause

We investigate the effects of diapause on post‐diapause development, reproductive physiology and population growth of Chilo partellus (Swinhoe) (Crambidae: Lepidoptera). Aestivating and hibernating larvae of C. partellus are exposed to diapause terminating conditions (consisting of an LD 12 : 12 h photocycle at 27 ± 1 °C and 65 ± 5% relative humidity with a fresh diet) to terminate the diapause and observations are made on percentage pupation, pupal duration and weight, adult reproductive performance and population growth parameters. We find that the diapause in C. partellus significantly reduces the percentage pupation and weights of pupae, ultimately lowering the weight and reproductive performance of adults. Reduced weights of adult females are found to be directly associated with a lower number of egg cells in ovaries. Nevertheless, the reproductive performance of C. partellus males is also found to be greatly affected in the diapause (hibernation and aestivation) experiencing population in terms of the deposition of a lower number of spermatophores and eupyrene sperm in the reproductive tracts of females compared with the nondiapausing population. The results of the present study clearly indicate that a reduction in longevity, fecundity and egg viability, as well as a reduced rate of deposition of spermatophores and eupyrene sperm, in a diapause experiencing population of C. partellus ultimately leads to a reduction in population growth parameters, thus having implications for bio‐ecology and population dynamics under a changing climatic scenario.