Relating rainfall and vegetation greenness to the biology of spur-throated and Australian plague locusts
Abstract:• Rainfall and vegetation greenness are widely claimed to influence fat content and egg development in locusts. Body size, abdominal fat and egg length of spur-throated Austracris guttulosa and Australian plague Chortoicetes terminifera locusts were related to the normalized difference vegetation index (NDVI; a greenness indicator) to test these assumptions and quantify biological responses.
• Cumulative rainfall was highly correlated with NDVI values of an area (25 × 25 km) surrounding the trap to which locusts were attracted. Catches of locusts were greater in hotter periods preceding rain, associated with an increase in NDVI indicative of brown (0.298) versus green (0.465) vegetation.
• Pre-overwintering descendent A. guttulosa were larger and fattier than post-overwintering antecedents. Egg maturation of antecedents occurred coincident with increasing NDVI. Higher abdominal fat in pre-overwintering locusts was positively associated with higher NDVI.
• Male C. terminifera of two descendent generations were larger than their antecedents but only pre-overwintering locusts were significantly fattier than their predecessors. Only pre-overwintering females were significantly larger than their predecessors and no generation was significantly fattier than any other. Fat content was negatively correlated with egg maturation and differed significantly with NDVI, although strong and consistent relationships were not obtained.
• The findings suggest that locust–environment interactions are species- and habitat-specific. If A. guttulosa hoppers develop during periods when regional NDVI exceeds 0.4, fatter adults will arise. The elucidation of relationships between greenness, fat and egg development in C. terminifera is unlikely using NDVI values from areas comprising mixtures of monocotyledonous and dicotyledonous vegetation.