Striped Cucumber Beetle (Acalymma vittatum)

The striped cucumber beetle is a specialist on cucurbits. Adults feed on foliage, stems, flowers and fruit, while larvae feed on roots and sometimes on the rind of the fruit that contacts the ground. Adults are also a key vector of economically important cucurbit diseases, most notably bacterial wilt. As a result, this abundant, widespread, and persistent pest can be difficult to manage effectively and poses a challenge for growers year after year.

Life cycle of striped cucumber beetle

Adult striped cucumber beetles emerge from the leaf litter in the spring once average daily temperatures reach 55°F – typically several weeks before cucurbits are planted. They feed on a wide range of non-preferred host plants (including hawthorn, willow, goldenrod, and apple) as they wait for the first cucurbits to become available. 

Once cucurbit foliage is present, adult beetles aggregate there to feed and mate. Adults colonize the crop over an extended period in the early summer. Feeding damage by beetles at this time can severely harm young plants. 

Adults typically live for 2 months and females lay eggs continuously throughout their lives. An average female in good condition will lay around 125 eggs, though occasionally, an individual can lay as many as 1,000 eggs. 

Development of eggs and larvae is highly dependent on temperature and varies across regions and years. In New York State, adults begin to lay eggs in the soil at the base of cucurbit plants about 2 weeks after mating. Eggs develop within a week before hatching into larvae. Larvae feed on roots and develop through three instars over 3 to 4 weeks, then pupate underground. The pupal stage lasts for around a week, after which adult beetles emerge from the soil, typically around late July.

These new adults feed on mature cucurbits and produce a second generation of eggs, larvae, and pupae, which emerge as second generation adults in early September – this two-generation life cycle is common across New York State. Upon emergence, second generation adults feed briefly to build up reserves before digging an inch or two into nearby leaf litter to overwinter. 

Management of striped cucumber beetle

A targeted IPM strategy for striped cucumber beetles can provide an opportunity for growers to cut costs. Routine scouting was determined to be more cost effective than preventative foliar insecticide treatments in fields across the midwest. Scouting thresholds for pumpkin, squash, and melon are 1 beetle per seedling, and up to 5 beetles per plant after the 4-leaf stage. Thresholds for cucumber and muskmelons are lower because these cultivars are susceptible to bacterial wilt: 1 beetle per every 2 seedlings, or 1 beetle per plant past the 4-leaf stage. Weekly scouting of foliage is recommended.

Physical control

• Floating row covers or exclusion netting – If plantings are small enough, this can be a highly effective way of reducing beetle damage early in the season, though the covers must be removed after flowers emerge to facilitate pollination.
• Black plastic mulch – Covering the soil around the base of cucurbit plants can reduce the survival of cucumber beetle larvae when compared to exposed soil, but only if temperatures exceed a critical threshold.
• Attract-and-kill traps – Commercially available traps for cucumber beetles are baited with synthetic cucurbit flower volatiles. However, these traps can also attract and kill important pollinators. Current work is trialing attract-and-kill traps baited instead with the aggregation pheromone produced by male striped cucumber beetles, which broadly attracts cucurbit pests.

Cultural control

• Perimeter trap cropping – The principle of trap cropping is to provide a more attractive host for cucumber beetles than the cash crop. This attractive host is planted along field edges and used to draw the beetles away from the cash crop, where it can be managed with targeted insecticides. Blue hubbard squash and buttercup squash are particularly attractive to cucumber beetles, and planting these varieties on field edges two weeks before the cash crop can be an effective trap.
• Companion planting – This has not been studied extensively to manage cucumber beetles, but has shown some early promise. In preliminary trials, planting alternating rows of melon and radish, with a perimeter of buckwheat reduced beetles and increased melon yield. Alternating rows of amaranth or sunn hemp have also been shown to reduce beetle densities and damage in cucumber and zucchini. 

Biological control

• Cucumber beetle parasitoids – A tachinid fly (Celatoria setosa) and brachonid wasp (Centistes diabroticae) parasitize striped cucumber beetles. Both parasitoids occur naturally in New York, and rates of parasitism are high in some beetle populations (up to 43% with C. setosa and up to 54% with C. diabroticae). However, the extent to which these parasitoids reduce beetle populations, feeding damage, and the spread of wilt is unknown.
• Insect-infecting nematodes (Steinernema riobravis) – Introducing these commercially available nematodes to the soil via drip irrigation in early summer (to target cucumber beetle larvae) or early fall (to target overwintering cucumber beetle adults) can reduce adult emergence.
• Generalist predators – Wolf spiders, harvestmen, ground beetles, and lady beetles all eat striped cucumber beetles. The presence of wolf spiders, specifically, was demonstrated to reduce beetle feeding and increase the yield of cucumber and squash in small plots. 

Chemical control

• Systemic insecticides that contain either thiamethoxam or cyantraniliprole are effective at reducing beetle damage on cucurbit seedlings. Typically, a soil application or transplant tray drench treatment of thiamethoxam is sufficient to protect the crop until near flowering. In contrast, a soil application or transplant tray drench of cyantraniliprole likely will need to be followed with a foliar insecticide application 2-3 weeks after planting.
• There are many foliar insecticide options for cucumber beetle control. However, many of these insecticides are harmful to pollinators. To minimize harm to pollinators, applications should be made before flowering. If applications are needed during flowering, it is recommended to make applications at night when bees are not foraging.

There are three chemicals approved for organic use:

• Kaolin clay – Clay must be applied before beetles arrive, as it acts as a physical colonization deterrent and irritates and disorients beetles searching for host plants. Repeated applications will be needed, especially after rain because the material will wash off the leaves.
• Select pyrethrins – Pyrethrins occur naturally in chrysanthemum flowers, and are now manufactured for commercial use. They act on the insect nervous system once they have been ingested, causing paralysis and death.
• Spinosyns – Spinosyn compounds are naturally produced by some types of bacterial fermentation, and have been isolated and commercially synthesized. They act as an acute poison, causing paralysis and death to insects after ingestion. 

For detailed information about insecticide options, rates, pre-harvest intervals and bee precautions, refer to the Cornell Vegetable Guidelines. 

Any time you use a pesticide, you must read and follow the label directions and comply with all applicable laws and regulations related to pesticide use. Also be sure that any pesticide used is approved for use in your country and state/province.