The mortality of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) neonate larvae in relation to drop‐off and soil surface temperature: the dangers of bungy jumping

Abstract

The first larval instar has been identified as a critical stage for population mortality in Lepidoptera, yet due to the body size of these larvae, the factors that contribute to mortality under field conditions are still not clear. Dispersal behaviour has been suggested as a significant, but ignored factor contributing to mortality in first-instar lepidopteran larvae. The impact that leaving the host plant has on the mortality rate of Helicoverpa armigera neonates was examined in field crops and laboratory trials. In this study the following are examined: (1) the effects of soil surface temperature, and the level of shade within the crop, on the mortality of neonates on the soil after dropping off from the host plant; (2) the percentage of neonates that dropped off from a host plant and landed on the soil; and (3) the effects of exposure to different soil surface temperatures on the development and mortality of neonates. The findings of this study showed that: (1) on the soil, surface temperatures above 43°C were lethal for neonates, and exposure to these temperatures contributed greatly to the overall mortality rate observed; however, the fate of neonates on the soil varied significantly depending on canopy closure within the crop;(2) at least 15% of neonates dropped off from the host plant and landed on the soil, meaning that the proportion of neonates exposed to these condition is not trivial; and (3) 30 min exposure to soil surface temperatures approaching the lethal level (>43°C) has no significant negative effects on the development and mortality of larvae through to the second instar. Overall leaving the plant through drop-off contributes to first-instar mortality in crops with open canopies; however, survival of neonates that have lost contact with a host plant is possible, and becomes more likely later in the crop growing season.

Stay or move: how Bt‐susceptibleHelicoverpa armigeraneonates behave on Bt cotton plants

“…The Bt‐susceptible larvae moving off plant parts with high Bt content may encounter less toxic plant parts. Helicoverpa armigera larvae are likely to re‐establish on a plant if they drop to the ground within 5 cm of the stem (Perović et al, ). They have been able to survive off the plant for at least 1 h, and travel up to 80 cm from where they dropped to the ground (for a similar finding see Terry et al, ).…”

Is the effect of priming plants, and a functional JAR1, negligible on the foraging behaviour and development of a generalist lepidopteran, Helicoverpa armigera?

“…Helicoverpa armigera larvae were found to drop off more often from WT plants induced with mites than from plants induced by caterpillar feeding or from non-induced plants. We have shown that H. armigera larvae do not survive long on the ground (Perovic et al, 2008). However, in contrast, a higher percentage of neonate fall armyworms Spodoptera frugiperda (JE Smith) remained on herbivore-induced cowpea seedlings [Vigna unguiculata (L.) Walpers] (Carroll et al, 2008).…”

“…Transfer was done by catching their silk using a fine camel-hair brush and allowing them to drop onto the plant surface, thus mimicking natural drop-off behaviour (Perovic et al, 2008), avoiding damaging the larvae and disturbing their behaviour. All larvae used in these studies were newly hatched.…”

Rf and Microwave Low Power Dielectric Heating Using Parallel Plate Applicator to Control Insect Pests on Tomato Plant

“…• C the eggs were laid on a leaf [18][19][20][21][22][23]. 90% of eggs were hatched at 200 W and 76% eggs hatched at 250 W after the exposure.…”