Abu Bakar Muhammad Raza

Post-exposure temperature influence on the toxicity of conventional and new chemistry insecticides to green lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae).

Chrysoperla carnea (Stephens) is an important biological control agent currently being used in many integrated pest management (IPM) programs to control insect pests. The effect of post-treatment temperature on insecticide toxicity of a spinosyn (spinosad), pyrethroid (lambda cyhalothrin), organophosphate (chlorpyrifos) and new chemistry (acetamiprid) to C. carnea larvae was investigated under laboratory conditions. Temperature coefficients of each insecticide tested were evaluated. From 20 to 40 °C, toxicity of lambda cyhalothrin and spinosad decreased by 2.15- and 1.87-fold while toxicity of acetamiprid and chlorpyrifos increased by 2.00 and 1.79-fold, respectively. The study demonstrates that pesticide effectiveness may vary according to environmental conditions. In cropping systems where multiple insecticide products are used, attention should be given to temperature variation as a key factor in making pest management strategies safer for biological control agents. Insecticides with a negative temperature coefficient may play a constructive role to conserve C. carnea populations.

Resistance of green lacewing, Chrysoperla carnea Stephens to nitenpyram: Cross-resistance patterns, mechanism, stability, and realized heritability

The green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) is a major generalist predator employed in integrated pest management (IPM) plans for pest control on many crops. Nitenpyram, a neonicotinoid insecticide has widely been used against the sucking pests of cotton in Pakistan. Therefore, a field green lacewing strain was exposed to nitenpyram for five generations to investigate resistance evolution, cross-resistance pattern, stability, realized heritability, and mechanisms of resistance. Before starting the selection with nitenpyram, a field collected strain showed 22.08-, 23.09-, 484.69- and 602.90-fold resistance to nitenpyram, buprofezin, spinosad and acetamiprid, respectively compared with the Susceptible strain. After continuous selection for five generations (G1-G5) with nitenpyram in the laboratory, the Field strain (Niten-SEL) developed a resistance ratio of 423.95 at G6. The Niten-SEL strain at G6 showed no cross-resistance to buprofezin and acetamiprid and negative cross-resistance to spinosad compared with the Field strain (G1). For resistance stability, the Niten-SEL strain was left unexposed to any insecticide for four generations (G6-G9) and bioassay results at G10 showed that resistance to nitenpyram, buprofezin and spinosad was stable, while resistance to acetamiprid was unstable. The realized heritability values were 0.97, 0.16, 0.03, and -0.16 to nitenpyram, buprofezin, acetamiprid and spinosad, respectively, after five generations of selection. Moreover, the enzyme inhibitors (PBO or DEF) significantly decreased the nitenpyram resistance in the resistant strain, suggesting that resistance was due to microsomal oxidases and esterases. These results are very helpful for integration of green lacewings in IPM programs.

Population dynamics of citrus leaf miner on different varieties of citrus in correlation with abiotic environmental factors in Sargodha District, Punjab, Pakistan

From January 2010 to December 2011, samples of leaves from citrus varieties Kinnow, Musambi and Feutral were taken from the five tehsils (administrative subdivisions) of Sargodha District in Pakistan including Sargodha, Bahalwal, Silanwalli, Sahiwal and Kotmomin, to study the population trends in citrus leaf miner (CLM), Phyllocnistis citrella (Stainton) (Lepidoptera: Gracillariidae), and its correlation with various environmental factors: (temperature, humidity and rainfall); plant morphological factors: moisture contents of leaves, leaf thickness, surface area (cm2), and biochemical percentage of calcium, potassium and magnesium in leaves. The maximum population of CLM was observed on Kinnow and Feutral, followed by Musambi. The effect of these factors on the larval population was 8.39- 2.30(Mg)+2.73(K)-0.398(Ca)-0.100(Temp)0.038(Humidity)+0.567(Rain)+0.07(Moist) 1.01 (Thickness)-0.022(Surface area). This equation revealed that magnesium, calcium, temperature, humidity, leaf thickness and leaf surface area are negatively correlated with larvae population, whereas potassium, rainfall and moisture are positively correlated with larvae population.

Effects of different host species on the life history of Bracon hebetor

Bracon hebetor (Hymenoptera: Braconidae) is a generalist idiobiont ecto-parasitoid that parasitizes a wide range of Lepidoptera and even some phylogenically distant weevil species (Coleoptera; Curculionidae). In the present context, our aim is to find the most suitable host for efficient laboratory rearing of B. hebetor. We compared fitness traits of this parasitoid wasp on five host species, four species belonging to the Lepidoptera, viz. Galleria mellonella (Pyralidae), Helicoverpa armigera and Spodoptera litura (Noctuidae), Sitotroga cerealella (Gelechiidae), and one to the Coleoptera, the alfalfa weevil Hypera postica (Curculionidae). We determined the parasitic potential, paralysis, daily oviposition rate, development time, total adult progeny, sex ratio and survival. Fecundity was followed during five consecutive days and oviposition period was determined, all under laboratory conditions. The best results were obtained on the wax moth larvae (G. mellonella) for which B. hebetor proved the highest biological activity in term of paralysis, parasitism and oviposition as compared to other tested host species. In Galleria mellonella, total eggs laid per female per five days and egg-adult survivorship were higher and sex ratio was highly biased toward females, as compared to Hypera postica. Intermediate biological activities were found on Helicoverpa armigera, Spodoptera litura and Sitotroga cerealella. These contrasting results show that the plasticity of this species could also represent an important fitness cost difference in performance, which is discussed in terms of phylogenetic distance of the host species (particularly Pyralidae). In conclusion, the possible application of these results can be used in the economically important field of biological control and improve storage of products affected by insect pests.

Presence of less-preferred hosts of the aphid parasitoids Aphidius ervi and Praon volucre reduces parasitism efficiency

Parasitoids are characterized by a defined range of hosts, either more specialist or generalist. Under natural conditions, females may encounter different host species on the same plant or in the same location. In this case, their preference for one host could influence their choice. However, the presence of less suitable hosts may also affect their choice and, in some cases, may reduce their interest in a patch where both preferred and less preferred hosts are available. The aim of the present study was to test the consequences of the simultaneous presence of three cereal aphids (Sitobion avenae Fabricius, Metopolophium dirhodum Walker, and Rhopalosiphum padi Linnaeus) on the parasitism by two of their parasitoids, Aphidius ervi Haliday and Praon volucre Haliday. Firstly, in the no-choice experiment, A. ervi parasitized on S. avenae at a significantly higher rate as compared to M. dirhodum, whereas no parasitism on R. padi was observed. P. volucre parasitized the three species of cereal aphids with a significant preference for S. avenae. Interestingly, when two or three host species were offered simultaneously in the same quantity to pairs of parasitoids, the level of parasitism was less than that observed for one host species alone. This observation exhibits a distractive effect on non-host species, from the defense mechanism of a non-suitable host or from the perception of bad quality patches. These results raise the question of the practical application of inundative release of parasitoids for biocontrol when several hosts are available simultaneously.