Larval Relative Growth Rate Research Articles

Mandibular Adduction Force of Heliothis virescens (Lepidoptera: Noctuidae) Larvae Fed the Insecticidal Crystals of Bacillus thuringiensis

A gauge was developed to measure the mandibular adduction force of Heliothis virescens (F.) intoxicated with Bacillus thuringiensis . The gauge was calibrated by loading weights on the assembly similar to the way the mandibles move. The larvae were fed for 24 h on a diet containing a lethal dose of 20 μg/g of the insecticidal crystals (parasporal crystals) of B. thuringiensis subsp. kurstaki , strain HD-73. The diet in the control did not contain the crystals. Cessation of feeding as a result of the microbial intoxication was characterized by measuring the larval relative growth rate and the relative consumption rate. A negative regression equation of the nutritional indices was obtained for larvae treated with B. thuringiensis ; the equation expressed feeding arrest and weight loss. Control larvae consumed the diet and gained weight normally. The mandibular adduction force in both treated and control larvae was similar, indicating that mandibular function was not impaired by microbial intoxication.

Factors Facilitating the Continued Presence of Colotis evagore (Klug, 1829) in Southern Spain

Colotis evagore (Klug) is a multivoltine pierid butterfly that has repeatedly invaded the Iberian Peninsula from Africa over the last four decades. In 1983 it invaded Spain, reproducing successfully there on its foodplant, Capparis spinosa L. During the cold season this plant is not available in most areas of Spain, and the butterfly must find alternative foodplants to maintain its populations in this newly colonized territory. Our data show that C. evagore is unable to survive on alternative cruciferous hosts, and incapable of entering diapause to avoid inhospitable times of the year and the absence of host plants. The relative growth rate of larvae depends on temperature; the threshold temperature for development is 12?C, and the estimated physiological time for larval development is 162.5?d. Our observations show that C. evagore has survived continually in certain coastal sites in southern Spain since 1983. Microenvironmental conditions in these sites are particularly favourable for the foodplant. Hence, the plant is available throughout the year, allowing the caterpillars to complete successfully their life-cycle.

Compound interactions effects of plant antioxidants in combination with carbaryl on performance ofTrichoplusia ni (Cabbage Looper)

Plant chemicals naturally exist in complex mixtures, which can interact either additively, synergistically, or antagonistically. We investigated the potential interactions of three naturally occurring antioxidants- nordihydroguaiaretic acid (NDGA), safrole, and α-tocopherol-with the general insecticide carbarayl to affect the performance of cabbage looper larvae (Trichoplusia ni). The cabbage looper is known to produce a mixed-function oxidase enzyme system in response to the presence of carbaryl. We proposed that plant antioxidants would interfere with enzymatic oxidation, enhancing the susceptibility of this insect to carbaryl. Insects were fed artificial diets containing each antioxidant alone or in pairwise combinations with the insecticide carbaryl to test for their effects on the insect's nutritional measurement indices. The three antioxidants tested were not equally effective individually against insect survivorship and interacted differentially in combination with the insecticide. The nutritional indices were measured on insects fed diets containing the chemicals at nonlethal doses. Insects fed 0.001 % wet wt NDGA diets grew 1.62 times less, and had gross and net conversion efficiencies reduced 3.20 and 3.63 times, respectively, compared to the control larvae. Carbaryl (0.002% wet wt) in combination with NDGA acts as an antagonist to the effects mentioned above, while safrole (1 × 10(-4) wet wt) had an additive effect when combined with the insecticide, reducing 1.76 times larval relative growth rate and efficiency of conversion of ingested food in respect to the control. The larvae fed significantly more (1.2 times) on both insecticide and safrole diets than on the controls or their combined diets. Larvae fed α-tocopherol alone or in combination with carbaryl had similar growth and conversion efficiencies as controls. We conclude that the effects of different combinations of compounds cannot be predicted a priori and must be determined experimentally.

Crude extracts of asteraceous weeds

Petrol and ethanolic extracts of six asteraceous weeds were added to artificial diets to screen for growth inhibition and mortality of the variegated cutworm,Peridroma saucia (Hbn). Petrol and ethanolic extracts ofArtemisia tridentata andChamomilla suaveolens and ethanolic extracts ofChrysothamnus nauseosus andCentaurea diffusa severely inhibited larval growth at five times the natural concentrations. The twoC. suaveolens extracts and the ethanol extract ofA. tridentata were active at the natural concentration (100%) and were further examined at 20, 40, 60, and 80% of this level. Inhibition of larval growth was directly related to concentration for each of the three extracts tested. EC50s (effective concentration to inhibit growth by 50% relative to controls) for the three extracts were 36-42% of the naturally occurring level in the plants. Nutritional indices were calculated for secondinstarP. saucia feeding on the activeA. tridentata EtOH extract and the petrol extract fromC. suaveolens. Addition of the activeA. tridentata EtOH or theC. suaveolens petrol extract to the diet resulted in significant reduction in the relative growth rate of larvae, although theA. tridentata extract was much more inhibitory. Dietary utilization was significantly lower for larvae fed theA. tridentata EtOH extract.

Effects of PIX, a Plant Growth Regulator, on Allelochemical Content of Cotton and Growth of Tobacco Budworm Larvae (Lepidoptera: Noctuidae)

In 1982, second-instar tobacco budworms, Heliothis virescens (F.), were fed leaves, bracts, and squares without bracts (buds) of ‘Stoneville 213’ cotton, Gossypium hirsutum L., treated with PIX (1,1-dimethyl-piperidinium chloride). PIX was applied at rates 0.0, 0.4, 1.3, and 3.9 liters/ha. Two applications of PIX were made 2 weeks apart. Plant tissues were analyzed for allelochemicals. Relative growth rate (RGR), relative consumption rate (RCR), and efficiency of conversion of ingested food to body tissue (ECI) were measured. Gossypol in buds and leaves was increased by the application of PIX; however, anthocyanin in buds and tannin and total flavonoids in leaves were decreased. Treatment with PIX did not decrease the nutritional indices of larvae. Other than an increase in larval RGR on leaves, PIX had no major effects on nutritional indices. The increase in RGR on leaves possibly was due to decreases in tannin and total flavonoids and possible increases in percentage nitrogen. RGR was greatest on buds while ECI was greatest on leaves. In a test of ’Stoneville 213’ bud parts, anthers were more nutritious than petals or calyx.

Lacustrine Seston and Other Factors Influencing the Blackflies (Diptera: Simuliidae) Inhabiting Lake Outlets in Swedish Lapland

The blackfly (Diptera: Simuliidae) assemblages of three localities in a river system in Swedish Lapland were examined. One locality was at a lake outlet, one further down in the same river and one in a nearby small forest stream. The three dominant species at the outlet were virtually absent from the other localities, where, conversely, most larvae belonged to species not present at the outlet. Total larval abundance was very much higher at the outlet, where larvae were present for a shorter period than elsewhere. Even within a few hundred metres from the outlet the relative growth rate of larvae was slower than at the outlet, and only a little further downstream the species prevailing at the outlet were replaced by other species. Large particles, such as phytoplankton and coarse detritus, occurred in similar numbers everywhere, and at all times, and therefore did not seem to control the abundance of blackfly larvae. After examining the role of temperature and substrate it is concluded that food, that is small particles possibly down to colloidal size, provide the resource maintaining the huge larval aggregations immediately below the lake outlet. These particles, produced on the lake bottom by decomposition processes during the winter, are washed out into the river at ice-melt. Changes in their availability and/or nutritive value limit their usefulness as food to the section of the river immediately downstream from the lake. Additional benefits may accrue to larvae growing up in these areas of extreme population density.